The following began as my working notes when designing a windsurfer I recentlybuilt Irsquod do a bit of the design leave it come back to it and forget what Irsquod done andwhich design I was going with Therefore these notes were written primary to remindme of what I did Once I started building it I decided to continue the documentationjust in case I was every crazy enough to do it again
The design was from scratch and this was my first attempt at building a windsurferIrsquod done small repairs before and built a canoe using a mould so had some prior fibre-glassing experience but had not done any vacuum bagging
The notes are not a step-by-step how-to More importantly they are based on a firsttime backyard board builders experience Irsquom sure there are many things I did whichcould be improved or done entirely differently There is not that much info on design-ing and building a windsurfer However info on building surfboards canoes sailingboats is more plentifully and can be useful The best reference that gives detailed stepby step information for windsurfers was at the website httpwwwecboardscouk Itis titled Building a composite windsurfer and gave details on building a speed board Ifound any info provided on the web to be invaluable hence I decided to put these notesout there for anyone else attempting a similar project
Before embarking on building a board you have to ask the question why If it isto save money donrsquot do it The material costs equated to roughly half the retail priceof on equivalent board However if you factor in labour therersquos certainly no savingsRealistically it was equivalent to a month full time I took 6 days off work and spent thebest part of a month worth of weekends on it It took far longer than I had anticipatedThis is partly because it was my first time and I was learning as I went Irsquod make smallmistakes which then took time to fix
For me the motivation behind the project started with an old raceboard that wasleaking Irsquod previously fixed the centre board box and suspected it was leaking SoI took the drastic step of cutting a 1times 01 m slot down the middle of the board andrebuilt the centre box It turned out there was no water there however there was watergetting in the front The board was already 18 kg and with more major repairs wouldbe getting close to 20 kg also it was 20 years old Time for a new or better 2nd-handboard Only problem is new boards of this kind are hard to get Exocet and Starboardhave started making them and Mistral appears to resurrecting the equipe On the 2nd-hand market a couple of boards appear every 12 months Australia wide So with thecentre board box built and some vacuum bagging skills acquired I decided to go all theway and build from scratch I also liked the idea of designing and building myself
Would I do it again Probably not Overall I was happy with the result Whileitrsquos obviously an amateur build it came out under weight and without any flaws thatwould effect performance Basically this is my light wind ldquosailingrdquo board maybe Irsquollgive racing a go but it wasnrsquot build with that in mind Irsquod tried wide-style early planersbut found them a bit one-dimensional My biggest sail is 85m2 which on a 85cm wideboard gives me planing threshold of sim 8 knots minimum (ie realistically a ldquosteadyrdquowind averaging 10knots) But if itrsquos a summerrsquos day with an average 8 knots Irsquod betempted to venture out and end up struggling in the lulls So I experimented with anold raceboard and found I was having heaps more fun in the 8-12knots winds
Contents
1 Board design 511 Maximum dimensions 512 Rocker profile 513 Deck centre-line profile 614 Vee concaves tail kick 615 Planshape 616 Deck cross section and rails 617 Data files 718 Design weight 1219 Material costs 13110 Time required to build 14
2 Centreboard 1521 Design of centreboard 15
211 Aerofoil section 15212 Planshape 16
22 Construction of centreboard 1623 Centreboard Box 17
3 Mast track fin-box and footstrap plugs 2031 Mast track 2032 Finbox and Footstrap plugs 20
4 Board Construction 2241 Shaping 22
411 Templates 22412 Core 23413 Rocker and deck 23414 Vee 23415 Planshape 23416 Rails 23
42 Laminating 24421 CarbonHDF to bottom 28422 CarbonHDF to deck 29423 Fitting the fittings 29
5 The finished product 3551 Photos from Inverloch 25042010 39
A Tooling 44A1 Compressor 44A2 Vacuum controller 44A3 Hotwire cutter 46A4 Hotwire voltage control 46
B References and links 49
4
Chapter 1Board design
11 Maximum dimensions
maximum length = l = 3800 mmmaximum width = wm = 640 mmmaximum thickness = tm = 180 mm
12 Rocker profile
The bottom rocker profile ρ (in mm) is defined by the equation
ρ(x) =
0 x lt 800
(xminus 800)4
3times 1011 x gt 800(11)
where x (in mm) is the lengthwise coordinate and ρ is measured relative to the hori-zontal datum z = 0 where z is the vertical coordinate as defined in figure 11 Henceat the stern of the board (ie for x lt 800 mm) the rocker is a true flat Forward ofx = 800 mm the rocker is defined by a quartic giving a maximum rocker value at thebow of the board of ρ = 270 mm The quartic curve generates very little rocker initiallyitrsquos only around x = 2000 m that the rocker starts to kick in
Actually the rocker profile given by (11) can be expressed in terms of two inde-pendent parameters the maximum rocker ρm and the coordinate where the rockerbegins x f Rewriting (11) in terms of these two parameters gives
ρ(x) =
0 x lt x f
ρm
(xminus x f
l minus x f
)4
x gt x f(12)
where l is the maximum length
5
Design and construction of a windsurfer longboard
13 Deck centre-line profile
The deck profile was generated by sketching a spline keeping in mind I didnrsquot wantthe trailing edge of the centreboard to protrude through the deck when it was in theretracted position The centreboard has a maximum chord of 170 mm so the maximumthickness of the board was set to 180 mm
14 Vee concaves tail kick
The reference board I used during the design was heavily concaved figure 12 Irsquom notsure how one would accurately shape these contours In any case most modern boardsseem to have abandoned concaves A simple vee should do the job of counteracting theslapping tendency of a flat hull which concaves also serve to do Concaves may assistis lateral resistance but probably add drag there seems to be very little information ontheir effect In the end I decided to go for a small amount of vee only no tail kick orconcaves The actual vee is constant at 1 degree along the full length
15 Planshape
Figure 13 shows the planshape of the bottom of the board The rails are parallel forapproximately the range x = 1700 to x = 2100 mm where the width is the maximumvalue wm = 640 mm The planshape was generated by a spline sketch and hencecannot be represented in equation form although its not far off an ellipse
16 Deck cross section and rails
Finally the deck and rail profiles are required to completely specify the geometry ofthe board Raceboards have sharp rails which run almost the complete length of theboard This feature greatly simplifies the design since one cross sectional profile canbe specified and simply scaled appropriately based on the thickness and width of theboard at a given x coordinate I played around with using quadratics arcs and thelike to define the cross section but in the end it was simpler just to sketch a spline thatlooked about right Figure 14 shows the normalised cross section used for all locationsIrsquoll probably knock the corner off this profile near the nose of the board where sharprails are more of a liability
Individual cross sectional profiles for the back half of the board are shown in fig-ure 15 and for the front half of the board in figure 16 The area bounded by theindividual cross sections can be calculated by numerically integrating the curves andhence the volume of the board is calculated from the summation
V = A1∆x1 + A2∆x2 + A3∆x3 + + An∆xn =n
sumi
Ai∆xi
where Ai is the area of the ith cross section and ∆xi is the ldquothicknessrdquo of the crosssection slice For the data given above the volume turns out to be
V = 252 litres
6
Design and construction of a windsurfer longboard
The surface area of the board can be found by calculating the length of individuallines show in figures 15 and 16 For the deck and rails this length is given by integrat-ing the upper curves using the formula
S =int w2
minusw2
radic1 +
(dzdy
)2
dy
If this is done for many x locations on the board then the surface area is given by thesummation
A =n
sumi
Si∆xi = 256 m2 deck and rails
A similar calculation can by done for the bottom of the board but it is much simplersince the lines are straight and at a given x location
S =w
cos θ
where θ is the vee angle which is small and hence S asymp w so
A =int 3800
0w dx = 195 m2 bottom
where w is the width of the board which is a function of x
17 Data files
Plain text files containing the coordinates for the
Figure 12 The board used as a rough guide for the design The actual board I designedis quite different the only dimension I matched was the maximum rocker (nose kick)Itrsquos good to have something to reference your design against just to ensure you donrsquotdesign something ldquooff the scalerdquo
9
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
x (mm)
0
y (mm)
l = 3800mm
w
Stern
500 1000 1500 2000 2500 3000 3500-500
0
500
170 320 1375 2180
1580535
Figure 13 Planshape
10
Design and construction of a windsurfer longboard
yw2
zt
05
0-1 -05 0 05 1
1
Figure 14 Spline defining the deck and rail normalised curve
x=100
x=250
x=500
x=750
x=1000
x=1500
x=1900
x=750
x=1000
x=1500
x=1900
z 100
150
200
50
0-350 -250 -150 -50 y 50 150 250 350
Figure 15 Individual cross sectional profiles for the back half of the board Noteconstant vee of 1o Note in these figures Irsquom really plotting zminus ρ ie Irsquom not includingthe effect of the rocker which would shift each successive curve upwards as you moveforward along the board
x=2000
x=2500
x=3000
x=3250
x=3500
x=3600
x=3700
x=3750
x=3250
z 100
150
200
50
0-350 -250 -150 -50 y 50 150 250 350
Figure 16 Individual cross sectional profiles for the front half of the board Noteconstant vee of 1o
11
Design and construction of a windsurfer longboard
18 Design weight
Summarising the design volume and total surface area are
Volume = 252 l and Area = 45 m2
The construction will be carbon sandwich with the following layup 200 gmminus2 car-bon fibre then high density foam (HDF) 80 gmminus3 with a thickness of 5 mm then anothercarbon layer (200gmminus2) Epoxy resin will be used and assuming a fibre to resin ratio of40 60 (see FGI data) then each layer of carbon will require 300 gmminus2 of resin Hencean individual carbon lamination will weigh 500 gmminus2 (note FGI quotes 480) The HDFwill add 80times 5times 10minus3 = 400 gmminus2 So HDF sandwiched between two layers of carbonthe skin weight is 45times (2times 500 + 400) gmminus2 which gives a total of
carbon sandwich weight = 63 kg
The core is low density polystyrene with a density of 14 kgmminus3 which gives a
core weight = 0252times 14 = 35 kg
and hence the subtotal of board without fittings and paint is 98 kgThe other components are estimated to weigh
bull centreboard case 12 kg (HDF carbon construction)
bull Mast track 11 kg (055 kg RSX part +055 kg for reinforcements)
bull Fin Box 06 kg (Tuttle std and reinforcements)
bull Footstrap plugs (times12) 04 kg
bull Fibre patches around fitting 05 kg (1 m2)
So total weight of fittings is 38 kg1 For filling and painting the estimates are
Filler =02 kgPaint =05 kg maximum estimate assuming 1 litres of paint
Hencetotal weight = 143 kg
excluding centreboard (which weighs 085 kg) footstraps amp finNote an additional full lamination adds 10Y g where Y is the fibre weight is gmminus2
ie 130 gmminus2 glass fibre adds a further 13 kg For comparison the claimed weightsof currently available production boards are Starboard Phantom 139 kg Exocet Warp135 kg and Mistral One Design 155 kg
1will lose about 35 kg when polystyrene is routed out
Table 12 lists the actual costs of the materials that go into the board If you where tobuild in glass only you could probably get it down to $1300 There is excess HDF but2 sheets isnrsquot quite enough There is also the cost of consumables
bull paint brushes rollers
bull sandpaper
bull masking tape
bull gloves masks
bull material for templates
bull measuring beakers
I didnrsquot keep track of the cost of the consumables but itrsquos of the order $100 The othercosts include footstraps which for a the full 8 straps at $25 each would be $200 (luckilyI had some old ones I could use) and a fin $150 One thing I hadnrsquot factored in was theuniextension I tried to adapt an existing uni by replacing the pin to suit the rsx trackbut it seems the pin is unique to the rsx track so I could not source a suitable pin Inthe end I had to buy a new rsx mastfoot which was incompatible with my extensionstherefore a new extension too all up another $120
I have not included the cost of any tools I had to buy eg sur-form set-square andany of the electronics associated with the vacuum pump and hotwire
Table 12 Actual material costs in Australian dollars August 2008 For comparisonExocet Warp 380 raceboard $3500 Starboard formula $3150 Starboard Futura (freerideboard) $2500 or Neil Pryde X9 - 490cm mast $1600 For the complete board also factorin footstraps and fin and possibly the unimast extension These items take the costto around $2000 which is more than a Exocet Kona My point is you have to have acompelling reason to build it yourself other than cost
110 Time required to build
This was the most challenging aspect and I would advise anyone thinking of buildingto realistically consider whether they have the time available to complete the projectFor me the project changed from being enjoyable to a chore at about the 75 completemark When this happens you tend to start rushing and trying to take short cuts
I made the first hotwire cut on 29 September and applied the last coat of paint on8 November Prior to starting the board Irsquod made the centre board centre board boxmast track box and finbox reinforcement I worked on these bits and pieces over about6 months on and off Also factor in the time to make the templates The following isroughly how much time was spent on each step I estimate at least 100 hours of labourmaybe closer to 200 hours
Job When DaysBuilding the centreboard Sporadically 2-3 weekendsfittings amp templatesHotwire cutting and board shaping Weekend 2 full daysLaminating 80 done Week off work amp weekend 7 full daysFinal deck top lamination Weekend 1 full dayFilling the weave and sanding Weekend 2 part daysMore surface prep Week nights 1 day equivalentPainting amp fitting gaskets melb cup 4 day long weekend couple hrsdayMore painting Before and after work 1 day equivalentFinish painting Weekend 1 full day
14
Chapter 2Centreboard
21 Design of centreboard
The physics of the flow around an aerofoil is not trivial Motivated by the desire forefficient and fast flight a great deal of scientific and engineering research has beendevoted to the problem Methods for predicting the performance of aerofoils involveapproximations which are quite accurate at low angles of attack more challenging ispredicting the stall characteristics
In designing the centreboard there are two main aspects to consider
1 the aerofoil section which includes the maximum thickness of the aerofoil andpoint of maximum thickness
2 the plan shape
Since the centreboard is a symmetric aerofoil camber and twist are zero and the para-metric design space is somewhat reduced A considerable effort can be devoted to thedesign process However it is worth keeping in mind that hand shaping techniqueswill ultimately limit your ability to accurate produce it
211 Aerofoil section
Based on wind tunnel experiments a large database of aerofoil characteristics was com-plied in the 1930rsquos by NACA (National Advisory Committee of Aeronautics nowNASA) Figure 21 shows the what is referred to as the NACA0010 aerofoil sectionThe important parameter is the maximum thickness of this aerofoil which in this caseis 10 of the chord length c (hence the 10 in NACA0010 00 means no camber) Notethe chord is the straight line joining the leading edge to the trailing edge The numbersin figure 21 refer to selected x y (mm) coordinates on the upper surface relative to theorigin at the leading edge where in this example the chord c = 170 mm which is thechord length at the root of the aerofoil (ie at the point where the centreboard is againstthe hull) Left of the vertical red line is where I used the balsa wood moulding whichjust happened to fit the NACA0010 profile quite well The maximum thickness of theaerofoil is at x = 51 mm where y = t2 = 85 and hence t = 17 mm (ie 10 of c)where t is the thickness
Figure 21 The NACA0010 aerofoil section plotted for a chord length of 170 mm Thisfigure is to scale and can be used as a template if you print the page at 100 scale
Figure 22 Contour plot of what we want to achieve with hand tools and limited skillthis is a challenge
As will be seen in the next section we will choose an elliptic planform so that thechord length progressively reduces towards the tip of the centreboard This meanswe must continuously scale down the profile in figure 21 Figure 22 shows the sur-face contour of the centreboard required to achieve a NACA0010 section at all crosssections
212 Planshape
Mathematical analysis of wings is difficult However a classic result obtained in the1930rsquos is that for unswept wings an elliptical planform gives the minimum possibledrag for a given value of lift (ie it achieves the best LiftDrag ratio) So why notuse the elliptical planform if nothing else it looks better than a rectangular shapedcentreboard
22 Construction of centreboard
The centreboard is built using laminated cedar strips wrapped in a layer of carbonglassfibre using epoxy as the resin There are several useful articles on design and construc-tion of centreboard on the Internet (see for example Philrsquos Foils amp Composites MothHardware Phil Stevenson and Design and construction of centreboards and rudders PaulZander )
I used a rough-sawn cedar weather-board and ripped strips of around 35 mm wideSince I was cutting from a weather-board I could rip pieces of different thickness andbuild up a coarse approximation to the final aerofoil section The strips were gluedwith epoxy For the leading edge I used a piece of balsa around 12 mm wide whichwas pre-shaped into an aerofoil leading edge (try a model aircraft shop)
The centreboard is shaped using an electrical sander with coarse sandpaper I onlymade a template of the root sectional profile So at the end of this stage I had a rectan-
16
Design and construction of a windsurfer longboard
Figure 23 Cedar strips (approx 35 mm wide) and rounded balsa lead leading edge
Figure 24 After laminating a layer of carbonglass
gular planform with a constant sectional profile Next I cut the elliptic planform witha jigsaw The aerofoil section needs to be progressively thinned down towards the tip(ie trying to keep the ratio lc constant to achieve the contour of figure 22) To dothis accurately yoursquod need several sectional profiles for several different locations Inthe end I couldnrsquot be bothered with trying to accurately produce figure 22 and justthinned it out by eye Figure 23 shows the centreboard at this point low spots andimperfects have been filled (pink coloured epoxy filler)
After cutting the required shape of the area that goes through the board itrsquos readyto be laminated I used 200 gmminus2 carbon fibre double thickness from the handle toaround 50 mm below the root I ended up adding an extra layer of glass (130 gmminus2) asI thought Irsquod used too much resin and wanted to soak it up I did it all in one go andwrapped it in a vacuum bag and held it under vacuum overnight while it dried Thevacuum isnrsquot essential but does improve the result A photo of the centreboard afterremoving from the vacuum bag is shown in figure 24 the excess fibre on the trailingedge is easily trimmed off with a knife and sanded smooth donrsquot make it razor shape
23 Centreboard Box
The centreboard is highly loaded when working to windward Therefore it is necessaryto reinforce the board at the location of the centreboard I chose to build what I call acentreboard box which serves the same role as the fin box that is it provides structuralsupport for the lateral loading The difference between a fin box and centreboard boxapart from size is that the centreboard box must also provide a pivot point and asufficient cavity for the centreboard to fit in when in the retracted position The side
17
Design and construction of a windsurfer longboard
walls of the box are made of 25 mm thick polyurethane foam with 2 sheets of HDFlaminate onto the surface (between each layer of foam is 130 gmminus2 glass) To providea pivot point a 5 mm thick piece of marine ply is used with a channel cut into it Thispiece is plywood is recessed into the top HDF layer which also has a channel cut intoit Figure 25 shows the foam and plywood layup and figure 26 shows details of thepivot point prior to the final lamination The final lamination is made up of a layer of200gmminus2 carbon and a layer of 130 gmminus2 glass
180 mm
25 mm urethane foam
5 mm PVC5 mm plywood
1000 mm
Figure 25 Layup of sidewall panels for centreboard box
Figure 26 Plywood reinforcement provides support for centreboard pivot
The width of the centreboard box cavity is asymp 25 mm and chocks of foam 25 mmthick are glued in between the side wall panels At the front of the box I used a trian-gular shaped piece of HDF and at the rear I used polyurethane foam shaped to followthe shape of the trailing edge of the centreboard figure 27These chocks of foam werefirst laminated with fibreglass before gluing them in between the side panels Afterusing the board a few times I discovered a small leak at the rear of the box between thecentral piece of foam and the sidewalls so Irsquod recommend also laying a layer of fibre-glass over the join By sanding or building up the strips you can adjust the amount offriction holding the centreboard
Layers of
HDF foam 25 mmpolyurethane
foam
Figure 27 Foam panels placed in between the sidewall panels
Ideally the centreboard should be a firm fit in the box otherwise when in the re-tracted position it has a tendency to flop back down particularly when bouncing over
18
Design and construction of a windsurfer longboard
Figure 28 Centre board box bottom view
pivot pin of centreboard
Deck
sidewall panel
friction strip
Figure 29 Friction strip which fits in the channel in the centreboard box
choppy waters Unless you are able to achieve high tolerances when manufacturingcentreboard box it is difficult to achieve a tight fit without having the centreboard jamwhen it is rotating It is better to leave some clearance in the centreboard box then packthe centreboard tight with what I call ldquofriction stripsrdquo These are simply strips about5 mm thick which are placed in the rebatted channel (shown in figure 26) after the cen-treboard is in place Initially I used plywood but found it wore out quickly so I endedup using sections from a sail batten built up to the required thickness with layers ofcarbon fibre and shown in figure 29 The strips are screwed down to the deck of theboard Make sure you place an adequate screw plug in the board Make the strips longenough so that they are in contact with the centreboard pivot pin figure 29
19
Chapter 3Mast track fin-box and footstrap plugs
When placing fittings into the board it is important to reinforce the board around thefitting using a higher density foam than the polystyrene core My approach was tobuild up a block of foam around each fitting I used 25 mm polyurethane 5 mm HDFand fibreglass to make sandwich panels that go around each part These panels helpspread the load and increase the top surface area of each part so there is more areafor the deck or hull lamination to adhere to I prepared all these parts before I startedbuilding the actual board This gave me practise in vacuum bagging on a small scale
31 Mast track
The part I had most difficulty getting was the sliding mast track I was quoted $200 fora mistral one-design track or $80 for a RSX track I opted for the RSX the only draw-back is that they donrsquot have as much travel as a traditional raceboard track figure 31Figure 32 shows the mast-track-box made out of high density foam The actual trackis screwed into the channel I used footstrap plugs as the anchor points for the screws
Figure 31 RSX mast track
32 Finbox and Footstrap plugs
I used a standard tuttle finbox You may wish to use a deep one instead but I believeformula style fins (or a fin gt 50 cm) are unnecessary for longboards so a standardshould do Foam sandwich panels are packed around the finbox and footstrap plugsto provide reinforcement figure 33
20
Design and construction of a windsurfer longboard
Figure 32 Mast track box made of urethaneHDFfibre sandwich
Figure 33 Finbox and footstrap plug reinforcements made of urethaneHDFfibresandwich
21
Chapter 4Board Construction
41 Shaping
The board is shaped as much as possible using a hotwire cutter Since the hotwire is astraight wire you cannot shaped doubly curved surfaces with it eg rails and deck forthese areas I shaped with sandpaper The sequence of shaping is as follows
1 hotwire cut rocker
2 hotwire cut vee
3 hotwire cut planshape
4 hotwire cut linear approximation of rail profile
5 hand sand deck and rail to required curve
The idea is to do as much shaping with a hotwire using templates to guide the cutEven when it came to fairing in the deck and rails I used cardboard templates of thecurve
411 Templates
I used A3 paper to print out templates of the centre-line profile (ie rocker) and plan-shape When creating these templates I subtracted the thickness of the HDF foam offthe template outline so that the specifications given earlier are for the built board notthe core To plot the profiles in full scale I used the vector graphics language AsymptoteSince an A3 piece of paper is 594times 420 mm I printed a section of the profile on eachpage then joined them all together These are the pdf files containing the templates
bull core-centre-linepdf
bull planshape-portpdf
bull planshape-starpdf 1
1Note the maximum half-width of the board is wider than an A3 sheet of paper so the planshape inthese files is referenced to a line offset 25 mm from the centre-line
22
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Preface
The following began as my working notes when designing a windsurfer I recentlybuilt Irsquod do a bit of the design leave it come back to it and forget what Irsquod done andwhich design I was going with Therefore these notes were written primary to remindme of what I did Once I started building it I decided to continue the documentationjust in case I was every crazy enough to do it again
The design was from scratch and this was my first attempt at building a windsurferIrsquod done small repairs before and built a canoe using a mould so had some prior fibre-glassing experience but had not done any vacuum bagging
The notes are not a step-by-step how-to More importantly they are based on a firsttime backyard board builders experience Irsquom sure there are many things I did whichcould be improved or done entirely differently There is not that much info on design-ing and building a windsurfer However info on building surfboards canoes sailingboats is more plentifully and can be useful The best reference that gives detailed stepby step information for windsurfers was at the website httpwwwecboardscouk Itis titled Building a composite windsurfer and gave details on building a speed board Ifound any info provided on the web to be invaluable hence I decided to put these notesout there for anyone else attempting a similar project
Before embarking on building a board you have to ask the question why If it isto save money donrsquot do it The material costs equated to roughly half the retail priceof on equivalent board However if you factor in labour therersquos certainly no savingsRealistically it was equivalent to a month full time I took 6 days off work and spent thebest part of a month worth of weekends on it It took far longer than I had anticipatedThis is partly because it was my first time and I was learning as I went Irsquod make smallmistakes which then took time to fix
For me the motivation behind the project started with an old raceboard that wasleaking Irsquod previously fixed the centre board box and suspected it was leaking SoI took the drastic step of cutting a 1times 01 m slot down the middle of the board andrebuilt the centre box It turned out there was no water there however there was watergetting in the front The board was already 18 kg and with more major repairs wouldbe getting close to 20 kg also it was 20 years old Time for a new or better 2nd-handboard Only problem is new boards of this kind are hard to get Exocet and Starboardhave started making them and Mistral appears to resurrecting the equipe On the 2nd-hand market a couple of boards appear every 12 months Australia wide So with thecentre board box built and some vacuum bagging skills acquired I decided to go all theway and build from scratch I also liked the idea of designing and building myself
Would I do it again Probably not Overall I was happy with the result Whileitrsquos obviously an amateur build it came out under weight and without any flaws thatwould effect performance Basically this is my light wind ldquosailingrdquo board maybe Irsquollgive racing a go but it wasnrsquot build with that in mind Irsquod tried wide-style early planersbut found them a bit one-dimensional My biggest sail is 85m2 which on a 85cm wideboard gives me planing threshold of sim 8 knots minimum (ie realistically a ldquosteadyrdquowind averaging 10knots) But if itrsquos a summerrsquos day with an average 8 knots Irsquod betempted to venture out and end up struggling in the lulls So I experimented with anold raceboard and found I was having heaps more fun in the 8-12knots winds
Contents
1 Board design 511 Maximum dimensions 512 Rocker profile 513 Deck centre-line profile 614 Vee concaves tail kick 615 Planshape 616 Deck cross section and rails 617 Data files 718 Design weight 1219 Material costs 13110 Time required to build 14
2 Centreboard 1521 Design of centreboard 15
211 Aerofoil section 15212 Planshape 16
22 Construction of centreboard 1623 Centreboard Box 17
3 Mast track fin-box and footstrap plugs 2031 Mast track 2032 Finbox and Footstrap plugs 20
4 Board Construction 2241 Shaping 22
411 Templates 22412 Core 23413 Rocker and deck 23414 Vee 23415 Planshape 23416 Rails 23
42 Laminating 24421 CarbonHDF to bottom 28422 CarbonHDF to deck 29423 Fitting the fittings 29
5 The finished product 3551 Photos from Inverloch 25042010 39
A Tooling 44A1 Compressor 44A2 Vacuum controller 44A3 Hotwire cutter 46A4 Hotwire voltage control 46
B References and links 49
4
Chapter 1Board design
11 Maximum dimensions
maximum length = l = 3800 mmmaximum width = wm = 640 mmmaximum thickness = tm = 180 mm
12 Rocker profile
The bottom rocker profile ρ (in mm) is defined by the equation
ρ(x) =
0 x lt 800
(xminus 800)4
3times 1011 x gt 800(11)
where x (in mm) is the lengthwise coordinate and ρ is measured relative to the hori-zontal datum z = 0 where z is the vertical coordinate as defined in figure 11 Henceat the stern of the board (ie for x lt 800 mm) the rocker is a true flat Forward ofx = 800 mm the rocker is defined by a quartic giving a maximum rocker value at thebow of the board of ρ = 270 mm The quartic curve generates very little rocker initiallyitrsquos only around x = 2000 m that the rocker starts to kick in
Actually the rocker profile given by (11) can be expressed in terms of two inde-pendent parameters the maximum rocker ρm and the coordinate where the rockerbegins x f Rewriting (11) in terms of these two parameters gives
ρ(x) =
0 x lt x f
ρm
(xminus x f
l minus x f
)4
x gt x f(12)
where l is the maximum length
5
Design and construction of a windsurfer longboard
13 Deck centre-line profile
The deck profile was generated by sketching a spline keeping in mind I didnrsquot wantthe trailing edge of the centreboard to protrude through the deck when it was in theretracted position The centreboard has a maximum chord of 170 mm so the maximumthickness of the board was set to 180 mm
14 Vee concaves tail kick
The reference board I used during the design was heavily concaved figure 12 Irsquom notsure how one would accurately shape these contours In any case most modern boardsseem to have abandoned concaves A simple vee should do the job of counteracting theslapping tendency of a flat hull which concaves also serve to do Concaves may assistis lateral resistance but probably add drag there seems to be very little information ontheir effect In the end I decided to go for a small amount of vee only no tail kick orconcaves The actual vee is constant at 1 degree along the full length
15 Planshape
Figure 13 shows the planshape of the bottom of the board The rails are parallel forapproximately the range x = 1700 to x = 2100 mm where the width is the maximumvalue wm = 640 mm The planshape was generated by a spline sketch and hencecannot be represented in equation form although its not far off an ellipse
16 Deck cross section and rails
Finally the deck and rail profiles are required to completely specify the geometry ofthe board Raceboards have sharp rails which run almost the complete length of theboard This feature greatly simplifies the design since one cross sectional profile canbe specified and simply scaled appropriately based on the thickness and width of theboard at a given x coordinate I played around with using quadratics arcs and thelike to define the cross section but in the end it was simpler just to sketch a spline thatlooked about right Figure 14 shows the normalised cross section used for all locationsIrsquoll probably knock the corner off this profile near the nose of the board where sharprails are more of a liability
Individual cross sectional profiles for the back half of the board are shown in fig-ure 15 and for the front half of the board in figure 16 The area bounded by theindividual cross sections can be calculated by numerically integrating the curves andhence the volume of the board is calculated from the summation
V = A1∆x1 + A2∆x2 + A3∆x3 + + An∆xn =n
sumi
Ai∆xi
where Ai is the area of the ith cross section and ∆xi is the ldquothicknessrdquo of the crosssection slice For the data given above the volume turns out to be
V = 252 litres
6
Design and construction of a windsurfer longboard
The surface area of the board can be found by calculating the length of individuallines show in figures 15 and 16 For the deck and rails this length is given by integrat-ing the upper curves using the formula
S =int w2
minusw2
radic1 +
(dzdy
)2
dy
If this is done for many x locations on the board then the surface area is given by thesummation
A =n
sumi
Si∆xi = 256 m2 deck and rails
A similar calculation can by done for the bottom of the board but it is much simplersince the lines are straight and at a given x location
S =w
cos θ
where θ is the vee angle which is small and hence S asymp w so
A =int 3800
0w dx = 195 m2 bottom
where w is the width of the board which is a function of x
17 Data files
Plain text files containing the coordinates for the
Figure 12 The board used as a rough guide for the design The actual board I designedis quite different the only dimension I matched was the maximum rocker (nose kick)Itrsquos good to have something to reference your design against just to ensure you donrsquotdesign something ldquooff the scalerdquo
9
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
x (mm)
0
y (mm)
l = 3800mm
w
Stern
500 1000 1500 2000 2500 3000 3500-500
0
500
170 320 1375 2180
1580535
Figure 13 Planshape
10
Design and construction of a windsurfer longboard
yw2
zt
05
0-1 -05 0 05 1
1
Figure 14 Spline defining the deck and rail normalised curve
x=100
x=250
x=500
x=750
x=1000
x=1500
x=1900
x=750
x=1000
x=1500
x=1900
z 100
150
200
50
0-350 -250 -150 -50 y 50 150 250 350
Figure 15 Individual cross sectional profiles for the back half of the board Noteconstant vee of 1o Note in these figures Irsquom really plotting zminus ρ ie Irsquom not includingthe effect of the rocker which would shift each successive curve upwards as you moveforward along the board
x=2000
x=2500
x=3000
x=3250
x=3500
x=3600
x=3700
x=3750
x=3250
z 100
150
200
50
0-350 -250 -150 -50 y 50 150 250 350
Figure 16 Individual cross sectional profiles for the front half of the board Noteconstant vee of 1o
11
Design and construction of a windsurfer longboard
18 Design weight
Summarising the design volume and total surface area are
Volume = 252 l and Area = 45 m2
The construction will be carbon sandwich with the following layup 200 gmminus2 car-bon fibre then high density foam (HDF) 80 gmminus3 with a thickness of 5 mm then anothercarbon layer (200gmminus2) Epoxy resin will be used and assuming a fibre to resin ratio of40 60 (see FGI data) then each layer of carbon will require 300 gmminus2 of resin Hencean individual carbon lamination will weigh 500 gmminus2 (note FGI quotes 480) The HDFwill add 80times 5times 10minus3 = 400 gmminus2 So HDF sandwiched between two layers of carbonthe skin weight is 45times (2times 500 + 400) gmminus2 which gives a total of
carbon sandwich weight = 63 kg
The core is low density polystyrene with a density of 14 kgmminus3 which gives a
core weight = 0252times 14 = 35 kg
and hence the subtotal of board without fittings and paint is 98 kgThe other components are estimated to weigh
bull centreboard case 12 kg (HDF carbon construction)
bull Mast track 11 kg (055 kg RSX part +055 kg for reinforcements)
bull Fin Box 06 kg (Tuttle std and reinforcements)
bull Footstrap plugs (times12) 04 kg
bull Fibre patches around fitting 05 kg (1 m2)
So total weight of fittings is 38 kg1 For filling and painting the estimates are
Filler =02 kgPaint =05 kg maximum estimate assuming 1 litres of paint
Hencetotal weight = 143 kg
excluding centreboard (which weighs 085 kg) footstraps amp finNote an additional full lamination adds 10Y g where Y is the fibre weight is gmminus2
ie 130 gmminus2 glass fibre adds a further 13 kg For comparison the claimed weightsof currently available production boards are Starboard Phantom 139 kg Exocet Warp135 kg and Mistral One Design 155 kg
1will lose about 35 kg when polystyrene is routed out
Table 12 lists the actual costs of the materials that go into the board If you where tobuild in glass only you could probably get it down to $1300 There is excess HDF but2 sheets isnrsquot quite enough There is also the cost of consumables
bull paint brushes rollers
bull sandpaper
bull masking tape
bull gloves masks
bull material for templates
bull measuring beakers
I didnrsquot keep track of the cost of the consumables but itrsquos of the order $100 The othercosts include footstraps which for a the full 8 straps at $25 each would be $200 (luckilyI had some old ones I could use) and a fin $150 One thing I hadnrsquot factored in was theuniextension I tried to adapt an existing uni by replacing the pin to suit the rsx trackbut it seems the pin is unique to the rsx track so I could not source a suitable pin Inthe end I had to buy a new rsx mastfoot which was incompatible with my extensionstherefore a new extension too all up another $120
I have not included the cost of any tools I had to buy eg sur-form set-square andany of the electronics associated with the vacuum pump and hotwire
Table 12 Actual material costs in Australian dollars August 2008 For comparisonExocet Warp 380 raceboard $3500 Starboard formula $3150 Starboard Futura (freerideboard) $2500 or Neil Pryde X9 - 490cm mast $1600 For the complete board also factorin footstraps and fin and possibly the unimast extension These items take the costto around $2000 which is more than a Exocet Kona My point is you have to have acompelling reason to build it yourself other than cost
110 Time required to build
This was the most challenging aspect and I would advise anyone thinking of buildingto realistically consider whether they have the time available to complete the projectFor me the project changed from being enjoyable to a chore at about the 75 completemark When this happens you tend to start rushing and trying to take short cuts
I made the first hotwire cut on 29 September and applied the last coat of paint on8 November Prior to starting the board Irsquod made the centre board centre board boxmast track box and finbox reinforcement I worked on these bits and pieces over about6 months on and off Also factor in the time to make the templates The following isroughly how much time was spent on each step I estimate at least 100 hours of labourmaybe closer to 200 hours
Job When DaysBuilding the centreboard Sporadically 2-3 weekendsfittings amp templatesHotwire cutting and board shaping Weekend 2 full daysLaminating 80 done Week off work amp weekend 7 full daysFinal deck top lamination Weekend 1 full dayFilling the weave and sanding Weekend 2 part daysMore surface prep Week nights 1 day equivalentPainting amp fitting gaskets melb cup 4 day long weekend couple hrsdayMore painting Before and after work 1 day equivalentFinish painting Weekend 1 full day
14
Chapter 2Centreboard
21 Design of centreboard
The physics of the flow around an aerofoil is not trivial Motivated by the desire forefficient and fast flight a great deal of scientific and engineering research has beendevoted to the problem Methods for predicting the performance of aerofoils involveapproximations which are quite accurate at low angles of attack more challenging ispredicting the stall characteristics
In designing the centreboard there are two main aspects to consider
1 the aerofoil section which includes the maximum thickness of the aerofoil andpoint of maximum thickness
2 the plan shape
Since the centreboard is a symmetric aerofoil camber and twist are zero and the para-metric design space is somewhat reduced A considerable effort can be devoted to thedesign process However it is worth keeping in mind that hand shaping techniqueswill ultimately limit your ability to accurate produce it
211 Aerofoil section
Based on wind tunnel experiments a large database of aerofoil characteristics was com-plied in the 1930rsquos by NACA (National Advisory Committee of Aeronautics nowNASA) Figure 21 shows the what is referred to as the NACA0010 aerofoil sectionThe important parameter is the maximum thickness of this aerofoil which in this caseis 10 of the chord length c (hence the 10 in NACA0010 00 means no camber) Notethe chord is the straight line joining the leading edge to the trailing edge The numbersin figure 21 refer to selected x y (mm) coordinates on the upper surface relative to theorigin at the leading edge where in this example the chord c = 170 mm which is thechord length at the root of the aerofoil (ie at the point where the centreboard is againstthe hull) Left of the vertical red line is where I used the balsa wood moulding whichjust happened to fit the NACA0010 profile quite well The maximum thickness of theaerofoil is at x = 51 mm where y = t2 = 85 and hence t = 17 mm (ie 10 of c)where t is the thickness
Figure 21 The NACA0010 aerofoil section plotted for a chord length of 170 mm Thisfigure is to scale and can be used as a template if you print the page at 100 scale
Figure 22 Contour plot of what we want to achieve with hand tools and limited skillthis is a challenge
As will be seen in the next section we will choose an elliptic planform so that thechord length progressively reduces towards the tip of the centreboard This meanswe must continuously scale down the profile in figure 21 Figure 22 shows the sur-face contour of the centreboard required to achieve a NACA0010 section at all crosssections
212 Planshape
Mathematical analysis of wings is difficult However a classic result obtained in the1930rsquos is that for unswept wings an elliptical planform gives the minimum possibledrag for a given value of lift (ie it achieves the best LiftDrag ratio) So why notuse the elliptical planform if nothing else it looks better than a rectangular shapedcentreboard
22 Construction of centreboard
The centreboard is built using laminated cedar strips wrapped in a layer of carbonglassfibre using epoxy as the resin There are several useful articles on design and construc-tion of centreboard on the Internet (see for example Philrsquos Foils amp Composites MothHardware Phil Stevenson and Design and construction of centreboards and rudders PaulZander )
I used a rough-sawn cedar weather-board and ripped strips of around 35 mm wideSince I was cutting from a weather-board I could rip pieces of different thickness andbuild up a coarse approximation to the final aerofoil section The strips were gluedwith epoxy For the leading edge I used a piece of balsa around 12 mm wide whichwas pre-shaped into an aerofoil leading edge (try a model aircraft shop)
The centreboard is shaped using an electrical sander with coarse sandpaper I onlymade a template of the root sectional profile So at the end of this stage I had a rectan-
16
Design and construction of a windsurfer longboard
Figure 23 Cedar strips (approx 35 mm wide) and rounded balsa lead leading edge
Figure 24 After laminating a layer of carbonglass
gular planform with a constant sectional profile Next I cut the elliptic planform witha jigsaw The aerofoil section needs to be progressively thinned down towards the tip(ie trying to keep the ratio lc constant to achieve the contour of figure 22) To dothis accurately yoursquod need several sectional profiles for several different locations Inthe end I couldnrsquot be bothered with trying to accurately produce figure 22 and justthinned it out by eye Figure 23 shows the centreboard at this point low spots andimperfects have been filled (pink coloured epoxy filler)
After cutting the required shape of the area that goes through the board itrsquos readyto be laminated I used 200 gmminus2 carbon fibre double thickness from the handle toaround 50 mm below the root I ended up adding an extra layer of glass (130 gmminus2) asI thought Irsquod used too much resin and wanted to soak it up I did it all in one go andwrapped it in a vacuum bag and held it under vacuum overnight while it dried Thevacuum isnrsquot essential but does improve the result A photo of the centreboard afterremoving from the vacuum bag is shown in figure 24 the excess fibre on the trailingedge is easily trimmed off with a knife and sanded smooth donrsquot make it razor shape
23 Centreboard Box
The centreboard is highly loaded when working to windward Therefore it is necessaryto reinforce the board at the location of the centreboard I chose to build what I call acentreboard box which serves the same role as the fin box that is it provides structuralsupport for the lateral loading The difference between a fin box and centreboard boxapart from size is that the centreboard box must also provide a pivot point and asufficient cavity for the centreboard to fit in when in the retracted position The side
17
Design and construction of a windsurfer longboard
walls of the box are made of 25 mm thick polyurethane foam with 2 sheets of HDFlaminate onto the surface (between each layer of foam is 130 gmminus2 glass) To providea pivot point a 5 mm thick piece of marine ply is used with a channel cut into it Thispiece is plywood is recessed into the top HDF layer which also has a channel cut intoit Figure 25 shows the foam and plywood layup and figure 26 shows details of thepivot point prior to the final lamination The final lamination is made up of a layer of200gmminus2 carbon and a layer of 130 gmminus2 glass
180 mm
25 mm urethane foam
5 mm PVC5 mm plywood
1000 mm
Figure 25 Layup of sidewall panels for centreboard box
Figure 26 Plywood reinforcement provides support for centreboard pivot
The width of the centreboard box cavity is asymp 25 mm and chocks of foam 25 mmthick are glued in between the side wall panels At the front of the box I used a trian-gular shaped piece of HDF and at the rear I used polyurethane foam shaped to followthe shape of the trailing edge of the centreboard figure 27These chocks of foam werefirst laminated with fibreglass before gluing them in between the side panels Afterusing the board a few times I discovered a small leak at the rear of the box between thecentral piece of foam and the sidewalls so Irsquod recommend also laying a layer of fibre-glass over the join By sanding or building up the strips you can adjust the amount offriction holding the centreboard
Layers of
HDF foam 25 mmpolyurethane
foam
Figure 27 Foam panels placed in between the sidewall panels
Ideally the centreboard should be a firm fit in the box otherwise when in the re-tracted position it has a tendency to flop back down particularly when bouncing over
18
Design and construction of a windsurfer longboard
Figure 28 Centre board box bottom view
pivot pin of centreboard
Deck
sidewall panel
friction strip
Figure 29 Friction strip which fits in the channel in the centreboard box
choppy waters Unless you are able to achieve high tolerances when manufacturingcentreboard box it is difficult to achieve a tight fit without having the centreboard jamwhen it is rotating It is better to leave some clearance in the centreboard box then packthe centreboard tight with what I call ldquofriction stripsrdquo These are simply strips about5 mm thick which are placed in the rebatted channel (shown in figure 26) after the cen-treboard is in place Initially I used plywood but found it wore out quickly so I endedup using sections from a sail batten built up to the required thickness with layers ofcarbon fibre and shown in figure 29 The strips are screwed down to the deck of theboard Make sure you place an adequate screw plug in the board Make the strips longenough so that they are in contact with the centreboard pivot pin figure 29
19
Chapter 3Mast track fin-box and footstrap plugs
When placing fittings into the board it is important to reinforce the board around thefitting using a higher density foam than the polystyrene core My approach was tobuild up a block of foam around each fitting I used 25 mm polyurethane 5 mm HDFand fibreglass to make sandwich panels that go around each part These panels helpspread the load and increase the top surface area of each part so there is more areafor the deck or hull lamination to adhere to I prepared all these parts before I startedbuilding the actual board This gave me practise in vacuum bagging on a small scale
31 Mast track
The part I had most difficulty getting was the sliding mast track I was quoted $200 fora mistral one-design track or $80 for a RSX track I opted for the RSX the only draw-back is that they donrsquot have as much travel as a traditional raceboard track figure 31Figure 32 shows the mast-track-box made out of high density foam The actual trackis screwed into the channel I used footstrap plugs as the anchor points for the screws
Figure 31 RSX mast track
32 Finbox and Footstrap plugs
I used a standard tuttle finbox You may wish to use a deep one instead but I believeformula style fins (or a fin gt 50 cm) are unnecessary for longboards so a standardshould do Foam sandwich panels are packed around the finbox and footstrap plugsto provide reinforcement figure 33
20
Design and construction of a windsurfer longboard
Figure 32 Mast track box made of urethaneHDFfibre sandwich
Figure 33 Finbox and footstrap plug reinforcements made of urethaneHDFfibresandwich
21
Chapter 4Board Construction
41 Shaping
The board is shaped as much as possible using a hotwire cutter Since the hotwire is astraight wire you cannot shaped doubly curved surfaces with it eg rails and deck forthese areas I shaped with sandpaper The sequence of shaping is as follows
1 hotwire cut rocker
2 hotwire cut vee
3 hotwire cut planshape
4 hotwire cut linear approximation of rail profile
5 hand sand deck and rail to required curve
The idea is to do as much shaping with a hotwire using templates to guide the cutEven when it came to fairing in the deck and rails I used cardboard templates of thecurve
411 Templates
I used A3 paper to print out templates of the centre-line profile (ie rocker) and plan-shape When creating these templates I subtracted the thickness of the HDF foam offthe template outline so that the specifications given earlier are for the built board notthe core To plot the profiles in full scale I used the vector graphics language AsymptoteSince an A3 piece of paper is 594times 420 mm I printed a section of the profile on eachpage then joined them all together These are the pdf files containing the templates
bull core-centre-linepdf
bull planshape-portpdf
bull planshape-starpdf 1
1Note the maximum half-width of the board is wider than an A3 sheet of paper so the planshape inthese files is referenced to a line offset 25 mm from the centre-line
22
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Contents
1 Board design 511 Maximum dimensions 512 Rocker profile 513 Deck centre-line profile 614 Vee concaves tail kick 615 Planshape 616 Deck cross section and rails 617 Data files 718 Design weight 1219 Material costs 13110 Time required to build 14
2 Centreboard 1521 Design of centreboard 15
211 Aerofoil section 15212 Planshape 16
22 Construction of centreboard 1623 Centreboard Box 17
3 Mast track fin-box and footstrap plugs 2031 Mast track 2032 Finbox and Footstrap plugs 20
4 Board Construction 2241 Shaping 22
411 Templates 22412 Core 23413 Rocker and deck 23414 Vee 23415 Planshape 23416 Rails 23
42 Laminating 24421 CarbonHDF to bottom 28422 CarbonHDF to deck 29423 Fitting the fittings 29
5 The finished product 3551 Photos from Inverloch 25042010 39
A Tooling 44A1 Compressor 44A2 Vacuum controller 44A3 Hotwire cutter 46A4 Hotwire voltage control 46
B References and links 49
4
Chapter 1Board design
11 Maximum dimensions
maximum length = l = 3800 mmmaximum width = wm = 640 mmmaximum thickness = tm = 180 mm
12 Rocker profile
The bottom rocker profile ρ (in mm) is defined by the equation
ρ(x) =
0 x lt 800
(xminus 800)4
3times 1011 x gt 800(11)
where x (in mm) is the lengthwise coordinate and ρ is measured relative to the hori-zontal datum z = 0 where z is the vertical coordinate as defined in figure 11 Henceat the stern of the board (ie for x lt 800 mm) the rocker is a true flat Forward ofx = 800 mm the rocker is defined by a quartic giving a maximum rocker value at thebow of the board of ρ = 270 mm The quartic curve generates very little rocker initiallyitrsquos only around x = 2000 m that the rocker starts to kick in
Actually the rocker profile given by (11) can be expressed in terms of two inde-pendent parameters the maximum rocker ρm and the coordinate where the rockerbegins x f Rewriting (11) in terms of these two parameters gives
ρ(x) =
0 x lt x f
ρm
(xminus x f
l minus x f
)4
x gt x f(12)
where l is the maximum length
5
Design and construction of a windsurfer longboard
13 Deck centre-line profile
The deck profile was generated by sketching a spline keeping in mind I didnrsquot wantthe trailing edge of the centreboard to protrude through the deck when it was in theretracted position The centreboard has a maximum chord of 170 mm so the maximumthickness of the board was set to 180 mm
14 Vee concaves tail kick
The reference board I used during the design was heavily concaved figure 12 Irsquom notsure how one would accurately shape these contours In any case most modern boardsseem to have abandoned concaves A simple vee should do the job of counteracting theslapping tendency of a flat hull which concaves also serve to do Concaves may assistis lateral resistance but probably add drag there seems to be very little information ontheir effect In the end I decided to go for a small amount of vee only no tail kick orconcaves The actual vee is constant at 1 degree along the full length
15 Planshape
Figure 13 shows the planshape of the bottom of the board The rails are parallel forapproximately the range x = 1700 to x = 2100 mm where the width is the maximumvalue wm = 640 mm The planshape was generated by a spline sketch and hencecannot be represented in equation form although its not far off an ellipse
16 Deck cross section and rails
Finally the deck and rail profiles are required to completely specify the geometry ofthe board Raceboards have sharp rails which run almost the complete length of theboard This feature greatly simplifies the design since one cross sectional profile canbe specified and simply scaled appropriately based on the thickness and width of theboard at a given x coordinate I played around with using quadratics arcs and thelike to define the cross section but in the end it was simpler just to sketch a spline thatlooked about right Figure 14 shows the normalised cross section used for all locationsIrsquoll probably knock the corner off this profile near the nose of the board where sharprails are more of a liability
Individual cross sectional profiles for the back half of the board are shown in fig-ure 15 and for the front half of the board in figure 16 The area bounded by theindividual cross sections can be calculated by numerically integrating the curves andhence the volume of the board is calculated from the summation
V = A1∆x1 + A2∆x2 + A3∆x3 + + An∆xn =n
sumi
Ai∆xi
where Ai is the area of the ith cross section and ∆xi is the ldquothicknessrdquo of the crosssection slice For the data given above the volume turns out to be
V = 252 litres
6
Design and construction of a windsurfer longboard
The surface area of the board can be found by calculating the length of individuallines show in figures 15 and 16 For the deck and rails this length is given by integrat-ing the upper curves using the formula
S =int w2
minusw2
radic1 +
(dzdy
)2
dy
If this is done for many x locations on the board then the surface area is given by thesummation
A =n
sumi
Si∆xi = 256 m2 deck and rails
A similar calculation can by done for the bottom of the board but it is much simplersince the lines are straight and at a given x location
S =w
cos θ
where θ is the vee angle which is small and hence S asymp w so
A =int 3800
0w dx = 195 m2 bottom
where w is the width of the board which is a function of x
17 Data files
Plain text files containing the coordinates for the
Figure 12 The board used as a rough guide for the design The actual board I designedis quite different the only dimension I matched was the maximum rocker (nose kick)Itrsquos good to have something to reference your design against just to ensure you donrsquotdesign something ldquooff the scalerdquo
9
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
x (mm)
0
y (mm)
l = 3800mm
w
Stern
500 1000 1500 2000 2500 3000 3500-500
0
500
170 320 1375 2180
1580535
Figure 13 Planshape
10
Design and construction of a windsurfer longboard
yw2
zt
05
0-1 -05 0 05 1
1
Figure 14 Spline defining the deck and rail normalised curve
x=100
x=250
x=500
x=750
x=1000
x=1500
x=1900
x=750
x=1000
x=1500
x=1900
z 100
150
200
50
0-350 -250 -150 -50 y 50 150 250 350
Figure 15 Individual cross sectional profiles for the back half of the board Noteconstant vee of 1o Note in these figures Irsquom really plotting zminus ρ ie Irsquom not includingthe effect of the rocker which would shift each successive curve upwards as you moveforward along the board
x=2000
x=2500
x=3000
x=3250
x=3500
x=3600
x=3700
x=3750
x=3250
z 100
150
200
50
0-350 -250 -150 -50 y 50 150 250 350
Figure 16 Individual cross sectional profiles for the front half of the board Noteconstant vee of 1o
11
Design and construction of a windsurfer longboard
18 Design weight
Summarising the design volume and total surface area are
Volume = 252 l and Area = 45 m2
The construction will be carbon sandwich with the following layup 200 gmminus2 car-bon fibre then high density foam (HDF) 80 gmminus3 with a thickness of 5 mm then anothercarbon layer (200gmminus2) Epoxy resin will be used and assuming a fibre to resin ratio of40 60 (see FGI data) then each layer of carbon will require 300 gmminus2 of resin Hencean individual carbon lamination will weigh 500 gmminus2 (note FGI quotes 480) The HDFwill add 80times 5times 10minus3 = 400 gmminus2 So HDF sandwiched between two layers of carbonthe skin weight is 45times (2times 500 + 400) gmminus2 which gives a total of
carbon sandwich weight = 63 kg
The core is low density polystyrene with a density of 14 kgmminus3 which gives a
core weight = 0252times 14 = 35 kg
and hence the subtotal of board without fittings and paint is 98 kgThe other components are estimated to weigh
bull centreboard case 12 kg (HDF carbon construction)
bull Mast track 11 kg (055 kg RSX part +055 kg for reinforcements)
bull Fin Box 06 kg (Tuttle std and reinforcements)
bull Footstrap plugs (times12) 04 kg
bull Fibre patches around fitting 05 kg (1 m2)
So total weight of fittings is 38 kg1 For filling and painting the estimates are
Filler =02 kgPaint =05 kg maximum estimate assuming 1 litres of paint
Hencetotal weight = 143 kg
excluding centreboard (which weighs 085 kg) footstraps amp finNote an additional full lamination adds 10Y g where Y is the fibre weight is gmminus2
ie 130 gmminus2 glass fibre adds a further 13 kg For comparison the claimed weightsof currently available production boards are Starboard Phantom 139 kg Exocet Warp135 kg and Mistral One Design 155 kg
1will lose about 35 kg when polystyrene is routed out
Table 12 lists the actual costs of the materials that go into the board If you where tobuild in glass only you could probably get it down to $1300 There is excess HDF but2 sheets isnrsquot quite enough There is also the cost of consumables
bull paint brushes rollers
bull sandpaper
bull masking tape
bull gloves masks
bull material for templates
bull measuring beakers
I didnrsquot keep track of the cost of the consumables but itrsquos of the order $100 The othercosts include footstraps which for a the full 8 straps at $25 each would be $200 (luckilyI had some old ones I could use) and a fin $150 One thing I hadnrsquot factored in was theuniextension I tried to adapt an existing uni by replacing the pin to suit the rsx trackbut it seems the pin is unique to the rsx track so I could not source a suitable pin Inthe end I had to buy a new rsx mastfoot which was incompatible with my extensionstherefore a new extension too all up another $120
I have not included the cost of any tools I had to buy eg sur-form set-square andany of the electronics associated with the vacuum pump and hotwire
Table 12 Actual material costs in Australian dollars August 2008 For comparisonExocet Warp 380 raceboard $3500 Starboard formula $3150 Starboard Futura (freerideboard) $2500 or Neil Pryde X9 - 490cm mast $1600 For the complete board also factorin footstraps and fin and possibly the unimast extension These items take the costto around $2000 which is more than a Exocet Kona My point is you have to have acompelling reason to build it yourself other than cost
110 Time required to build
This was the most challenging aspect and I would advise anyone thinking of buildingto realistically consider whether they have the time available to complete the projectFor me the project changed from being enjoyable to a chore at about the 75 completemark When this happens you tend to start rushing and trying to take short cuts
I made the first hotwire cut on 29 September and applied the last coat of paint on8 November Prior to starting the board Irsquod made the centre board centre board boxmast track box and finbox reinforcement I worked on these bits and pieces over about6 months on and off Also factor in the time to make the templates The following isroughly how much time was spent on each step I estimate at least 100 hours of labourmaybe closer to 200 hours
Job When DaysBuilding the centreboard Sporadically 2-3 weekendsfittings amp templatesHotwire cutting and board shaping Weekend 2 full daysLaminating 80 done Week off work amp weekend 7 full daysFinal deck top lamination Weekend 1 full dayFilling the weave and sanding Weekend 2 part daysMore surface prep Week nights 1 day equivalentPainting amp fitting gaskets melb cup 4 day long weekend couple hrsdayMore painting Before and after work 1 day equivalentFinish painting Weekend 1 full day
14
Chapter 2Centreboard
21 Design of centreboard
The physics of the flow around an aerofoil is not trivial Motivated by the desire forefficient and fast flight a great deal of scientific and engineering research has beendevoted to the problem Methods for predicting the performance of aerofoils involveapproximations which are quite accurate at low angles of attack more challenging ispredicting the stall characteristics
In designing the centreboard there are two main aspects to consider
1 the aerofoil section which includes the maximum thickness of the aerofoil andpoint of maximum thickness
2 the plan shape
Since the centreboard is a symmetric aerofoil camber and twist are zero and the para-metric design space is somewhat reduced A considerable effort can be devoted to thedesign process However it is worth keeping in mind that hand shaping techniqueswill ultimately limit your ability to accurate produce it
211 Aerofoil section
Based on wind tunnel experiments a large database of aerofoil characteristics was com-plied in the 1930rsquos by NACA (National Advisory Committee of Aeronautics nowNASA) Figure 21 shows the what is referred to as the NACA0010 aerofoil sectionThe important parameter is the maximum thickness of this aerofoil which in this caseis 10 of the chord length c (hence the 10 in NACA0010 00 means no camber) Notethe chord is the straight line joining the leading edge to the trailing edge The numbersin figure 21 refer to selected x y (mm) coordinates on the upper surface relative to theorigin at the leading edge where in this example the chord c = 170 mm which is thechord length at the root of the aerofoil (ie at the point where the centreboard is againstthe hull) Left of the vertical red line is where I used the balsa wood moulding whichjust happened to fit the NACA0010 profile quite well The maximum thickness of theaerofoil is at x = 51 mm where y = t2 = 85 and hence t = 17 mm (ie 10 of c)where t is the thickness
Figure 21 The NACA0010 aerofoil section plotted for a chord length of 170 mm Thisfigure is to scale and can be used as a template if you print the page at 100 scale
Figure 22 Contour plot of what we want to achieve with hand tools and limited skillthis is a challenge
As will be seen in the next section we will choose an elliptic planform so that thechord length progressively reduces towards the tip of the centreboard This meanswe must continuously scale down the profile in figure 21 Figure 22 shows the sur-face contour of the centreboard required to achieve a NACA0010 section at all crosssections
212 Planshape
Mathematical analysis of wings is difficult However a classic result obtained in the1930rsquos is that for unswept wings an elliptical planform gives the minimum possibledrag for a given value of lift (ie it achieves the best LiftDrag ratio) So why notuse the elliptical planform if nothing else it looks better than a rectangular shapedcentreboard
22 Construction of centreboard
The centreboard is built using laminated cedar strips wrapped in a layer of carbonglassfibre using epoxy as the resin There are several useful articles on design and construc-tion of centreboard on the Internet (see for example Philrsquos Foils amp Composites MothHardware Phil Stevenson and Design and construction of centreboards and rudders PaulZander )
I used a rough-sawn cedar weather-board and ripped strips of around 35 mm wideSince I was cutting from a weather-board I could rip pieces of different thickness andbuild up a coarse approximation to the final aerofoil section The strips were gluedwith epoxy For the leading edge I used a piece of balsa around 12 mm wide whichwas pre-shaped into an aerofoil leading edge (try a model aircraft shop)
The centreboard is shaped using an electrical sander with coarse sandpaper I onlymade a template of the root sectional profile So at the end of this stage I had a rectan-
16
Design and construction of a windsurfer longboard
Figure 23 Cedar strips (approx 35 mm wide) and rounded balsa lead leading edge
Figure 24 After laminating a layer of carbonglass
gular planform with a constant sectional profile Next I cut the elliptic planform witha jigsaw The aerofoil section needs to be progressively thinned down towards the tip(ie trying to keep the ratio lc constant to achieve the contour of figure 22) To dothis accurately yoursquod need several sectional profiles for several different locations Inthe end I couldnrsquot be bothered with trying to accurately produce figure 22 and justthinned it out by eye Figure 23 shows the centreboard at this point low spots andimperfects have been filled (pink coloured epoxy filler)
After cutting the required shape of the area that goes through the board itrsquos readyto be laminated I used 200 gmminus2 carbon fibre double thickness from the handle toaround 50 mm below the root I ended up adding an extra layer of glass (130 gmminus2) asI thought Irsquod used too much resin and wanted to soak it up I did it all in one go andwrapped it in a vacuum bag and held it under vacuum overnight while it dried Thevacuum isnrsquot essential but does improve the result A photo of the centreboard afterremoving from the vacuum bag is shown in figure 24 the excess fibre on the trailingedge is easily trimmed off with a knife and sanded smooth donrsquot make it razor shape
23 Centreboard Box
The centreboard is highly loaded when working to windward Therefore it is necessaryto reinforce the board at the location of the centreboard I chose to build what I call acentreboard box which serves the same role as the fin box that is it provides structuralsupport for the lateral loading The difference between a fin box and centreboard boxapart from size is that the centreboard box must also provide a pivot point and asufficient cavity for the centreboard to fit in when in the retracted position The side
17
Design and construction of a windsurfer longboard
walls of the box are made of 25 mm thick polyurethane foam with 2 sheets of HDFlaminate onto the surface (between each layer of foam is 130 gmminus2 glass) To providea pivot point a 5 mm thick piece of marine ply is used with a channel cut into it Thispiece is plywood is recessed into the top HDF layer which also has a channel cut intoit Figure 25 shows the foam and plywood layup and figure 26 shows details of thepivot point prior to the final lamination The final lamination is made up of a layer of200gmminus2 carbon and a layer of 130 gmminus2 glass
180 mm
25 mm urethane foam
5 mm PVC5 mm plywood
1000 mm
Figure 25 Layup of sidewall panels for centreboard box
Figure 26 Plywood reinforcement provides support for centreboard pivot
The width of the centreboard box cavity is asymp 25 mm and chocks of foam 25 mmthick are glued in between the side wall panels At the front of the box I used a trian-gular shaped piece of HDF and at the rear I used polyurethane foam shaped to followthe shape of the trailing edge of the centreboard figure 27These chocks of foam werefirst laminated with fibreglass before gluing them in between the side panels Afterusing the board a few times I discovered a small leak at the rear of the box between thecentral piece of foam and the sidewalls so Irsquod recommend also laying a layer of fibre-glass over the join By sanding or building up the strips you can adjust the amount offriction holding the centreboard
Layers of
HDF foam 25 mmpolyurethane
foam
Figure 27 Foam panels placed in between the sidewall panels
Ideally the centreboard should be a firm fit in the box otherwise when in the re-tracted position it has a tendency to flop back down particularly when bouncing over
18
Design and construction of a windsurfer longboard
Figure 28 Centre board box bottom view
pivot pin of centreboard
Deck
sidewall panel
friction strip
Figure 29 Friction strip which fits in the channel in the centreboard box
choppy waters Unless you are able to achieve high tolerances when manufacturingcentreboard box it is difficult to achieve a tight fit without having the centreboard jamwhen it is rotating It is better to leave some clearance in the centreboard box then packthe centreboard tight with what I call ldquofriction stripsrdquo These are simply strips about5 mm thick which are placed in the rebatted channel (shown in figure 26) after the cen-treboard is in place Initially I used plywood but found it wore out quickly so I endedup using sections from a sail batten built up to the required thickness with layers ofcarbon fibre and shown in figure 29 The strips are screwed down to the deck of theboard Make sure you place an adequate screw plug in the board Make the strips longenough so that they are in contact with the centreboard pivot pin figure 29
19
Chapter 3Mast track fin-box and footstrap plugs
When placing fittings into the board it is important to reinforce the board around thefitting using a higher density foam than the polystyrene core My approach was tobuild up a block of foam around each fitting I used 25 mm polyurethane 5 mm HDFand fibreglass to make sandwich panels that go around each part These panels helpspread the load and increase the top surface area of each part so there is more areafor the deck or hull lamination to adhere to I prepared all these parts before I startedbuilding the actual board This gave me practise in vacuum bagging on a small scale
31 Mast track
The part I had most difficulty getting was the sliding mast track I was quoted $200 fora mistral one-design track or $80 for a RSX track I opted for the RSX the only draw-back is that they donrsquot have as much travel as a traditional raceboard track figure 31Figure 32 shows the mast-track-box made out of high density foam The actual trackis screwed into the channel I used footstrap plugs as the anchor points for the screws
Figure 31 RSX mast track
32 Finbox and Footstrap plugs
I used a standard tuttle finbox You may wish to use a deep one instead but I believeformula style fins (or a fin gt 50 cm) are unnecessary for longboards so a standardshould do Foam sandwich panels are packed around the finbox and footstrap plugsto provide reinforcement figure 33
20
Design and construction of a windsurfer longboard
Figure 32 Mast track box made of urethaneHDFfibre sandwich
Figure 33 Finbox and footstrap plug reinforcements made of urethaneHDFfibresandwich
21
Chapter 4Board Construction
41 Shaping
The board is shaped as much as possible using a hotwire cutter Since the hotwire is astraight wire you cannot shaped doubly curved surfaces with it eg rails and deck forthese areas I shaped with sandpaper The sequence of shaping is as follows
1 hotwire cut rocker
2 hotwire cut vee
3 hotwire cut planshape
4 hotwire cut linear approximation of rail profile
5 hand sand deck and rail to required curve
The idea is to do as much shaping with a hotwire using templates to guide the cutEven when it came to fairing in the deck and rails I used cardboard templates of thecurve
411 Templates
I used A3 paper to print out templates of the centre-line profile (ie rocker) and plan-shape When creating these templates I subtracted the thickness of the HDF foam offthe template outline so that the specifications given earlier are for the built board notthe core To plot the profiles in full scale I used the vector graphics language AsymptoteSince an A3 piece of paper is 594times 420 mm I printed a section of the profile on eachpage then joined them all together These are the pdf files containing the templates
bull core-centre-linepdf
bull planshape-portpdf
bull planshape-starpdf 1
1Note the maximum half-width of the board is wider than an A3 sheet of paper so the planshape inthese files is referenced to a line offset 25 mm from the centre-line
22
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
5 The finished product 3551 Photos from Inverloch 25042010 39
A Tooling 44A1 Compressor 44A2 Vacuum controller 44A3 Hotwire cutter 46A4 Hotwire voltage control 46
B References and links 49
4
Chapter 1Board design
11 Maximum dimensions
maximum length = l = 3800 mmmaximum width = wm = 640 mmmaximum thickness = tm = 180 mm
12 Rocker profile
The bottom rocker profile ρ (in mm) is defined by the equation
ρ(x) =
0 x lt 800
(xminus 800)4
3times 1011 x gt 800(11)
where x (in mm) is the lengthwise coordinate and ρ is measured relative to the hori-zontal datum z = 0 where z is the vertical coordinate as defined in figure 11 Henceat the stern of the board (ie for x lt 800 mm) the rocker is a true flat Forward ofx = 800 mm the rocker is defined by a quartic giving a maximum rocker value at thebow of the board of ρ = 270 mm The quartic curve generates very little rocker initiallyitrsquos only around x = 2000 m that the rocker starts to kick in
Actually the rocker profile given by (11) can be expressed in terms of two inde-pendent parameters the maximum rocker ρm and the coordinate where the rockerbegins x f Rewriting (11) in terms of these two parameters gives
ρ(x) =
0 x lt x f
ρm
(xminus x f
l minus x f
)4
x gt x f(12)
where l is the maximum length
5
Design and construction of a windsurfer longboard
13 Deck centre-line profile
The deck profile was generated by sketching a spline keeping in mind I didnrsquot wantthe trailing edge of the centreboard to protrude through the deck when it was in theretracted position The centreboard has a maximum chord of 170 mm so the maximumthickness of the board was set to 180 mm
14 Vee concaves tail kick
The reference board I used during the design was heavily concaved figure 12 Irsquom notsure how one would accurately shape these contours In any case most modern boardsseem to have abandoned concaves A simple vee should do the job of counteracting theslapping tendency of a flat hull which concaves also serve to do Concaves may assistis lateral resistance but probably add drag there seems to be very little information ontheir effect In the end I decided to go for a small amount of vee only no tail kick orconcaves The actual vee is constant at 1 degree along the full length
15 Planshape
Figure 13 shows the planshape of the bottom of the board The rails are parallel forapproximately the range x = 1700 to x = 2100 mm where the width is the maximumvalue wm = 640 mm The planshape was generated by a spline sketch and hencecannot be represented in equation form although its not far off an ellipse
16 Deck cross section and rails
Finally the deck and rail profiles are required to completely specify the geometry ofthe board Raceboards have sharp rails which run almost the complete length of theboard This feature greatly simplifies the design since one cross sectional profile canbe specified and simply scaled appropriately based on the thickness and width of theboard at a given x coordinate I played around with using quadratics arcs and thelike to define the cross section but in the end it was simpler just to sketch a spline thatlooked about right Figure 14 shows the normalised cross section used for all locationsIrsquoll probably knock the corner off this profile near the nose of the board where sharprails are more of a liability
Individual cross sectional profiles for the back half of the board are shown in fig-ure 15 and for the front half of the board in figure 16 The area bounded by theindividual cross sections can be calculated by numerically integrating the curves andhence the volume of the board is calculated from the summation
V = A1∆x1 + A2∆x2 + A3∆x3 + + An∆xn =n
sumi
Ai∆xi
where Ai is the area of the ith cross section and ∆xi is the ldquothicknessrdquo of the crosssection slice For the data given above the volume turns out to be
V = 252 litres
6
Design and construction of a windsurfer longboard
The surface area of the board can be found by calculating the length of individuallines show in figures 15 and 16 For the deck and rails this length is given by integrat-ing the upper curves using the formula
S =int w2
minusw2
radic1 +
(dzdy
)2
dy
If this is done for many x locations on the board then the surface area is given by thesummation
A =n
sumi
Si∆xi = 256 m2 deck and rails
A similar calculation can by done for the bottom of the board but it is much simplersince the lines are straight and at a given x location
S =w
cos θ
where θ is the vee angle which is small and hence S asymp w so
A =int 3800
0w dx = 195 m2 bottom
where w is the width of the board which is a function of x
17 Data files
Plain text files containing the coordinates for the
Figure 12 The board used as a rough guide for the design The actual board I designedis quite different the only dimension I matched was the maximum rocker (nose kick)Itrsquos good to have something to reference your design against just to ensure you donrsquotdesign something ldquooff the scalerdquo
9
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
x (mm)
0
y (mm)
l = 3800mm
w
Stern
500 1000 1500 2000 2500 3000 3500-500
0
500
170 320 1375 2180
1580535
Figure 13 Planshape
10
Design and construction of a windsurfer longboard
yw2
zt
05
0-1 -05 0 05 1
1
Figure 14 Spline defining the deck and rail normalised curve
x=100
x=250
x=500
x=750
x=1000
x=1500
x=1900
x=750
x=1000
x=1500
x=1900
z 100
150
200
50
0-350 -250 -150 -50 y 50 150 250 350
Figure 15 Individual cross sectional profiles for the back half of the board Noteconstant vee of 1o Note in these figures Irsquom really plotting zminus ρ ie Irsquom not includingthe effect of the rocker which would shift each successive curve upwards as you moveforward along the board
x=2000
x=2500
x=3000
x=3250
x=3500
x=3600
x=3700
x=3750
x=3250
z 100
150
200
50
0-350 -250 -150 -50 y 50 150 250 350
Figure 16 Individual cross sectional profiles for the front half of the board Noteconstant vee of 1o
11
Design and construction of a windsurfer longboard
18 Design weight
Summarising the design volume and total surface area are
Volume = 252 l and Area = 45 m2
The construction will be carbon sandwich with the following layup 200 gmminus2 car-bon fibre then high density foam (HDF) 80 gmminus3 with a thickness of 5 mm then anothercarbon layer (200gmminus2) Epoxy resin will be used and assuming a fibre to resin ratio of40 60 (see FGI data) then each layer of carbon will require 300 gmminus2 of resin Hencean individual carbon lamination will weigh 500 gmminus2 (note FGI quotes 480) The HDFwill add 80times 5times 10minus3 = 400 gmminus2 So HDF sandwiched between two layers of carbonthe skin weight is 45times (2times 500 + 400) gmminus2 which gives a total of
carbon sandwich weight = 63 kg
The core is low density polystyrene with a density of 14 kgmminus3 which gives a
core weight = 0252times 14 = 35 kg
and hence the subtotal of board without fittings and paint is 98 kgThe other components are estimated to weigh
bull centreboard case 12 kg (HDF carbon construction)
bull Mast track 11 kg (055 kg RSX part +055 kg for reinforcements)
bull Fin Box 06 kg (Tuttle std and reinforcements)
bull Footstrap plugs (times12) 04 kg
bull Fibre patches around fitting 05 kg (1 m2)
So total weight of fittings is 38 kg1 For filling and painting the estimates are
Filler =02 kgPaint =05 kg maximum estimate assuming 1 litres of paint
Hencetotal weight = 143 kg
excluding centreboard (which weighs 085 kg) footstraps amp finNote an additional full lamination adds 10Y g where Y is the fibre weight is gmminus2
ie 130 gmminus2 glass fibre adds a further 13 kg For comparison the claimed weightsof currently available production boards are Starboard Phantom 139 kg Exocet Warp135 kg and Mistral One Design 155 kg
1will lose about 35 kg when polystyrene is routed out
Table 12 lists the actual costs of the materials that go into the board If you where tobuild in glass only you could probably get it down to $1300 There is excess HDF but2 sheets isnrsquot quite enough There is also the cost of consumables
bull paint brushes rollers
bull sandpaper
bull masking tape
bull gloves masks
bull material for templates
bull measuring beakers
I didnrsquot keep track of the cost of the consumables but itrsquos of the order $100 The othercosts include footstraps which for a the full 8 straps at $25 each would be $200 (luckilyI had some old ones I could use) and a fin $150 One thing I hadnrsquot factored in was theuniextension I tried to adapt an existing uni by replacing the pin to suit the rsx trackbut it seems the pin is unique to the rsx track so I could not source a suitable pin Inthe end I had to buy a new rsx mastfoot which was incompatible with my extensionstherefore a new extension too all up another $120
I have not included the cost of any tools I had to buy eg sur-form set-square andany of the electronics associated with the vacuum pump and hotwire
Table 12 Actual material costs in Australian dollars August 2008 For comparisonExocet Warp 380 raceboard $3500 Starboard formula $3150 Starboard Futura (freerideboard) $2500 or Neil Pryde X9 - 490cm mast $1600 For the complete board also factorin footstraps and fin and possibly the unimast extension These items take the costto around $2000 which is more than a Exocet Kona My point is you have to have acompelling reason to build it yourself other than cost
110 Time required to build
This was the most challenging aspect and I would advise anyone thinking of buildingto realistically consider whether they have the time available to complete the projectFor me the project changed from being enjoyable to a chore at about the 75 completemark When this happens you tend to start rushing and trying to take short cuts
I made the first hotwire cut on 29 September and applied the last coat of paint on8 November Prior to starting the board Irsquod made the centre board centre board boxmast track box and finbox reinforcement I worked on these bits and pieces over about6 months on and off Also factor in the time to make the templates The following isroughly how much time was spent on each step I estimate at least 100 hours of labourmaybe closer to 200 hours
Job When DaysBuilding the centreboard Sporadically 2-3 weekendsfittings amp templatesHotwire cutting and board shaping Weekend 2 full daysLaminating 80 done Week off work amp weekend 7 full daysFinal deck top lamination Weekend 1 full dayFilling the weave and sanding Weekend 2 part daysMore surface prep Week nights 1 day equivalentPainting amp fitting gaskets melb cup 4 day long weekend couple hrsdayMore painting Before and after work 1 day equivalentFinish painting Weekend 1 full day
14
Chapter 2Centreboard
21 Design of centreboard
The physics of the flow around an aerofoil is not trivial Motivated by the desire forefficient and fast flight a great deal of scientific and engineering research has beendevoted to the problem Methods for predicting the performance of aerofoils involveapproximations which are quite accurate at low angles of attack more challenging ispredicting the stall characteristics
In designing the centreboard there are two main aspects to consider
1 the aerofoil section which includes the maximum thickness of the aerofoil andpoint of maximum thickness
2 the plan shape
Since the centreboard is a symmetric aerofoil camber and twist are zero and the para-metric design space is somewhat reduced A considerable effort can be devoted to thedesign process However it is worth keeping in mind that hand shaping techniqueswill ultimately limit your ability to accurate produce it
211 Aerofoil section
Based on wind tunnel experiments a large database of aerofoil characteristics was com-plied in the 1930rsquos by NACA (National Advisory Committee of Aeronautics nowNASA) Figure 21 shows the what is referred to as the NACA0010 aerofoil sectionThe important parameter is the maximum thickness of this aerofoil which in this caseis 10 of the chord length c (hence the 10 in NACA0010 00 means no camber) Notethe chord is the straight line joining the leading edge to the trailing edge The numbersin figure 21 refer to selected x y (mm) coordinates on the upper surface relative to theorigin at the leading edge where in this example the chord c = 170 mm which is thechord length at the root of the aerofoil (ie at the point where the centreboard is againstthe hull) Left of the vertical red line is where I used the balsa wood moulding whichjust happened to fit the NACA0010 profile quite well The maximum thickness of theaerofoil is at x = 51 mm where y = t2 = 85 and hence t = 17 mm (ie 10 of c)where t is the thickness
Figure 21 The NACA0010 aerofoil section plotted for a chord length of 170 mm Thisfigure is to scale and can be used as a template if you print the page at 100 scale
Figure 22 Contour plot of what we want to achieve with hand tools and limited skillthis is a challenge
As will be seen in the next section we will choose an elliptic planform so that thechord length progressively reduces towards the tip of the centreboard This meanswe must continuously scale down the profile in figure 21 Figure 22 shows the sur-face contour of the centreboard required to achieve a NACA0010 section at all crosssections
212 Planshape
Mathematical analysis of wings is difficult However a classic result obtained in the1930rsquos is that for unswept wings an elliptical planform gives the minimum possibledrag for a given value of lift (ie it achieves the best LiftDrag ratio) So why notuse the elliptical planform if nothing else it looks better than a rectangular shapedcentreboard
22 Construction of centreboard
The centreboard is built using laminated cedar strips wrapped in a layer of carbonglassfibre using epoxy as the resin There are several useful articles on design and construc-tion of centreboard on the Internet (see for example Philrsquos Foils amp Composites MothHardware Phil Stevenson and Design and construction of centreboards and rudders PaulZander )
I used a rough-sawn cedar weather-board and ripped strips of around 35 mm wideSince I was cutting from a weather-board I could rip pieces of different thickness andbuild up a coarse approximation to the final aerofoil section The strips were gluedwith epoxy For the leading edge I used a piece of balsa around 12 mm wide whichwas pre-shaped into an aerofoil leading edge (try a model aircraft shop)
The centreboard is shaped using an electrical sander with coarse sandpaper I onlymade a template of the root sectional profile So at the end of this stage I had a rectan-
16
Design and construction of a windsurfer longboard
Figure 23 Cedar strips (approx 35 mm wide) and rounded balsa lead leading edge
Figure 24 After laminating a layer of carbonglass
gular planform with a constant sectional profile Next I cut the elliptic planform witha jigsaw The aerofoil section needs to be progressively thinned down towards the tip(ie trying to keep the ratio lc constant to achieve the contour of figure 22) To dothis accurately yoursquod need several sectional profiles for several different locations Inthe end I couldnrsquot be bothered with trying to accurately produce figure 22 and justthinned it out by eye Figure 23 shows the centreboard at this point low spots andimperfects have been filled (pink coloured epoxy filler)
After cutting the required shape of the area that goes through the board itrsquos readyto be laminated I used 200 gmminus2 carbon fibre double thickness from the handle toaround 50 mm below the root I ended up adding an extra layer of glass (130 gmminus2) asI thought Irsquod used too much resin and wanted to soak it up I did it all in one go andwrapped it in a vacuum bag and held it under vacuum overnight while it dried Thevacuum isnrsquot essential but does improve the result A photo of the centreboard afterremoving from the vacuum bag is shown in figure 24 the excess fibre on the trailingedge is easily trimmed off with a knife and sanded smooth donrsquot make it razor shape
23 Centreboard Box
The centreboard is highly loaded when working to windward Therefore it is necessaryto reinforce the board at the location of the centreboard I chose to build what I call acentreboard box which serves the same role as the fin box that is it provides structuralsupport for the lateral loading The difference between a fin box and centreboard boxapart from size is that the centreboard box must also provide a pivot point and asufficient cavity for the centreboard to fit in when in the retracted position The side
17
Design and construction of a windsurfer longboard
walls of the box are made of 25 mm thick polyurethane foam with 2 sheets of HDFlaminate onto the surface (between each layer of foam is 130 gmminus2 glass) To providea pivot point a 5 mm thick piece of marine ply is used with a channel cut into it Thispiece is plywood is recessed into the top HDF layer which also has a channel cut intoit Figure 25 shows the foam and plywood layup and figure 26 shows details of thepivot point prior to the final lamination The final lamination is made up of a layer of200gmminus2 carbon and a layer of 130 gmminus2 glass
180 mm
25 mm urethane foam
5 mm PVC5 mm plywood
1000 mm
Figure 25 Layup of sidewall panels for centreboard box
Figure 26 Plywood reinforcement provides support for centreboard pivot
The width of the centreboard box cavity is asymp 25 mm and chocks of foam 25 mmthick are glued in between the side wall panels At the front of the box I used a trian-gular shaped piece of HDF and at the rear I used polyurethane foam shaped to followthe shape of the trailing edge of the centreboard figure 27These chocks of foam werefirst laminated with fibreglass before gluing them in between the side panels Afterusing the board a few times I discovered a small leak at the rear of the box between thecentral piece of foam and the sidewalls so Irsquod recommend also laying a layer of fibre-glass over the join By sanding or building up the strips you can adjust the amount offriction holding the centreboard
Layers of
HDF foam 25 mmpolyurethane
foam
Figure 27 Foam panels placed in between the sidewall panels
Ideally the centreboard should be a firm fit in the box otherwise when in the re-tracted position it has a tendency to flop back down particularly when bouncing over
18
Design and construction of a windsurfer longboard
Figure 28 Centre board box bottom view
pivot pin of centreboard
Deck
sidewall panel
friction strip
Figure 29 Friction strip which fits in the channel in the centreboard box
choppy waters Unless you are able to achieve high tolerances when manufacturingcentreboard box it is difficult to achieve a tight fit without having the centreboard jamwhen it is rotating It is better to leave some clearance in the centreboard box then packthe centreboard tight with what I call ldquofriction stripsrdquo These are simply strips about5 mm thick which are placed in the rebatted channel (shown in figure 26) after the cen-treboard is in place Initially I used plywood but found it wore out quickly so I endedup using sections from a sail batten built up to the required thickness with layers ofcarbon fibre and shown in figure 29 The strips are screwed down to the deck of theboard Make sure you place an adequate screw plug in the board Make the strips longenough so that they are in contact with the centreboard pivot pin figure 29
19
Chapter 3Mast track fin-box and footstrap plugs
When placing fittings into the board it is important to reinforce the board around thefitting using a higher density foam than the polystyrene core My approach was tobuild up a block of foam around each fitting I used 25 mm polyurethane 5 mm HDFand fibreglass to make sandwich panels that go around each part These panels helpspread the load and increase the top surface area of each part so there is more areafor the deck or hull lamination to adhere to I prepared all these parts before I startedbuilding the actual board This gave me practise in vacuum bagging on a small scale
31 Mast track
The part I had most difficulty getting was the sliding mast track I was quoted $200 fora mistral one-design track or $80 for a RSX track I opted for the RSX the only draw-back is that they donrsquot have as much travel as a traditional raceboard track figure 31Figure 32 shows the mast-track-box made out of high density foam The actual trackis screwed into the channel I used footstrap plugs as the anchor points for the screws
Figure 31 RSX mast track
32 Finbox and Footstrap plugs
I used a standard tuttle finbox You may wish to use a deep one instead but I believeformula style fins (or a fin gt 50 cm) are unnecessary for longboards so a standardshould do Foam sandwich panels are packed around the finbox and footstrap plugsto provide reinforcement figure 33
20
Design and construction of a windsurfer longboard
Figure 32 Mast track box made of urethaneHDFfibre sandwich
Figure 33 Finbox and footstrap plug reinforcements made of urethaneHDFfibresandwich
21
Chapter 4Board Construction
41 Shaping
The board is shaped as much as possible using a hotwire cutter Since the hotwire is astraight wire you cannot shaped doubly curved surfaces with it eg rails and deck forthese areas I shaped with sandpaper The sequence of shaping is as follows
1 hotwire cut rocker
2 hotwire cut vee
3 hotwire cut planshape
4 hotwire cut linear approximation of rail profile
5 hand sand deck and rail to required curve
The idea is to do as much shaping with a hotwire using templates to guide the cutEven when it came to fairing in the deck and rails I used cardboard templates of thecurve
411 Templates
I used A3 paper to print out templates of the centre-line profile (ie rocker) and plan-shape When creating these templates I subtracted the thickness of the HDF foam offthe template outline so that the specifications given earlier are for the built board notthe core To plot the profiles in full scale I used the vector graphics language AsymptoteSince an A3 piece of paper is 594times 420 mm I printed a section of the profile on eachpage then joined them all together These are the pdf files containing the templates
bull core-centre-linepdf
bull planshape-portpdf
bull planshape-starpdf 1
1Note the maximum half-width of the board is wider than an A3 sheet of paper so the planshape inthese files is referenced to a line offset 25 mm from the centre-line
22
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Chapter 1Board design
11 Maximum dimensions
maximum length = l = 3800 mmmaximum width = wm = 640 mmmaximum thickness = tm = 180 mm
12 Rocker profile
The bottom rocker profile ρ (in mm) is defined by the equation
ρ(x) =
0 x lt 800
(xminus 800)4
3times 1011 x gt 800(11)
where x (in mm) is the lengthwise coordinate and ρ is measured relative to the hori-zontal datum z = 0 where z is the vertical coordinate as defined in figure 11 Henceat the stern of the board (ie for x lt 800 mm) the rocker is a true flat Forward ofx = 800 mm the rocker is defined by a quartic giving a maximum rocker value at thebow of the board of ρ = 270 mm The quartic curve generates very little rocker initiallyitrsquos only around x = 2000 m that the rocker starts to kick in
Actually the rocker profile given by (11) can be expressed in terms of two inde-pendent parameters the maximum rocker ρm and the coordinate where the rockerbegins x f Rewriting (11) in terms of these two parameters gives
ρ(x) =
0 x lt x f
ρm
(xminus x f
l minus x f
)4
x gt x f(12)
where l is the maximum length
5
Design and construction of a windsurfer longboard
13 Deck centre-line profile
The deck profile was generated by sketching a spline keeping in mind I didnrsquot wantthe trailing edge of the centreboard to protrude through the deck when it was in theretracted position The centreboard has a maximum chord of 170 mm so the maximumthickness of the board was set to 180 mm
14 Vee concaves tail kick
The reference board I used during the design was heavily concaved figure 12 Irsquom notsure how one would accurately shape these contours In any case most modern boardsseem to have abandoned concaves A simple vee should do the job of counteracting theslapping tendency of a flat hull which concaves also serve to do Concaves may assistis lateral resistance but probably add drag there seems to be very little information ontheir effect In the end I decided to go for a small amount of vee only no tail kick orconcaves The actual vee is constant at 1 degree along the full length
15 Planshape
Figure 13 shows the planshape of the bottom of the board The rails are parallel forapproximately the range x = 1700 to x = 2100 mm where the width is the maximumvalue wm = 640 mm The planshape was generated by a spline sketch and hencecannot be represented in equation form although its not far off an ellipse
16 Deck cross section and rails
Finally the deck and rail profiles are required to completely specify the geometry ofthe board Raceboards have sharp rails which run almost the complete length of theboard This feature greatly simplifies the design since one cross sectional profile canbe specified and simply scaled appropriately based on the thickness and width of theboard at a given x coordinate I played around with using quadratics arcs and thelike to define the cross section but in the end it was simpler just to sketch a spline thatlooked about right Figure 14 shows the normalised cross section used for all locationsIrsquoll probably knock the corner off this profile near the nose of the board where sharprails are more of a liability
Individual cross sectional profiles for the back half of the board are shown in fig-ure 15 and for the front half of the board in figure 16 The area bounded by theindividual cross sections can be calculated by numerically integrating the curves andhence the volume of the board is calculated from the summation
V = A1∆x1 + A2∆x2 + A3∆x3 + + An∆xn =n
sumi
Ai∆xi
where Ai is the area of the ith cross section and ∆xi is the ldquothicknessrdquo of the crosssection slice For the data given above the volume turns out to be
V = 252 litres
6
Design and construction of a windsurfer longboard
The surface area of the board can be found by calculating the length of individuallines show in figures 15 and 16 For the deck and rails this length is given by integrat-ing the upper curves using the formula
S =int w2
minusw2
radic1 +
(dzdy
)2
dy
If this is done for many x locations on the board then the surface area is given by thesummation
A =n
sumi
Si∆xi = 256 m2 deck and rails
A similar calculation can by done for the bottom of the board but it is much simplersince the lines are straight and at a given x location
S =w
cos θ
where θ is the vee angle which is small and hence S asymp w so
A =int 3800
0w dx = 195 m2 bottom
where w is the width of the board which is a function of x
17 Data files
Plain text files containing the coordinates for the
Figure 12 The board used as a rough guide for the design The actual board I designedis quite different the only dimension I matched was the maximum rocker (nose kick)Itrsquos good to have something to reference your design against just to ensure you donrsquotdesign something ldquooff the scalerdquo
9
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
x (mm)
0
y (mm)
l = 3800mm
w
Stern
500 1000 1500 2000 2500 3000 3500-500
0
500
170 320 1375 2180
1580535
Figure 13 Planshape
10
Design and construction of a windsurfer longboard
yw2
zt
05
0-1 -05 0 05 1
1
Figure 14 Spline defining the deck and rail normalised curve
x=100
x=250
x=500
x=750
x=1000
x=1500
x=1900
x=750
x=1000
x=1500
x=1900
z 100
150
200
50
0-350 -250 -150 -50 y 50 150 250 350
Figure 15 Individual cross sectional profiles for the back half of the board Noteconstant vee of 1o Note in these figures Irsquom really plotting zminus ρ ie Irsquom not includingthe effect of the rocker which would shift each successive curve upwards as you moveforward along the board
x=2000
x=2500
x=3000
x=3250
x=3500
x=3600
x=3700
x=3750
x=3250
z 100
150
200
50
0-350 -250 -150 -50 y 50 150 250 350
Figure 16 Individual cross sectional profiles for the front half of the board Noteconstant vee of 1o
11
Design and construction of a windsurfer longboard
18 Design weight
Summarising the design volume and total surface area are
Volume = 252 l and Area = 45 m2
The construction will be carbon sandwich with the following layup 200 gmminus2 car-bon fibre then high density foam (HDF) 80 gmminus3 with a thickness of 5 mm then anothercarbon layer (200gmminus2) Epoxy resin will be used and assuming a fibre to resin ratio of40 60 (see FGI data) then each layer of carbon will require 300 gmminus2 of resin Hencean individual carbon lamination will weigh 500 gmminus2 (note FGI quotes 480) The HDFwill add 80times 5times 10minus3 = 400 gmminus2 So HDF sandwiched between two layers of carbonthe skin weight is 45times (2times 500 + 400) gmminus2 which gives a total of
carbon sandwich weight = 63 kg
The core is low density polystyrene with a density of 14 kgmminus3 which gives a
core weight = 0252times 14 = 35 kg
and hence the subtotal of board without fittings and paint is 98 kgThe other components are estimated to weigh
bull centreboard case 12 kg (HDF carbon construction)
bull Mast track 11 kg (055 kg RSX part +055 kg for reinforcements)
bull Fin Box 06 kg (Tuttle std and reinforcements)
bull Footstrap plugs (times12) 04 kg
bull Fibre patches around fitting 05 kg (1 m2)
So total weight of fittings is 38 kg1 For filling and painting the estimates are
Filler =02 kgPaint =05 kg maximum estimate assuming 1 litres of paint
Hencetotal weight = 143 kg
excluding centreboard (which weighs 085 kg) footstraps amp finNote an additional full lamination adds 10Y g where Y is the fibre weight is gmminus2
ie 130 gmminus2 glass fibre adds a further 13 kg For comparison the claimed weightsof currently available production boards are Starboard Phantom 139 kg Exocet Warp135 kg and Mistral One Design 155 kg
1will lose about 35 kg when polystyrene is routed out
Table 12 lists the actual costs of the materials that go into the board If you where tobuild in glass only you could probably get it down to $1300 There is excess HDF but2 sheets isnrsquot quite enough There is also the cost of consumables
bull paint brushes rollers
bull sandpaper
bull masking tape
bull gloves masks
bull material for templates
bull measuring beakers
I didnrsquot keep track of the cost of the consumables but itrsquos of the order $100 The othercosts include footstraps which for a the full 8 straps at $25 each would be $200 (luckilyI had some old ones I could use) and a fin $150 One thing I hadnrsquot factored in was theuniextension I tried to adapt an existing uni by replacing the pin to suit the rsx trackbut it seems the pin is unique to the rsx track so I could not source a suitable pin Inthe end I had to buy a new rsx mastfoot which was incompatible with my extensionstherefore a new extension too all up another $120
I have not included the cost of any tools I had to buy eg sur-form set-square andany of the electronics associated with the vacuum pump and hotwire
Table 12 Actual material costs in Australian dollars August 2008 For comparisonExocet Warp 380 raceboard $3500 Starboard formula $3150 Starboard Futura (freerideboard) $2500 or Neil Pryde X9 - 490cm mast $1600 For the complete board also factorin footstraps and fin and possibly the unimast extension These items take the costto around $2000 which is more than a Exocet Kona My point is you have to have acompelling reason to build it yourself other than cost
110 Time required to build
This was the most challenging aspect and I would advise anyone thinking of buildingto realistically consider whether they have the time available to complete the projectFor me the project changed from being enjoyable to a chore at about the 75 completemark When this happens you tend to start rushing and trying to take short cuts
I made the first hotwire cut on 29 September and applied the last coat of paint on8 November Prior to starting the board Irsquod made the centre board centre board boxmast track box and finbox reinforcement I worked on these bits and pieces over about6 months on and off Also factor in the time to make the templates The following isroughly how much time was spent on each step I estimate at least 100 hours of labourmaybe closer to 200 hours
Job When DaysBuilding the centreboard Sporadically 2-3 weekendsfittings amp templatesHotwire cutting and board shaping Weekend 2 full daysLaminating 80 done Week off work amp weekend 7 full daysFinal deck top lamination Weekend 1 full dayFilling the weave and sanding Weekend 2 part daysMore surface prep Week nights 1 day equivalentPainting amp fitting gaskets melb cup 4 day long weekend couple hrsdayMore painting Before and after work 1 day equivalentFinish painting Weekend 1 full day
14
Chapter 2Centreboard
21 Design of centreboard
The physics of the flow around an aerofoil is not trivial Motivated by the desire forefficient and fast flight a great deal of scientific and engineering research has beendevoted to the problem Methods for predicting the performance of aerofoils involveapproximations which are quite accurate at low angles of attack more challenging ispredicting the stall characteristics
In designing the centreboard there are two main aspects to consider
1 the aerofoil section which includes the maximum thickness of the aerofoil andpoint of maximum thickness
2 the plan shape
Since the centreboard is a symmetric aerofoil camber and twist are zero and the para-metric design space is somewhat reduced A considerable effort can be devoted to thedesign process However it is worth keeping in mind that hand shaping techniqueswill ultimately limit your ability to accurate produce it
211 Aerofoil section
Based on wind tunnel experiments a large database of aerofoil characteristics was com-plied in the 1930rsquos by NACA (National Advisory Committee of Aeronautics nowNASA) Figure 21 shows the what is referred to as the NACA0010 aerofoil sectionThe important parameter is the maximum thickness of this aerofoil which in this caseis 10 of the chord length c (hence the 10 in NACA0010 00 means no camber) Notethe chord is the straight line joining the leading edge to the trailing edge The numbersin figure 21 refer to selected x y (mm) coordinates on the upper surface relative to theorigin at the leading edge where in this example the chord c = 170 mm which is thechord length at the root of the aerofoil (ie at the point where the centreboard is againstthe hull) Left of the vertical red line is where I used the balsa wood moulding whichjust happened to fit the NACA0010 profile quite well The maximum thickness of theaerofoil is at x = 51 mm where y = t2 = 85 and hence t = 17 mm (ie 10 of c)where t is the thickness
Figure 21 The NACA0010 aerofoil section plotted for a chord length of 170 mm Thisfigure is to scale and can be used as a template if you print the page at 100 scale
Figure 22 Contour plot of what we want to achieve with hand tools and limited skillthis is a challenge
As will be seen in the next section we will choose an elliptic planform so that thechord length progressively reduces towards the tip of the centreboard This meanswe must continuously scale down the profile in figure 21 Figure 22 shows the sur-face contour of the centreboard required to achieve a NACA0010 section at all crosssections
212 Planshape
Mathematical analysis of wings is difficult However a classic result obtained in the1930rsquos is that for unswept wings an elliptical planform gives the minimum possibledrag for a given value of lift (ie it achieves the best LiftDrag ratio) So why notuse the elliptical planform if nothing else it looks better than a rectangular shapedcentreboard
22 Construction of centreboard
The centreboard is built using laminated cedar strips wrapped in a layer of carbonglassfibre using epoxy as the resin There are several useful articles on design and construc-tion of centreboard on the Internet (see for example Philrsquos Foils amp Composites MothHardware Phil Stevenson and Design and construction of centreboards and rudders PaulZander )
I used a rough-sawn cedar weather-board and ripped strips of around 35 mm wideSince I was cutting from a weather-board I could rip pieces of different thickness andbuild up a coarse approximation to the final aerofoil section The strips were gluedwith epoxy For the leading edge I used a piece of balsa around 12 mm wide whichwas pre-shaped into an aerofoil leading edge (try a model aircraft shop)
The centreboard is shaped using an electrical sander with coarse sandpaper I onlymade a template of the root sectional profile So at the end of this stage I had a rectan-
16
Design and construction of a windsurfer longboard
Figure 23 Cedar strips (approx 35 mm wide) and rounded balsa lead leading edge
Figure 24 After laminating a layer of carbonglass
gular planform with a constant sectional profile Next I cut the elliptic planform witha jigsaw The aerofoil section needs to be progressively thinned down towards the tip(ie trying to keep the ratio lc constant to achieve the contour of figure 22) To dothis accurately yoursquod need several sectional profiles for several different locations Inthe end I couldnrsquot be bothered with trying to accurately produce figure 22 and justthinned it out by eye Figure 23 shows the centreboard at this point low spots andimperfects have been filled (pink coloured epoxy filler)
After cutting the required shape of the area that goes through the board itrsquos readyto be laminated I used 200 gmminus2 carbon fibre double thickness from the handle toaround 50 mm below the root I ended up adding an extra layer of glass (130 gmminus2) asI thought Irsquod used too much resin and wanted to soak it up I did it all in one go andwrapped it in a vacuum bag and held it under vacuum overnight while it dried Thevacuum isnrsquot essential but does improve the result A photo of the centreboard afterremoving from the vacuum bag is shown in figure 24 the excess fibre on the trailingedge is easily trimmed off with a knife and sanded smooth donrsquot make it razor shape
23 Centreboard Box
The centreboard is highly loaded when working to windward Therefore it is necessaryto reinforce the board at the location of the centreboard I chose to build what I call acentreboard box which serves the same role as the fin box that is it provides structuralsupport for the lateral loading The difference between a fin box and centreboard boxapart from size is that the centreboard box must also provide a pivot point and asufficient cavity for the centreboard to fit in when in the retracted position The side
17
Design and construction of a windsurfer longboard
walls of the box are made of 25 mm thick polyurethane foam with 2 sheets of HDFlaminate onto the surface (between each layer of foam is 130 gmminus2 glass) To providea pivot point a 5 mm thick piece of marine ply is used with a channel cut into it Thispiece is plywood is recessed into the top HDF layer which also has a channel cut intoit Figure 25 shows the foam and plywood layup and figure 26 shows details of thepivot point prior to the final lamination The final lamination is made up of a layer of200gmminus2 carbon and a layer of 130 gmminus2 glass
180 mm
25 mm urethane foam
5 mm PVC5 mm plywood
1000 mm
Figure 25 Layup of sidewall panels for centreboard box
Figure 26 Plywood reinforcement provides support for centreboard pivot
The width of the centreboard box cavity is asymp 25 mm and chocks of foam 25 mmthick are glued in between the side wall panels At the front of the box I used a trian-gular shaped piece of HDF and at the rear I used polyurethane foam shaped to followthe shape of the trailing edge of the centreboard figure 27These chocks of foam werefirst laminated with fibreglass before gluing them in between the side panels Afterusing the board a few times I discovered a small leak at the rear of the box between thecentral piece of foam and the sidewalls so Irsquod recommend also laying a layer of fibre-glass over the join By sanding or building up the strips you can adjust the amount offriction holding the centreboard
Layers of
HDF foam 25 mmpolyurethane
foam
Figure 27 Foam panels placed in between the sidewall panels
Ideally the centreboard should be a firm fit in the box otherwise when in the re-tracted position it has a tendency to flop back down particularly when bouncing over
18
Design and construction of a windsurfer longboard
Figure 28 Centre board box bottom view
pivot pin of centreboard
Deck
sidewall panel
friction strip
Figure 29 Friction strip which fits in the channel in the centreboard box
choppy waters Unless you are able to achieve high tolerances when manufacturingcentreboard box it is difficult to achieve a tight fit without having the centreboard jamwhen it is rotating It is better to leave some clearance in the centreboard box then packthe centreboard tight with what I call ldquofriction stripsrdquo These are simply strips about5 mm thick which are placed in the rebatted channel (shown in figure 26) after the cen-treboard is in place Initially I used plywood but found it wore out quickly so I endedup using sections from a sail batten built up to the required thickness with layers ofcarbon fibre and shown in figure 29 The strips are screwed down to the deck of theboard Make sure you place an adequate screw plug in the board Make the strips longenough so that they are in contact with the centreboard pivot pin figure 29
19
Chapter 3Mast track fin-box and footstrap plugs
When placing fittings into the board it is important to reinforce the board around thefitting using a higher density foam than the polystyrene core My approach was tobuild up a block of foam around each fitting I used 25 mm polyurethane 5 mm HDFand fibreglass to make sandwich panels that go around each part These panels helpspread the load and increase the top surface area of each part so there is more areafor the deck or hull lamination to adhere to I prepared all these parts before I startedbuilding the actual board This gave me practise in vacuum bagging on a small scale
31 Mast track
The part I had most difficulty getting was the sliding mast track I was quoted $200 fora mistral one-design track or $80 for a RSX track I opted for the RSX the only draw-back is that they donrsquot have as much travel as a traditional raceboard track figure 31Figure 32 shows the mast-track-box made out of high density foam The actual trackis screwed into the channel I used footstrap plugs as the anchor points for the screws
Figure 31 RSX mast track
32 Finbox and Footstrap plugs
I used a standard tuttle finbox You may wish to use a deep one instead but I believeformula style fins (or a fin gt 50 cm) are unnecessary for longboards so a standardshould do Foam sandwich panels are packed around the finbox and footstrap plugsto provide reinforcement figure 33
20
Design and construction of a windsurfer longboard
Figure 32 Mast track box made of urethaneHDFfibre sandwich
Figure 33 Finbox and footstrap plug reinforcements made of urethaneHDFfibresandwich
21
Chapter 4Board Construction
41 Shaping
The board is shaped as much as possible using a hotwire cutter Since the hotwire is astraight wire you cannot shaped doubly curved surfaces with it eg rails and deck forthese areas I shaped with sandpaper The sequence of shaping is as follows
1 hotwire cut rocker
2 hotwire cut vee
3 hotwire cut planshape
4 hotwire cut linear approximation of rail profile
5 hand sand deck and rail to required curve
The idea is to do as much shaping with a hotwire using templates to guide the cutEven when it came to fairing in the deck and rails I used cardboard templates of thecurve
411 Templates
I used A3 paper to print out templates of the centre-line profile (ie rocker) and plan-shape When creating these templates I subtracted the thickness of the HDF foam offthe template outline so that the specifications given earlier are for the built board notthe core To plot the profiles in full scale I used the vector graphics language AsymptoteSince an A3 piece of paper is 594times 420 mm I printed a section of the profile on eachpage then joined them all together These are the pdf files containing the templates
bull core-centre-linepdf
bull planshape-portpdf
bull planshape-starpdf 1
1Note the maximum half-width of the board is wider than an A3 sheet of paper so the planshape inthese files is referenced to a line offset 25 mm from the centre-line
22
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
13 Deck centre-line profile
The deck profile was generated by sketching a spline keeping in mind I didnrsquot wantthe trailing edge of the centreboard to protrude through the deck when it was in theretracted position The centreboard has a maximum chord of 170 mm so the maximumthickness of the board was set to 180 mm
14 Vee concaves tail kick
The reference board I used during the design was heavily concaved figure 12 Irsquom notsure how one would accurately shape these contours In any case most modern boardsseem to have abandoned concaves A simple vee should do the job of counteracting theslapping tendency of a flat hull which concaves also serve to do Concaves may assistis lateral resistance but probably add drag there seems to be very little information ontheir effect In the end I decided to go for a small amount of vee only no tail kick orconcaves The actual vee is constant at 1 degree along the full length
15 Planshape
Figure 13 shows the planshape of the bottom of the board The rails are parallel forapproximately the range x = 1700 to x = 2100 mm where the width is the maximumvalue wm = 640 mm The planshape was generated by a spline sketch and hencecannot be represented in equation form although its not far off an ellipse
16 Deck cross section and rails
Finally the deck and rail profiles are required to completely specify the geometry ofthe board Raceboards have sharp rails which run almost the complete length of theboard This feature greatly simplifies the design since one cross sectional profile canbe specified and simply scaled appropriately based on the thickness and width of theboard at a given x coordinate I played around with using quadratics arcs and thelike to define the cross section but in the end it was simpler just to sketch a spline thatlooked about right Figure 14 shows the normalised cross section used for all locationsIrsquoll probably knock the corner off this profile near the nose of the board where sharprails are more of a liability
Individual cross sectional profiles for the back half of the board are shown in fig-ure 15 and for the front half of the board in figure 16 The area bounded by theindividual cross sections can be calculated by numerically integrating the curves andhence the volume of the board is calculated from the summation
V = A1∆x1 + A2∆x2 + A3∆x3 + + An∆xn =n
sumi
Ai∆xi
where Ai is the area of the ith cross section and ∆xi is the ldquothicknessrdquo of the crosssection slice For the data given above the volume turns out to be
V = 252 litres
6
Design and construction of a windsurfer longboard
The surface area of the board can be found by calculating the length of individuallines show in figures 15 and 16 For the deck and rails this length is given by integrat-ing the upper curves using the formula
S =int w2
minusw2
radic1 +
(dzdy
)2
dy
If this is done for many x locations on the board then the surface area is given by thesummation
A =n
sumi
Si∆xi = 256 m2 deck and rails
A similar calculation can by done for the bottom of the board but it is much simplersince the lines are straight and at a given x location
S =w
cos θ
where θ is the vee angle which is small and hence S asymp w so
A =int 3800
0w dx = 195 m2 bottom
where w is the width of the board which is a function of x
17 Data files
Plain text files containing the coordinates for the
Figure 12 The board used as a rough guide for the design The actual board I designedis quite different the only dimension I matched was the maximum rocker (nose kick)Itrsquos good to have something to reference your design against just to ensure you donrsquotdesign something ldquooff the scalerdquo
9
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
x (mm)
0
y (mm)
l = 3800mm
w
Stern
500 1000 1500 2000 2500 3000 3500-500
0
500
170 320 1375 2180
1580535
Figure 13 Planshape
10
Design and construction of a windsurfer longboard
yw2
zt
05
0-1 -05 0 05 1
1
Figure 14 Spline defining the deck and rail normalised curve
x=100
x=250
x=500
x=750
x=1000
x=1500
x=1900
x=750
x=1000
x=1500
x=1900
z 100
150
200
50
0-350 -250 -150 -50 y 50 150 250 350
Figure 15 Individual cross sectional profiles for the back half of the board Noteconstant vee of 1o Note in these figures Irsquom really plotting zminus ρ ie Irsquom not includingthe effect of the rocker which would shift each successive curve upwards as you moveforward along the board
x=2000
x=2500
x=3000
x=3250
x=3500
x=3600
x=3700
x=3750
x=3250
z 100
150
200
50
0-350 -250 -150 -50 y 50 150 250 350
Figure 16 Individual cross sectional profiles for the front half of the board Noteconstant vee of 1o
11
Design and construction of a windsurfer longboard
18 Design weight
Summarising the design volume and total surface area are
Volume = 252 l and Area = 45 m2
The construction will be carbon sandwich with the following layup 200 gmminus2 car-bon fibre then high density foam (HDF) 80 gmminus3 with a thickness of 5 mm then anothercarbon layer (200gmminus2) Epoxy resin will be used and assuming a fibre to resin ratio of40 60 (see FGI data) then each layer of carbon will require 300 gmminus2 of resin Hencean individual carbon lamination will weigh 500 gmminus2 (note FGI quotes 480) The HDFwill add 80times 5times 10minus3 = 400 gmminus2 So HDF sandwiched between two layers of carbonthe skin weight is 45times (2times 500 + 400) gmminus2 which gives a total of
carbon sandwich weight = 63 kg
The core is low density polystyrene with a density of 14 kgmminus3 which gives a
core weight = 0252times 14 = 35 kg
and hence the subtotal of board without fittings and paint is 98 kgThe other components are estimated to weigh
bull centreboard case 12 kg (HDF carbon construction)
bull Mast track 11 kg (055 kg RSX part +055 kg for reinforcements)
bull Fin Box 06 kg (Tuttle std and reinforcements)
bull Footstrap plugs (times12) 04 kg
bull Fibre patches around fitting 05 kg (1 m2)
So total weight of fittings is 38 kg1 For filling and painting the estimates are
Filler =02 kgPaint =05 kg maximum estimate assuming 1 litres of paint
Hencetotal weight = 143 kg
excluding centreboard (which weighs 085 kg) footstraps amp finNote an additional full lamination adds 10Y g where Y is the fibre weight is gmminus2
ie 130 gmminus2 glass fibre adds a further 13 kg For comparison the claimed weightsof currently available production boards are Starboard Phantom 139 kg Exocet Warp135 kg and Mistral One Design 155 kg
1will lose about 35 kg when polystyrene is routed out
Table 12 lists the actual costs of the materials that go into the board If you where tobuild in glass only you could probably get it down to $1300 There is excess HDF but2 sheets isnrsquot quite enough There is also the cost of consumables
bull paint brushes rollers
bull sandpaper
bull masking tape
bull gloves masks
bull material for templates
bull measuring beakers
I didnrsquot keep track of the cost of the consumables but itrsquos of the order $100 The othercosts include footstraps which for a the full 8 straps at $25 each would be $200 (luckilyI had some old ones I could use) and a fin $150 One thing I hadnrsquot factored in was theuniextension I tried to adapt an existing uni by replacing the pin to suit the rsx trackbut it seems the pin is unique to the rsx track so I could not source a suitable pin Inthe end I had to buy a new rsx mastfoot which was incompatible with my extensionstherefore a new extension too all up another $120
I have not included the cost of any tools I had to buy eg sur-form set-square andany of the electronics associated with the vacuum pump and hotwire
Table 12 Actual material costs in Australian dollars August 2008 For comparisonExocet Warp 380 raceboard $3500 Starboard formula $3150 Starboard Futura (freerideboard) $2500 or Neil Pryde X9 - 490cm mast $1600 For the complete board also factorin footstraps and fin and possibly the unimast extension These items take the costto around $2000 which is more than a Exocet Kona My point is you have to have acompelling reason to build it yourself other than cost
110 Time required to build
This was the most challenging aspect and I would advise anyone thinking of buildingto realistically consider whether they have the time available to complete the projectFor me the project changed from being enjoyable to a chore at about the 75 completemark When this happens you tend to start rushing and trying to take short cuts
I made the first hotwire cut on 29 September and applied the last coat of paint on8 November Prior to starting the board Irsquod made the centre board centre board boxmast track box and finbox reinforcement I worked on these bits and pieces over about6 months on and off Also factor in the time to make the templates The following isroughly how much time was spent on each step I estimate at least 100 hours of labourmaybe closer to 200 hours
Job When DaysBuilding the centreboard Sporadically 2-3 weekendsfittings amp templatesHotwire cutting and board shaping Weekend 2 full daysLaminating 80 done Week off work amp weekend 7 full daysFinal deck top lamination Weekend 1 full dayFilling the weave and sanding Weekend 2 part daysMore surface prep Week nights 1 day equivalentPainting amp fitting gaskets melb cup 4 day long weekend couple hrsdayMore painting Before and after work 1 day equivalentFinish painting Weekend 1 full day
14
Chapter 2Centreboard
21 Design of centreboard
The physics of the flow around an aerofoil is not trivial Motivated by the desire forefficient and fast flight a great deal of scientific and engineering research has beendevoted to the problem Methods for predicting the performance of aerofoils involveapproximations which are quite accurate at low angles of attack more challenging ispredicting the stall characteristics
In designing the centreboard there are two main aspects to consider
1 the aerofoil section which includes the maximum thickness of the aerofoil andpoint of maximum thickness
2 the plan shape
Since the centreboard is a symmetric aerofoil camber and twist are zero and the para-metric design space is somewhat reduced A considerable effort can be devoted to thedesign process However it is worth keeping in mind that hand shaping techniqueswill ultimately limit your ability to accurate produce it
211 Aerofoil section
Based on wind tunnel experiments a large database of aerofoil characteristics was com-plied in the 1930rsquos by NACA (National Advisory Committee of Aeronautics nowNASA) Figure 21 shows the what is referred to as the NACA0010 aerofoil sectionThe important parameter is the maximum thickness of this aerofoil which in this caseis 10 of the chord length c (hence the 10 in NACA0010 00 means no camber) Notethe chord is the straight line joining the leading edge to the trailing edge The numbersin figure 21 refer to selected x y (mm) coordinates on the upper surface relative to theorigin at the leading edge where in this example the chord c = 170 mm which is thechord length at the root of the aerofoil (ie at the point where the centreboard is againstthe hull) Left of the vertical red line is where I used the balsa wood moulding whichjust happened to fit the NACA0010 profile quite well The maximum thickness of theaerofoil is at x = 51 mm where y = t2 = 85 and hence t = 17 mm (ie 10 of c)where t is the thickness
Figure 21 The NACA0010 aerofoil section plotted for a chord length of 170 mm Thisfigure is to scale and can be used as a template if you print the page at 100 scale
Figure 22 Contour plot of what we want to achieve with hand tools and limited skillthis is a challenge
As will be seen in the next section we will choose an elliptic planform so that thechord length progressively reduces towards the tip of the centreboard This meanswe must continuously scale down the profile in figure 21 Figure 22 shows the sur-face contour of the centreboard required to achieve a NACA0010 section at all crosssections
212 Planshape
Mathematical analysis of wings is difficult However a classic result obtained in the1930rsquos is that for unswept wings an elliptical planform gives the minimum possibledrag for a given value of lift (ie it achieves the best LiftDrag ratio) So why notuse the elliptical planform if nothing else it looks better than a rectangular shapedcentreboard
22 Construction of centreboard
The centreboard is built using laminated cedar strips wrapped in a layer of carbonglassfibre using epoxy as the resin There are several useful articles on design and construc-tion of centreboard on the Internet (see for example Philrsquos Foils amp Composites MothHardware Phil Stevenson and Design and construction of centreboards and rudders PaulZander )
I used a rough-sawn cedar weather-board and ripped strips of around 35 mm wideSince I was cutting from a weather-board I could rip pieces of different thickness andbuild up a coarse approximation to the final aerofoil section The strips were gluedwith epoxy For the leading edge I used a piece of balsa around 12 mm wide whichwas pre-shaped into an aerofoil leading edge (try a model aircraft shop)
The centreboard is shaped using an electrical sander with coarse sandpaper I onlymade a template of the root sectional profile So at the end of this stage I had a rectan-
16
Design and construction of a windsurfer longboard
Figure 23 Cedar strips (approx 35 mm wide) and rounded balsa lead leading edge
Figure 24 After laminating a layer of carbonglass
gular planform with a constant sectional profile Next I cut the elliptic planform witha jigsaw The aerofoil section needs to be progressively thinned down towards the tip(ie trying to keep the ratio lc constant to achieve the contour of figure 22) To dothis accurately yoursquod need several sectional profiles for several different locations Inthe end I couldnrsquot be bothered with trying to accurately produce figure 22 and justthinned it out by eye Figure 23 shows the centreboard at this point low spots andimperfects have been filled (pink coloured epoxy filler)
After cutting the required shape of the area that goes through the board itrsquos readyto be laminated I used 200 gmminus2 carbon fibre double thickness from the handle toaround 50 mm below the root I ended up adding an extra layer of glass (130 gmminus2) asI thought Irsquod used too much resin and wanted to soak it up I did it all in one go andwrapped it in a vacuum bag and held it under vacuum overnight while it dried Thevacuum isnrsquot essential but does improve the result A photo of the centreboard afterremoving from the vacuum bag is shown in figure 24 the excess fibre on the trailingedge is easily trimmed off with a knife and sanded smooth donrsquot make it razor shape
23 Centreboard Box
The centreboard is highly loaded when working to windward Therefore it is necessaryto reinforce the board at the location of the centreboard I chose to build what I call acentreboard box which serves the same role as the fin box that is it provides structuralsupport for the lateral loading The difference between a fin box and centreboard boxapart from size is that the centreboard box must also provide a pivot point and asufficient cavity for the centreboard to fit in when in the retracted position The side
17
Design and construction of a windsurfer longboard
walls of the box are made of 25 mm thick polyurethane foam with 2 sheets of HDFlaminate onto the surface (between each layer of foam is 130 gmminus2 glass) To providea pivot point a 5 mm thick piece of marine ply is used with a channel cut into it Thispiece is plywood is recessed into the top HDF layer which also has a channel cut intoit Figure 25 shows the foam and plywood layup and figure 26 shows details of thepivot point prior to the final lamination The final lamination is made up of a layer of200gmminus2 carbon and a layer of 130 gmminus2 glass
180 mm
25 mm urethane foam
5 mm PVC5 mm plywood
1000 mm
Figure 25 Layup of sidewall panels for centreboard box
Figure 26 Plywood reinforcement provides support for centreboard pivot
The width of the centreboard box cavity is asymp 25 mm and chocks of foam 25 mmthick are glued in between the side wall panels At the front of the box I used a trian-gular shaped piece of HDF and at the rear I used polyurethane foam shaped to followthe shape of the trailing edge of the centreboard figure 27These chocks of foam werefirst laminated with fibreglass before gluing them in between the side panels Afterusing the board a few times I discovered a small leak at the rear of the box between thecentral piece of foam and the sidewalls so Irsquod recommend also laying a layer of fibre-glass over the join By sanding or building up the strips you can adjust the amount offriction holding the centreboard
Layers of
HDF foam 25 mmpolyurethane
foam
Figure 27 Foam panels placed in between the sidewall panels
Ideally the centreboard should be a firm fit in the box otherwise when in the re-tracted position it has a tendency to flop back down particularly when bouncing over
18
Design and construction of a windsurfer longboard
Figure 28 Centre board box bottom view
pivot pin of centreboard
Deck
sidewall panel
friction strip
Figure 29 Friction strip which fits in the channel in the centreboard box
choppy waters Unless you are able to achieve high tolerances when manufacturingcentreboard box it is difficult to achieve a tight fit without having the centreboard jamwhen it is rotating It is better to leave some clearance in the centreboard box then packthe centreboard tight with what I call ldquofriction stripsrdquo These are simply strips about5 mm thick which are placed in the rebatted channel (shown in figure 26) after the cen-treboard is in place Initially I used plywood but found it wore out quickly so I endedup using sections from a sail batten built up to the required thickness with layers ofcarbon fibre and shown in figure 29 The strips are screwed down to the deck of theboard Make sure you place an adequate screw plug in the board Make the strips longenough so that they are in contact with the centreboard pivot pin figure 29
19
Chapter 3Mast track fin-box and footstrap plugs
When placing fittings into the board it is important to reinforce the board around thefitting using a higher density foam than the polystyrene core My approach was tobuild up a block of foam around each fitting I used 25 mm polyurethane 5 mm HDFand fibreglass to make sandwich panels that go around each part These panels helpspread the load and increase the top surface area of each part so there is more areafor the deck or hull lamination to adhere to I prepared all these parts before I startedbuilding the actual board This gave me practise in vacuum bagging on a small scale
31 Mast track
The part I had most difficulty getting was the sliding mast track I was quoted $200 fora mistral one-design track or $80 for a RSX track I opted for the RSX the only draw-back is that they donrsquot have as much travel as a traditional raceboard track figure 31Figure 32 shows the mast-track-box made out of high density foam The actual trackis screwed into the channel I used footstrap plugs as the anchor points for the screws
Figure 31 RSX mast track
32 Finbox and Footstrap plugs
I used a standard tuttle finbox You may wish to use a deep one instead but I believeformula style fins (or a fin gt 50 cm) are unnecessary for longboards so a standardshould do Foam sandwich panels are packed around the finbox and footstrap plugsto provide reinforcement figure 33
20
Design and construction of a windsurfer longboard
Figure 32 Mast track box made of urethaneHDFfibre sandwich
Figure 33 Finbox and footstrap plug reinforcements made of urethaneHDFfibresandwich
21
Chapter 4Board Construction
41 Shaping
The board is shaped as much as possible using a hotwire cutter Since the hotwire is astraight wire you cannot shaped doubly curved surfaces with it eg rails and deck forthese areas I shaped with sandpaper The sequence of shaping is as follows
1 hotwire cut rocker
2 hotwire cut vee
3 hotwire cut planshape
4 hotwire cut linear approximation of rail profile
5 hand sand deck and rail to required curve
The idea is to do as much shaping with a hotwire using templates to guide the cutEven when it came to fairing in the deck and rails I used cardboard templates of thecurve
411 Templates
I used A3 paper to print out templates of the centre-line profile (ie rocker) and plan-shape When creating these templates I subtracted the thickness of the HDF foam offthe template outline so that the specifications given earlier are for the built board notthe core To plot the profiles in full scale I used the vector graphics language AsymptoteSince an A3 piece of paper is 594times 420 mm I printed a section of the profile on eachpage then joined them all together These are the pdf files containing the templates
bull core-centre-linepdf
bull planshape-portpdf
bull planshape-starpdf 1
1Note the maximum half-width of the board is wider than an A3 sheet of paper so the planshape inthese files is referenced to a line offset 25 mm from the centre-line
22
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
The surface area of the board can be found by calculating the length of individuallines show in figures 15 and 16 For the deck and rails this length is given by integrat-ing the upper curves using the formula
S =int w2
minusw2
radic1 +
(dzdy
)2
dy
If this is done for many x locations on the board then the surface area is given by thesummation
A =n
sumi
Si∆xi = 256 m2 deck and rails
A similar calculation can by done for the bottom of the board but it is much simplersince the lines are straight and at a given x location
S =w
cos θ
where θ is the vee angle which is small and hence S asymp w so
A =int 3800
0w dx = 195 m2 bottom
where w is the width of the board which is a function of x
17 Data files
Plain text files containing the coordinates for the
Figure 12 The board used as a rough guide for the design The actual board I designedis quite different the only dimension I matched was the maximum rocker (nose kick)Itrsquos good to have something to reference your design against just to ensure you donrsquotdesign something ldquooff the scalerdquo
9
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
x (mm)
0
y (mm)
l = 3800mm
w
Stern
500 1000 1500 2000 2500 3000 3500-500
0
500
170 320 1375 2180
1580535
Figure 13 Planshape
10
Design and construction of a windsurfer longboard
yw2
zt
05
0-1 -05 0 05 1
1
Figure 14 Spline defining the deck and rail normalised curve
x=100
x=250
x=500
x=750
x=1000
x=1500
x=1900
x=750
x=1000
x=1500
x=1900
z 100
150
200
50
0-350 -250 -150 -50 y 50 150 250 350
Figure 15 Individual cross sectional profiles for the back half of the board Noteconstant vee of 1o Note in these figures Irsquom really plotting zminus ρ ie Irsquom not includingthe effect of the rocker which would shift each successive curve upwards as you moveforward along the board
x=2000
x=2500
x=3000
x=3250
x=3500
x=3600
x=3700
x=3750
x=3250
z 100
150
200
50
0-350 -250 -150 -50 y 50 150 250 350
Figure 16 Individual cross sectional profiles for the front half of the board Noteconstant vee of 1o
11
Design and construction of a windsurfer longboard
18 Design weight
Summarising the design volume and total surface area are
Volume = 252 l and Area = 45 m2
The construction will be carbon sandwich with the following layup 200 gmminus2 car-bon fibre then high density foam (HDF) 80 gmminus3 with a thickness of 5 mm then anothercarbon layer (200gmminus2) Epoxy resin will be used and assuming a fibre to resin ratio of40 60 (see FGI data) then each layer of carbon will require 300 gmminus2 of resin Hencean individual carbon lamination will weigh 500 gmminus2 (note FGI quotes 480) The HDFwill add 80times 5times 10minus3 = 400 gmminus2 So HDF sandwiched between two layers of carbonthe skin weight is 45times (2times 500 + 400) gmminus2 which gives a total of
carbon sandwich weight = 63 kg
The core is low density polystyrene with a density of 14 kgmminus3 which gives a
core weight = 0252times 14 = 35 kg
and hence the subtotal of board without fittings and paint is 98 kgThe other components are estimated to weigh
bull centreboard case 12 kg (HDF carbon construction)
bull Mast track 11 kg (055 kg RSX part +055 kg for reinforcements)
bull Fin Box 06 kg (Tuttle std and reinforcements)
bull Footstrap plugs (times12) 04 kg
bull Fibre patches around fitting 05 kg (1 m2)
So total weight of fittings is 38 kg1 For filling and painting the estimates are
Filler =02 kgPaint =05 kg maximum estimate assuming 1 litres of paint
Hencetotal weight = 143 kg
excluding centreboard (which weighs 085 kg) footstraps amp finNote an additional full lamination adds 10Y g where Y is the fibre weight is gmminus2
ie 130 gmminus2 glass fibre adds a further 13 kg For comparison the claimed weightsof currently available production boards are Starboard Phantom 139 kg Exocet Warp135 kg and Mistral One Design 155 kg
1will lose about 35 kg when polystyrene is routed out
Table 12 lists the actual costs of the materials that go into the board If you where tobuild in glass only you could probably get it down to $1300 There is excess HDF but2 sheets isnrsquot quite enough There is also the cost of consumables
bull paint brushes rollers
bull sandpaper
bull masking tape
bull gloves masks
bull material for templates
bull measuring beakers
I didnrsquot keep track of the cost of the consumables but itrsquos of the order $100 The othercosts include footstraps which for a the full 8 straps at $25 each would be $200 (luckilyI had some old ones I could use) and a fin $150 One thing I hadnrsquot factored in was theuniextension I tried to adapt an existing uni by replacing the pin to suit the rsx trackbut it seems the pin is unique to the rsx track so I could not source a suitable pin Inthe end I had to buy a new rsx mastfoot which was incompatible with my extensionstherefore a new extension too all up another $120
I have not included the cost of any tools I had to buy eg sur-form set-square andany of the electronics associated with the vacuum pump and hotwire
Table 12 Actual material costs in Australian dollars August 2008 For comparisonExocet Warp 380 raceboard $3500 Starboard formula $3150 Starboard Futura (freerideboard) $2500 or Neil Pryde X9 - 490cm mast $1600 For the complete board also factorin footstraps and fin and possibly the unimast extension These items take the costto around $2000 which is more than a Exocet Kona My point is you have to have acompelling reason to build it yourself other than cost
110 Time required to build
This was the most challenging aspect and I would advise anyone thinking of buildingto realistically consider whether they have the time available to complete the projectFor me the project changed from being enjoyable to a chore at about the 75 completemark When this happens you tend to start rushing and trying to take short cuts
I made the first hotwire cut on 29 September and applied the last coat of paint on8 November Prior to starting the board Irsquod made the centre board centre board boxmast track box and finbox reinforcement I worked on these bits and pieces over about6 months on and off Also factor in the time to make the templates The following isroughly how much time was spent on each step I estimate at least 100 hours of labourmaybe closer to 200 hours
Job When DaysBuilding the centreboard Sporadically 2-3 weekendsfittings amp templatesHotwire cutting and board shaping Weekend 2 full daysLaminating 80 done Week off work amp weekend 7 full daysFinal deck top lamination Weekend 1 full dayFilling the weave and sanding Weekend 2 part daysMore surface prep Week nights 1 day equivalentPainting amp fitting gaskets melb cup 4 day long weekend couple hrsdayMore painting Before and after work 1 day equivalentFinish painting Weekend 1 full day
14
Chapter 2Centreboard
21 Design of centreboard
The physics of the flow around an aerofoil is not trivial Motivated by the desire forefficient and fast flight a great deal of scientific and engineering research has beendevoted to the problem Methods for predicting the performance of aerofoils involveapproximations which are quite accurate at low angles of attack more challenging ispredicting the stall characteristics
In designing the centreboard there are two main aspects to consider
1 the aerofoil section which includes the maximum thickness of the aerofoil andpoint of maximum thickness
2 the plan shape
Since the centreboard is a symmetric aerofoil camber and twist are zero and the para-metric design space is somewhat reduced A considerable effort can be devoted to thedesign process However it is worth keeping in mind that hand shaping techniqueswill ultimately limit your ability to accurate produce it
211 Aerofoil section
Based on wind tunnel experiments a large database of aerofoil characteristics was com-plied in the 1930rsquos by NACA (National Advisory Committee of Aeronautics nowNASA) Figure 21 shows the what is referred to as the NACA0010 aerofoil sectionThe important parameter is the maximum thickness of this aerofoil which in this caseis 10 of the chord length c (hence the 10 in NACA0010 00 means no camber) Notethe chord is the straight line joining the leading edge to the trailing edge The numbersin figure 21 refer to selected x y (mm) coordinates on the upper surface relative to theorigin at the leading edge where in this example the chord c = 170 mm which is thechord length at the root of the aerofoil (ie at the point where the centreboard is againstthe hull) Left of the vertical red line is where I used the balsa wood moulding whichjust happened to fit the NACA0010 profile quite well The maximum thickness of theaerofoil is at x = 51 mm where y = t2 = 85 and hence t = 17 mm (ie 10 of c)where t is the thickness
Figure 21 The NACA0010 aerofoil section plotted for a chord length of 170 mm Thisfigure is to scale and can be used as a template if you print the page at 100 scale
Figure 22 Contour plot of what we want to achieve with hand tools and limited skillthis is a challenge
As will be seen in the next section we will choose an elliptic planform so that thechord length progressively reduces towards the tip of the centreboard This meanswe must continuously scale down the profile in figure 21 Figure 22 shows the sur-face contour of the centreboard required to achieve a NACA0010 section at all crosssections
212 Planshape
Mathematical analysis of wings is difficult However a classic result obtained in the1930rsquos is that for unswept wings an elliptical planform gives the minimum possibledrag for a given value of lift (ie it achieves the best LiftDrag ratio) So why notuse the elliptical planform if nothing else it looks better than a rectangular shapedcentreboard
22 Construction of centreboard
The centreboard is built using laminated cedar strips wrapped in a layer of carbonglassfibre using epoxy as the resin There are several useful articles on design and construc-tion of centreboard on the Internet (see for example Philrsquos Foils amp Composites MothHardware Phil Stevenson and Design and construction of centreboards and rudders PaulZander )
I used a rough-sawn cedar weather-board and ripped strips of around 35 mm wideSince I was cutting from a weather-board I could rip pieces of different thickness andbuild up a coarse approximation to the final aerofoil section The strips were gluedwith epoxy For the leading edge I used a piece of balsa around 12 mm wide whichwas pre-shaped into an aerofoil leading edge (try a model aircraft shop)
The centreboard is shaped using an electrical sander with coarse sandpaper I onlymade a template of the root sectional profile So at the end of this stage I had a rectan-
16
Design and construction of a windsurfer longboard
Figure 23 Cedar strips (approx 35 mm wide) and rounded balsa lead leading edge
Figure 24 After laminating a layer of carbonglass
gular planform with a constant sectional profile Next I cut the elliptic planform witha jigsaw The aerofoil section needs to be progressively thinned down towards the tip(ie trying to keep the ratio lc constant to achieve the contour of figure 22) To dothis accurately yoursquod need several sectional profiles for several different locations Inthe end I couldnrsquot be bothered with trying to accurately produce figure 22 and justthinned it out by eye Figure 23 shows the centreboard at this point low spots andimperfects have been filled (pink coloured epoxy filler)
After cutting the required shape of the area that goes through the board itrsquos readyto be laminated I used 200 gmminus2 carbon fibre double thickness from the handle toaround 50 mm below the root I ended up adding an extra layer of glass (130 gmminus2) asI thought Irsquod used too much resin and wanted to soak it up I did it all in one go andwrapped it in a vacuum bag and held it under vacuum overnight while it dried Thevacuum isnrsquot essential but does improve the result A photo of the centreboard afterremoving from the vacuum bag is shown in figure 24 the excess fibre on the trailingedge is easily trimmed off with a knife and sanded smooth donrsquot make it razor shape
23 Centreboard Box
The centreboard is highly loaded when working to windward Therefore it is necessaryto reinforce the board at the location of the centreboard I chose to build what I call acentreboard box which serves the same role as the fin box that is it provides structuralsupport for the lateral loading The difference between a fin box and centreboard boxapart from size is that the centreboard box must also provide a pivot point and asufficient cavity for the centreboard to fit in when in the retracted position The side
17
Design and construction of a windsurfer longboard
walls of the box are made of 25 mm thick polyurethane foam with 2 sheets of HDFlaminate onto the surface (between each layer of foam is 130 gmminus2 glass) To providea pivot point a 5 mm thick piece of marine ply is used with a channel cut into it Thispiece is plywood is recessed into the top HDF layer which also has a channel cut intoit Figure 25 shows the foam and plywood layup and figure 26 shows details of thepivot point prior to the final lamination The final lamination is made up of a layer of200gmminus2 carbon and a layer of 130 gmminus2 glass
180 mm
25 mm urethane foam
5 mm PVC5 mm plywood
1000 mm
Figure 25 Layup of sidewall panels for centreboard box
Figure 26 Plywood reinforcement provides support for centreboard pivot
The width of the centreboard box cavity is asymp 25 mm and chocks of foam 25 mmthick are glued in between the side wall panels At the front of the box I used a trian-gular shaped piece of HDF and at the rear I used polyurethane foam shaped to followthe shape of the trailing edge of the centreboard figure 27These chocks of foam werefirst laminated with fibreglass before gluing them in between the side panels Afterusing the board a few times I discovered a small leak at the rear of the box between thecentral piece of foam and the sidewalls so Irsquod recommend also laying a layer of fibre-glass over the join By sanding or building up the strips you can adjust the amount offriction holding the centreboard
Layers of
HDF foam 25 mmpolyurethane
foam
Figure 27 Foam panels placed in between the sidewall panels
Ideally the centreboard should be a firm fit in the box otherwise when in the re-tracted position it has a tendency to flop back down particularly when bouncing over
18
Design and construction of a windsurfer longboard
Figure 28 Centre board box bottom view
pivot pin of centreboard
Deck
sidewall panel
friction strip
Figure 29 Friction strip which fits in the channel in the centreboard box
choppy waters Unless you are able to achieve high tolerances when manufacturingcentreboard box it is difficult to achieve a tight fit without having the centreboard jamwhen it is rotating It is better to leave some clearance in the centreboard box then packthe centreboard tight with what I call ldquofriction stripsrdquo These are simply strips about5 mm thick which are placed in the rebatted channel (shown in figure 26) after the cen-treboard is in place Initially I used plywood but found it wore out quickly so I endedup using sections from a sail batten built up to the required thickness with layers ofcarbon fibre and shown in figure 29 The strips are screwed down to the deck of theboard Make sure you place an adequate screw plug in the board Make the strips longenough so that they are in contact with the centreboard pivot pin figure 29
19
Chapter 3Mast track fin-box and footstrap plugs
When placing fittings into the board it is important to reinforce the board around thefitting using a higher density foam than the polystyrene core My approach was tobuild up a block of foam around each fitting I used 25 mm polyurethane 5 mm HDFand fibreglass to make sandwich panels that go around each part These panels helpspread the load and increase the top surface area of each part so there is more areafor the deck or hull lamination to adhere to I prepared all these parts before I startedbuilding the actual board This gave me practise in vacuum bagging on a small scale
31 Mast track
The part I had most difficulty getting was the sliding mast track I was quoted $200 fora mistral one-design track or $80 for a RSX track I opted for the RSX the only draw-back is that they donrsquot have as much travel as a traditional raceboard track figure 31Figure 32 shows the mast-track-box made out of high density foam The actual trackis screwed into the channel I used footstrap plugs as the anchor points for the screws
Figure 31 RSX mast track
32 Finbox and Footstrap plugs
I used a standard tuttle finbox You may wish to use a deep one instead but I believeformula style fins (or a fin gt 50 cm) are unnecessary for longboards so a standardshould do Foam sandwich panels are packed around the finbox and footstrap plugsto provide reinforcement figure 33
20
Design and construction of a windsurfer longboard
Figure 32 Mast track box made of urethaneHDFfibre sandwich
Figure 33 Finbox and footstrap plug reinforcements made of urethaneHDFfibresandwich
21
Chapter 4Board Construction
41 Shaping
The board is shaped as much as possible using a hotwire cutter Since the hotwire is astraight wire you cannot shaped doubly curved surfaces with it eg rails and deck forthese areas I shaped with sandpaper The sequence of shaping is as follows
1 hotwire cut rocker
2 hotwire cut vee
3 hotwire cut planshape
4 hotwire cut linear approximation of rail profile
5 hand sand deck and rail to required curve
The idea is to do as much shaping with a hotwire using templates to guide the cutEven when it came to fairing in the deck and rails I used cardboard templates of thecurve
411 Templates
I used A3 paper to print out templates of the centre-line profile (ie rocker) and plan-shape When creating these templates I subtracted the thickness of the HDF foam offthe template outline so that the specifications given earlier are for the built board notthe core To plot the profiles in full scale I used the vector graphics language AsymptoteSince an A3 piece of paper is 594times 420 mm I printed a section of the profile on eachpage then joined them all together These are the pdf files containing the templates
bull core-centre-linepdf
bull planshape-portpdf
bull planshape-starpdf 1
1Note the maximum half-width of the board is wider than an A3 sheet of paper so the planshape inthese files is referenced to a line offset 25 mm from the centre-line
22
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
t(x)
z
l = 3800
tm = 180
ρ(x)
ρ = 270
x
1000 2000 3000
Figure 11 Centre-line profile
8
Design and construction of a windsurfer longboard
Figure 12 The board used as a rough guide for the design The actual board I designedis quite different the only dimension I matched was the maximum rocker (nose kick)Itrsquos good to have something to reference your design against just to ensure you donrsquotdesign something ldquooff the scalerdquo
9
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
x (mm)
0
y (mm)
l = 3800mm
w
Stern
500 1000 1500 2000 2500 3000 3500-500
0
500
170 320 1375 2180
1580535
Figure 13 Planshape
10
Design and construction of a windsurfer longboard
yw2
zt
05
0-1 -05 0 05 1
1
Figure 14 Spline defining the deck and rail normalised curve
x=100
x=250
x=500
x=750
x=1000
x=1500
x=1900
x=750
x=1000
x=1500
x=1900
z 100
150
200
50
0-350 -250 -150 -50 y 50 150 250 350
Figure 15 Individual cross sectional profiles for the back half of the board Noteconstant vee of 1o Note in these figures Irsquom really plotting zminus ρ ie Irsquom not includingthe effect of the rocker which would shift each successive curve upwards as you moveforward along the board
x=2000
x=2500
x=3000
x=3250
x=3500
x=3600
x=3700
x=3750
x=3250
z 100
150
200
50
0-350 -250 -150 -50 y 50 150 250 350
Figure 16 Individual cross sectional profiles for the front half of the board Noteconstant vee of 1o
11
Design and construction of a windsurfer longboard
18 Design weight
Summarising the design volume and total surface area are
Volume = 252 l and Area = 45 m2
The construction will be carbon sandwich with the following layup 200 gmminus2 car-bon fibre then high density foam (HDF) 80 gmminus3 with a thickness of 5 mm then anothercarbon layer (200gmminus2) Epoxy resin will be used and assuming a fibre to resin ratio of40 60 (see FGI data) then each layer of carbon will require 300 gmminus2 of resin Hencean individual carbon lamination will weigh 500 gmminus2 (note FGI quotes 480) The HDFwill add 80times 5times 10minus3 = 400 gmminus2 So HDF sandwiched between two layers of carbonthe skin weight is 45times (2times 500 + 400) gmminus2 which gives a total of
carbon sandwich weight = 63 kg
The core is low density polystyrene with a density of 14 kgmminus3 which gives a
core weight = 0252times 14 = 35 kg
and hence the subtotal of board without fittings and paint is 98 kgThe other components are estimated to weigh
bull centreboard case 12 kg (HDF carbon construction)
bull Mast track 11 kg (055 kg RSX part +055 kg for reinforcements)
bull Fin Box 06 kg (Tuttle std and reinforcements)
bull Footstrap plugs (times12) 04 kg
bull Fibre patches around fitting 05 kg (1 m2)
So total weight of fittings is 38 kg1 For filling and painting the estimates are
Filler =02 kgPaint =05 kg maximum estimate assuming 1 litres of paint
Hencetotal weight = 143 kg
excluding centreboard (which weighs 085 kg) footstraps amp finNote an additional full lamination adds 10Y g where Y is the fibre weight is gmminus2
ie 130 gmminus2 glass fibre adds a further 13 kg For comparison the claimed weightsof currently available production boards are Starboard Phantom 139 kg Exocet Warp135 kg and Mistral One Design 155 kg
1will lose about 35 kg when polystyrene is routed out
Table 12 lists the actual costs of the materials that go into the board If you where tobuild in glass only you could probably get it down to $1300 There is excess HDF but2 sheets isnrsquot quite enough There is also the cost of consumables
bull paint brushes rollers
bull sandpaper
bull masking tape
bull gloves masks
bull material for templates
bull measuring beakers
I didnrsquot keep track of the cost of the consumables but itrsquos of the order $100 The othercosts include footstraps which for a the full 8 straps at $25 each would be $200 (luckilyI had some old ones I could use) and a fin $150 One thing I hadnrsquot factored in was theuniextension I tried to adapt an existing uni by replacing the pin to suit the rsx trackbut it seems the pin is unique to the rsx track so I could not source a suitable pin Inthe end I had to buy a new rsx mastfoot which was incompatible with my extensionstherefore a new extension too all up another $120
I have not included the cost of any tools I had to buy eg sur-form set-square andany of the electronics associated with the vacuum pump and hotwire
Table 12 Actual material costs in Australian dollars August 2008 For comparisonExocet Warp 380 raceboard $3500 Starboard formula $3150 Starboard Futura (freerideboard) $2500 or Neil Pryde X9 - 490cm mast $1600 For the complete board also factorin footstraps and fin and possibly the unimast extension These items take the costto around $2000 which is more than a Exocet Kona My point is you have to have acompelling reason to build it yourself other than cost
110 Time required to build
This was the most challenging aspect and I would advise anyone thinking of buildingto realistically consider whether they have the time available to complete the projectFor me the project changed from being enjoyable to a chore at about the 75 completemark When this happens you tend to start rushing and trying to take short cuts
I made the first hotwire cut on 29 September and applied the last coat of paint on8 November Prior to starting the board Irsquod made the centre board centre board boxmast track box and finbox reinforcement I worked on these bits and pieces over about6 months on and off Also factor in the time to make the templates The following isroughly how much time was spent on each step I estimate at least 100 hours of labourmaybe closer to 200 hours
Job When DaysBuilding the centreboard Sporadically 2-3 weekendsfittings amp templatesHotwire cutting and board shaping Weekend 2 full daysLaminating 80 done Week off work amp weekend 7 full daysFinal deck top lamination Weekend 1 full dayFilling the weave and sanding Weekend 2 part daysMore surface prep Week nights 1 day equivalentPainting amp fitting gaskets melb cup 4 day long weekend couple hrsdayMore painting Before and after work 1 day equivalentFinish painting Weekend 1 full day
14
Chapter 2Centreboard
21 Design of centreboard
The physics of the flow around an aerofoil is not trivial Motivated by the desire forefficient and fast flight a great deal of scientific and engineering research has beendevoted to the problem Methods for predicting the performance of aerofoils involveapproximations which are quite accurate at low angles of attack more challenging ispredicting the stall characteristics
In designing the centreboard there are two main aspects to consider
1 the aerofoil section which includes the maximum thickness of the aerofoil andpoint of maximum thickness
2 the plan shape
Since the centreboard is a symmetric aerofoil camber and twist are zero and the para-metric design space is somewhat reduced A considerable effort can be devoted to thedesign process However it is worth keeping in mind that hand shaping techniqueswill ultimately limit your ability to accurate produce it
211 Aerofoil section
Based on wind tunnel experiments a large database of aerofoil characteristics was com-plied in the 1930rsquos by NACA (National Advisory Committee of Aeronautics nowNASA) Figure 21 shows the what is referred to as the NACA0010 aerofoil sectionThe important parameter is the maximum thickness of this aerofoil which in this caseis 10 of the chord length c (hence the 10 in NACA0010 00 means no camber) Notethe chord is the straight line joining the leading edge to the trailing edge The numbersin figure 21 refer to selected x y (mm) coordinates on the upper surface relative to theorigin at the leading edge where in this example the chord c = 170 mm which is thechord length at the root of the aerofoil (ie at the point where the centreboard is againstthe hull) Left of the vertical red line is where I used the balsa wood moulding whichjust happened to fit the NACA0010 profile quite well The maximum thickness of theaerofoil is at x = 51 mm where y = t2 = 85 and hence t = 17 mm (ie 10 of c)where t is the thickness
Figure 21 The NACA0010 aerofoil section plotted for a chord length of 170 mm Thisfigure is to scale and can be used as a template if you print the page at 100 scale
Figure 22 Contour plot of what we want to achieve with hand tools and limited skillthis is a challenge
As will be seen in the next section we will choose an elliptic planform so that thechord length progressively reduces towards the tip of the centreboard This meanswe must continuously scale down the profile in figure 21 Figure 22 shows the sur-face contour of the centreboard required to achieve a NACA0010 section at all crosssections
212 Planshape
Mathematical analysis of wings is difficult However a classic result obtained in the1930rsquos is that for unswept wings an elliptical planform gives the minimum possibledrag for a given value of lift (ie it achieves the best LiftDrag ratio) So why notuse the elliptical planform if nothing else it looks better than a rectangular shapedcentreboard
22 Construction of centreboard
The centreboard is built using laminated cedar strips wrapped in a layer of carbonglassfibre using epoxy as the resin There are several useful articles on design and construc-tion of centreboard on the Internet (see for example Philrsquos Foils amp Composites MothHardware Phil Stevenson and Design and construction of centreboards and rudders PaulZander )
I used a rough-sawn cedar weather-board and ripped strips of around 35 mm wideSince I was cutting from a weather-board I could rip pieces of different thickness andbuild up a coarse approximation to the final aerofoil section The strips were gluedwith epoxy For the leading edge I used a piece of balsa around 12 mm wide whichwas pre-shaped into an aerofoil leading edge (try a model aircraft shop)
The centreboard is shaped using an electrical sander with coarse sandpaper I onlymade a template of the root sectional profile So at the end of this stage I had a rectan-
16
Design and construction of a windsurfer longboard
Figure 23 Cedar strips (approx 35 mm wide) and rounded balsa lead leading edge
Figure 24 After laminating a layer of carbonglass
gular planform with a constant sectional profile Next I cut the elliptic planform witha jigsaw The aerofoil section needs to be progressively thinned down towards the tip(ie trying to keep the ratio lc constant to achieve the contour of figure 22) To dothis accurately yoursquod need several sectional profiles for several different locations Inthe end I couldnrsquot be bothered with trying to accurately produce figure 22 and justthinned it out by eye Figure 23 shows the centreboard at this point low spots andimperfects have been filled (pink coloured epoxy filler)
After cutting the required shape of the area that goes through the board itrsquos readyto be laminated I used 200 gmminus2 carbon fibre double thickness from the handle toaround 50 mm below the root I ended up adding an extra layer of glass (130 gmminus2) asI thought Irsquod used too much resin and wanted to soak it up I did it all in one go andwrapped it in a vacuum bag and held it under vacuum overnight while it dried Thevacuum isnrsquot essential but does improve the result A photo of the centreboard afterremoving from the vacuum bag is shown in figure 24 the excess fibre on the trailingedge is easily trimmed off with a knife and sanded smooth donrsquot make it razor shape
23 Centreboard Box
The centreboard is highly loaded when working to windward Therefore it is necessaryto reinforce the board at the location of the centreboard I chose to build what I call acentreboard box which serves the same role as the fin box that is it provides structuralsupport for the lateral loading The difference between a fin box and centreboard boxapart from size is that the centreboard box must also provide a pivot point and asufficient cavity for the centreboard to fit in when in the retracted position The side
17
Design and construction of a windsurfer longboard
walls of the box are made of 25 mm thick polyurethane foam with 2 sheets of HDFlaminate onto the surface (between each layer of foam is 130 gmminus2 glass) To providea pivot point a 5 mm thick piece of marine ply is used with a channel cut into it Thispiece is plywood is recessed into the top HDF layer which also has a channel cut intoit Figure 25 shows the foam and plywood layup and figure 26 shows details of thepivot point prior to the final lamination The final lamination is made up of a layer of200gmminus2 carbon and a layer of 130 gmminus2 glass
180 mm
25 mm urethane foam
5 mm PVC5 mm plywood
1000 mm
Figure 25 Layup of sidewall panels for centreboard box
Figure 26 Plywood reinforcement provides support for centreboard pivot
The width of the centreboard box cavity is asymp 25 mm and chocks of foam 25 mmthick are glued in between the side wall panels At the front of the box I used a trian-gular shaped piece of HDF and at the rear I used polyurethane foam shaped to followthe shape of the trailing edge of the centreboard figure 27These chocks of foam werefirst laminated with fibreglass before gluing them in between the side panels Afterusing the board a few times I discovered a small leak at the rear of the box between thecentral piece of foam and the sidewalls so Irsquod recommend also laying a layer of fibre-glass over the join By sanding or building up the strips you can adjust the amount offriction holding the centreboard
Layers of
HDF foam 25 mmpolyurethane
foam
Figure 27 Foam panels placed in between the sidewall panels
Ideally the centreboard should be a firm fit in the box otherwise when in the re-tracted position it has a tendency to flop back down particularly when bouncing over
18
Design and construction of a windsurfer longboard
Figure 28 Centre board box bottom view
pivot pin of centreboard
Deck
sidewall panel
friction strip
Figure 29 Friction strip which fits in the channel in the centreboard box
choppy waters Unless you are able to achieve high tolerances when manufacturingcentreboard box it is difficult to achieve a tight fit without having the centreboard jamwhen it is rotating It is better to leave some clearance in the centreboard box then packthe centreboard tight with what I call ldquofriction stripsrdquo These are simply strips about5 mm thick which are placed in the rebatted channel (shown in figure 26) after the cen-treboard is in place Initially I used plywood but found it wore out quickly so I endedup using sections from a sail batten built up to the required thickness with layers ofcarbon fibre and shown in figure 29 The strips are screwed down to the deck of theboard Make sure you place an adequate screw plug in the board Make the strips longenough so that they are in contact with the centreboard pivot pin figure 29
19
Chapter 3Mast track fin-box and footstrap plugs
When placing fittings into the board it is important to reinforce the board around thefitting using a higher density foam than the polystyrene core My approach was tobuild up a block of foam around each fitting I used 25 mm polyurethane 5 mm HDFand fibreglass to make sandwich panels that go around each part These panels helpspread the load and increase the top surface area of each part so there is more areafor the deck or hull lamination to adhere to I prepared all these parts before I startedbuilding the actual board This gave me practise in vacuum bagging on a small scale
31 Mast track
The part I had most difficulty getting was the sliding mast track I was quoted $200 fora mistral one-design track or $80 for a RSX track I opted for the RSX the only draw-back is that they donrsquot have as much travel as a traditional raceboard track figure 31Figure 32 shows the mast-track-box made out of high density foam The actual trackis screwed into the channel I used footstrap plugs as the anchor points for the screws
Figure 31 RSX mast track
32 Finbox and Footstrap plugs
I used a standard tuttle finbox You may wish to use a deep one instead but I believeformula style fins (or a fin gt 50 cm) are unnecessary for longboards so a standardshould do Foam sandwich panels are packed around the finbox and footstrap plugsto provide reinforcement figure 33
20
Design and construction of a windsurfer longboard
Figure 32 Mast track box made of urethaneHDFfibre sandwich
Figure 33 Finbox and footstrap plug reinforcements made of urethaneHDFfibresandwich
21
Chapter 4Board Construction
41 Shaping
The board is shaped as much as possible using a hotwire cutter Since the hotwire is astraight wire you cannot shaped doubly curved surfaces with it eg rails and deck forthese areas I shaped with sandpaper The sequence of shaping is as follows
1 hotwire cut rocker
2 hotwire cut vee
3 hotwire cut planshape
4 hotwire cut linear approximation of rail profile
5 hand sand deck and rail to required curve
The idea is to do as much shaping with a hotwire using templates to guide the cutEven when it came to fairing in the deck and rails I used cardboard templates of thecurve
411 Templates
I used A3 paper to print out templates of the centre-line profile (ie rocker) and plan-shape When creating these templates I subtracted the thickness of the HDF foam offthe template outline so that the specifications given earlier are for the built board notthe core To plot the profiles in full scale I used the vector graphics language AsymptoteSince an A3 piece of paper is 594times 420 mm I printed a section of the profile on eachpage then joined them all together These are the pdf files containing the templates
bull core-centre-linepdf
bull planshape-portpdf
bull planshape-starpdf 1
1Note the maximum half-width of the board is wider than an A3 sheet of paper so the planshape inthese files is referenced to a line offset 25 mm from the centre-line
22
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
Figure 12 The board used as a rough guide for the design The actual board I designedis quite different the only dimension I matched was the maximum rocker (nose kick)Itrsquos good to have something to reference your design against just to ensure you donrsquotdesign something ldquooff the scalerdquo
9
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
x (mm)
0
y (mm)
l = 3800mm
w
Stern
500 1000 1500 2000 2500 3000 3500-500
0
500
170 320 1375 2180
1580535
Figure 13 Planshape
10
Design and construction of a windsurfer longboard
yw2
zt
05
0-1 -05 0 05 1
1
Figure 14 Spline defining the deck and rail normalised curve
x=100
x=250
x=500
x=750
x=1000
x=1500
x=1900
x=750
x=1000
x=1500
x=1900
z 100
150
200
50
0-350 -250 -150 -50 y 50 150 250 350
Figure 15 Individual cross sectional profiles for the back half of the board Noteconstant vee of 1o Note in these figures Irsquom really plotting zminus ρ ie Irsquom not includingthe effect of the rocker which would shift each successive curve upwards as you moveforward along the board
x=2000
x=2500
x=3000
x=3250
x=3500
x=3600
x=3700
x=3750
x=3250
z 100
150
200
50
0-350 -250 -150 -50 y 50 150 250 350
Figure 16 Individual cross sectional profiles for the front half of the board Noteconstant vee of 1o
11
Design and construction of a windsurfer longboard
18 Design weight
Summarising the design volume and total surface area are
Volume = 252 l and Area = 45 m2
The construction will be carbon sandwich with the following layup 200 gmminus2 car-bon fibre then high density foam (HDF) 80 gmminus3 with a thickness of 5 mm then anothercarbon layer (200gmminus2) Epoxy resin will be used and assuming a fibre to resin ratio of40 60 (see FGI data) then each layer of carbon will require 300 gmminus2 of resin Hencean individual carbon lamination will weigh 500 gmminus2 (note FGI quotes 480) The HDFwill add 80times 5times 10minus3 = 400 gmminus2 So HDF sandwiched between two layers of carbonthe skin weight is 45times (2times 500 + 400) gmminus2 which gives a total of
carbon sandwich weight = 63 kg
The core is low density polystyrene with a density of 14 kgmminus3 which gives a
core weight = 0252times 14 = 35 kg
and hence the subtotal of board without fittings and paint is 98 kgThe other components are estimated to weigh
bull centreboard case 12 kg (HDF carbon construction)
bull Mast track 11 kg (055 kg RSX part +055 kg for reinforcements)
bull Fin Box 06 kg (Tuttle std and reinforcements)
bull Footstrap plugs (times12) 04 kg
bull Fibre patches around fitting 05 kg (1 m2)
So total weight of fittings is 38 kg1 For filling and painting the estimates are
Filler =02 kgPaint =05 kg maximum estimate assuming 1 litres of paint
Hencetotal weight = 143 kg
excluding centreboard (which weighs 085 kg) footstraps amp finNote an additional full lamination adds 10Y g where Y is the fibre weight is gmminus2
ie 130 gmminus2 glass fibre adds a further 13 kg For comparison the claimed weightsof currently available production boards are Starboard Phantom 139 kg Exocet Warp135 kg and Mistral One Design 155 kg
1will lose about 35 kg when polystyrene is routed out
Table 12 lists the actual costs of the materials that go into the board If you where tobuild in glass only you could probably get it down to $1300 There is excess HDF but2 sheets isnrsquot quite enough There is also the cost of consumables
bull paint brushes rollers
bull sandpaper
bull masking tape
bull gloves masks
bull material for templates
bull measuring beakers
I didnrsquot keep track of the cost of the consumables but itrsquos of the order $100 The othercosts include footstraps which for a the full 8 straps at $25 each would be $200 (luckilyI had some old ones I could use) and a fin $150 One thing I hadnrsquot factored in was theuniextension I tried to adapt an existing uni by replacing the pin to suit the rsx trackbut it seems the pin is unique to the rsx track so I could not source a suitable pin Inthe end I had to buy a new rsx mastfoot which was incompatible with my extensionstherefore a new extension too all up another $120
I have not included the cost of any tools I had to buy eg sur-form set-square andany of the electronics associated with the vacuum pump and hotwire
Table 12 Actual material costs in Australian dollars August 2008 For comparisonExocet Warp 380 raceboard $3500 Starboard formula $3150 Starboard Futura (freerideboard) $2500 or Neil Pryde X9 - 490cm mast $1600 For the complete board also factorin footstraps and fin and possibly the unimast extension These items take the costto around $2000 which is more than a Exocet Kona My point is you have to have acompelling reason to build it yourself other than cost
110 Time required to build
This was the most challenging aspect and I would advise anyone thinking of buildingto realistically consider whether they have the time available to complete the projectFor me the project changed from being enjoyable to a chore at about the 75 completemark When this happens you tend to start rushing and trying to take short cuts
I made the first hotwire cut on 29 September and applied the last coat of paint on8 November Prior to starting the board Irsquod made the centre board centre board boxmast track box and finbox reinforcement I worked on these bits and pieces over about6 months on and off Also factor in the time to make the templates The following isroughly how much time was spent on each step I estimate at least 100 hours of labourmaybe closer to 200 hours
Job When DaysBuilding the centreboard Sporadically 2-3 weekendsfittings amp templatesHotwire cutting and board shaping Weekend 2 full daysLaminating 80 done Week off work amp weekend 7 full daysFinal deck top lamination Weekend 1 full dayFilling the weave and sanding Weekend 2 part daysMore surface prep Week nights 1 day equivalentPainting amp fitting gaskets melb cup 4 day long weekend couple hrsdayMore painting Before and after work 1 day equivalentFinish painting Weekend 1 full day
14
Chapter 2Centreboard
21 Design of centreboard
The physics of the flow around an aerofoil is not trivial Motivated by the desire forefficient and fast flight a great deal of scientific and engineering research has beendevoted to the problem Methods for predicting the performance of aerofoils involveapproximations which are quite accurate at low angles of attack more challenging ispredicting the stall characteristics
In designing the centreboard there are two main aspects to consider
1 the aerofoil section which includes the maximum thickness of the aerofoil andpoint of maximum thickness
2 the plan shape
Since the centreboard is a symmetric aerofoil camber and twist are zero and the para-metric design space is somewhat reduced A considerable effort can be devoted to thedesign process However it is worth keeping in mind that hand shaping techniqueswill ultimately limit your ability to accurate produce it
211 Aerofoil section
Based on wind tunnel experiments a large database of aerofoil characteristics was com-plied in the 1930rsquos by NACA (National Advisory Committee of Aeronautics nowNASA) Figure 21 shows the what is referred to as the NACA0010 aerofoil sectionThe important parameter is the maximum thickness of this aerofoil which in this caseis 10 of the chord length c (hence the 10 in NACA0010 00 means no camber) Notethe chord is the straight line joining the leading edge to the trailing edge The numbersin figure 21 refer to selected x y (mm) coordinates on the upper surface relative to theorigin at the leading edge where in this example the chord c = 170 mm which is thechord length at the root of the aerofoil (ie at the point where the centreboard is againstthe hull) Left of the vertical red line is where I used the balsa wood moulding whichjust happened to fit the NACA0010 profile quite well The maximum thickness of theaerofoil is at x = 51 mm where y = t2 = 85 and hence t = 17 mm (ie 10 of c)where t is the thickness
Figure 21 The NACA0010 aerofoil section plotted for a chord length of 170 mm Thisfigure is to scale and can be used as a template if you print the page at 100 scale
Figure 22 Contour plot of what we want to achieve with hand tools and limited skillthis is a challenge
As will be seen in the next section we will choose an elliptic planform so that thechord length progressively reduces towards the tip of the centreboard This meanswe must continuously scale down the profile in figure 21 Figure 22 shows the sur-face contour of the centreboard required to achieve a NACA0010 section at all crosssections
212 Planshape
Mathematical analysis of wings is difficult However a classic result obtained in the1930rsquos is that for unswept wings an elliptical planform gives the minimum possibledrag for a given value of lift (ie it achieves the best LiftDrag ratio) So why notuse the elliptical planform if nothing else it looks better than a rectangular shapedcentreboard
22 Construction of centreboard
The centreboard is built using laminated cedar strips wrapped in a layer of carbonglassfibre using epoxy as the resin There are several useful articles on design and construc-tion of centreboard on the Internet (see for example Philrsquos Foils amp Composites MothHardware Phil Stevenson and Design and construction of centreboards and rudders PaulZander )
I used a rough-sawn cedar weather-board and ripped strips of around 35 mm wideSince I was cutting from a weather-board I could rip pieces of different thickness andbuild up a coarse approximation to the final aerofoil section The strips were gluedwith epoxy For the leading edge I used a piece of balsa around 12 mm wide whichwas pre-shaped into an aerofoil leading edge (try a model aircraft shop)
The centreboard is shaped using an electrical sander with coarse sandpaper I onlymade a template of the root sectional profile So at the end of this stage I had a rectan-
16
Design and construction of a windsurfer longboard
Figure 23 Cedar strips (approx 35 mm wide) and rounded balsa lead leading edge
Figure 24 After laminating a layer of carbonglass
gular planform with a constant sectional profile Next I cut the elliptic planform witha jigsaw The aerofoil section needs to be progressively thinned down towards the tip(ie trying to keep the ratio lc constant to achieve the contour of figure 22) To dothis accurately yoursquod need several sectional profiles for several different locations Inthe end I couldnrsquot be bothered with trying to accurately produce figure 22 and justthinned it out by eye Figure 23 shows the centreboard at this point low spots andimperfects have been filled (pink coloured epoxy filler)
After cutting the required shape of the area that goes through the board itrsquos readyto be laminated I used 200 gmminus2 carbon fibre double thickness from the handle toaround 50 mm below the root I ended up adding an extra layer of glass (130 gmminus2) asI thought Irsquod used too much resin and wanted to soak it up I did it all in one go andwrapped it in a vacuum bag and held it under vacuum overnight while it dried Thevacuum isnrsquot essential but does improve the result A photo of the centreboard afterremoving from the vacuum bag is shown in figure 24 the excess fibre on the trailingedge is easily trimmed off with a knife and sanded smooth donrsquot make it razor shape
23 Centreboard Box
The centreboard is highly loaded when working to windward Therefore it is necessaryto reinforce the board at the location of the centreboard I chose to build what I call acentreboard box which serves the same role as the fin box that is it provides structuralsupport for the lateral loading The difference between a fin box and centreboard boxapart from size is that the centreboard box must also provide a pivot point and asufficient cavity for the centreboard to fit in when in the retracted position The side
17
Design and construction of a windsurfer longboard
walls of the box are made of 25 mm thick polyurethane foam with 2 sheets of HDFlaminate onto the surface (between each layer of foam is 130 gmminus2 glass) To providea pivot point a 5 mm thick piece of marine ply is used with a channel cut into it Thispiece is plywood is recessed into the top HDF layer which also has a channel cut intoit Figure 25 shows the foam and plywood layup and figure 26 shows details of thepivot point prior to the final lamination The final lamination is made up of a layer of200gmminus2 carbon and a layer of 130 gmminus2 glass
180 mm
25 mm urethane foam
5 mm PVC5 mm plywood
1000 mm
Figure 25 Layup of sidewall panels for centreboard box
Figure 26 Plywood reinforcement provides support for centreboard pivot
The width of the centreboard box cavity is asymp 25 mm and chocks of foam 25 mmthick are glued in between the side wall panels At the front of the box I used a trian-gular shaped piece of HDF and at the rear I used polyurethane foam shaped to followthe shape of the trailing edge of the centreboard figure 27These chocks of foam werefirst laminated with fibreglass before gluing them in between the side panels Afterusing the board a few times I discovered a small leak at the rear of the box between thecentral piece of foam and the sidewalls so Irsquod recommend also laying a layer of fibre-glass over the join By sanding or building up the strips you can adjust the amount offriction holding the centreboard
Layers of
HDF foam 25 mmpolyurethane
foam
Figure 27 Foam panels placed in between the sidewall panels
Ideally the centreboard should be a firm fit in the box otherwise when in the re-tracted position it has a tendency to flop back down particularly when bouncing over
18
Design and construction of a windsurfer longboard
Figure 28 Centre board box bottom view
pivot pin of centreboard
Deck
sidewall panel
friction strip
Figure 29 Friction strip which fits in the channel in the centreboard box
choppy waters Unless you are able to achieve high tolerances when manufacturingcentreboard box it is difficult to achieve a tight fit without having the centreboard jamwhen it is rotating It is better to leave some clearance in the centreboard box then packthe centreboard tight with what I call ldquofriction stripsrdquo These are simply strips about5 mm thick which are placed in the rebatted channel (shown in figure 26) after the cen-treboard is in place Initially I used plywood but found it wore out quickly so I endedup using sections from a sail batten built up to the required thickness with layers ofcarbon fibre and shown in figure 29 The strips are screwed down to the deck of theboard Make sure you place an adequate screw plug in the board Make the strips longenough so that they are in contact with the centreboard pivot pin figure 29
19
Chapter 3Mast track fin-box and footstrap plugs
When placing fittings into the board it is important to reinforce the board around thefitting using a higher density foam than the polystyrene core My approach was tobuild up a block of foam around each fitting I used 25 mm polyurethane 5 mm HDFand fibreglass to make sandwich panels that go around each part These panels helpspread the load and increase the top surface area of each part so there is more areafor the deck or hull lamination to adhere to I prepared all these parts before I startedbuilding the actual board This gave me practise in vacuum bagging on a small scale
31 Mast track
The part I had most difficulty getting was the sliding mast track I was quoted $200 fora mistral one-design track or $80 for a RSX track I opted for the RSX the only draw-back is that they donrsquot have as much travel as a traditional raceboard track figure 31Figure 32 shows the mast-track-box made out of high density foam The actual trackis screwed into the channel I used footstrap plugs as the anchor points for the screws
Figure 31 RSX mast track
32 Finbox and Footstrap plugs
I used a standard tuttle finbox You may wish to use a deep one instead but I believeformula style fins (or a fin gt 50 cm) are unnecessary for longboards so a standardshould do Foam sandwich panels are packed around the finbox and footstrap plugsto provide reinforcement figure 33
20
Design and construction of a windsurfer longboard
Figure 32 Mast track box made of urethaneHDFfibre sandwich
Figure 33 Finbox and footstrap plug reinforcements made of urethaneHDFfibresandwich
21
Chapter 4Board Construction
41 Shaping
The board is shaped as much as possible using a hotwire cutter Since the hotwire is astraight wire you cannot shaped doubly curved surfaces with it eg rails and deck forthese areas I shaped with sandpaper The sequence of shaping is as follows
1 hotwire cut rocker
2 hotwire cut vee
3 hotwire cut planshape
4 hotwire cut linear approximation of rail profile
5 hand sand deck and rail to required curve
The idea is to do as much shaping with a hotwire using templates to guide the cutEven when it came to fairing in the deck and rails I used cardboard templates of thecurve
411 Templates
I used A3 paper to print out templates of the centre-line profile (ie rocker) and plan-shape When creating these templates I subtracted the thickness of the HDF foam offthe template outline so that the specifications given earlier are for the built board notthe core To plot the profiles in full scale I used the vector graphics language AsymptoteSince an A3 piece of paper is 594times 420 mm I printed a section of the profile on eachpage then joined them all together These are the pdf files containing the templates
bull core-centre-linepdf
bull planshape-portpdf
bull planshape-starpdf 1
1Note the maximum half-width of the board is wider than an A3 sheet of paper so the planshape inthese files is referenced to a line offset 25 mm from the centre-line
22
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
x (mm)
0
y (mm)
l = 3800mm
w
Stern
500 1000 1500 2000 2500 3000 3500-500
0
500
170 320 1375 2180
1580535
Figure 13 Planshape
10
Design and construction of a windsurfer longboard
yw2
zt
05
0-1 -05 0 05 1
1
Figure 14 Spline defining the deck and rail normalised curve
x=100
x=250
x=500
x=750
x=1000
x=1500
x=1900
x=750
x=1000
x=1500
x=1900
z 100
150
200
50
0-350 -250 -150 -50 y 50 150 250 350
Figure 15 Individual cross sectional profiles for the back half of the board Noteconstant vee of 1o Note in these figures Irsquom really plotting zminus ρ ie Irsquom not includingthe effect of the rocker which would shift each successive curve upwards as you moveforward along the board
x=2000
x=2500
x=3000
x=3250
x=3500
x=3600
x=3700
x=3750
x=3250
z 100
150
200
50
0-350 -250 -150 -50 y 50 150 250 350
Figure 16 Individual cross sectional profiles for the front half of the board Noteconstant vee of 1o
11
Design and construction of a windsurfer longboard
18 Design weight
Summarising the design volume and total surface area are
Volume = 252 l and Area = 45 m2
The construction will be carbon sandwich with the following layup 200 gmminus2 car-bon fibre then high density foam (HDF) 80 gmminus3 with a thickness of 5 mm then anothercarbon layer (200gmminus2) Epoxy resin will be used and assuming a fibre to resin ratio of40 60 (see FGI data) then each layer of carbon will require 300 gmminus2 of resin Hencean individual carbon lamination will weigh 500 gmminus2 (note FGI quotes 480) The HDFwill add 80times 5times 10minus3 = 400 gmminus2 So HDF sandwiched between two layers of carbonthe skin weight is 45times (2times 500 + 400) gmminus2 which gives a total of
carbon sandwich weight = 63 kg
The core is low density polystyrene with a density of 14 kgmminus3 which gives a
core weight = 0252times 14 = 35 kg
and hence the subtotal of board without fittings and paint is 98 kgThe other components are estimated to weigh
bull centreboard case 12 kg (HDF carbon construction)
bull Mast track 11 kg (055 kg RSX part +055 kg for reinforcements)
bull Fin Box 06 kg (Tuttle std and reinforcements)
bull Footstrap plugs (times12) 04 kg
bull Fibre patches around fitting 05 kg (1 m2)
So total weight of fittings is 38 kg1 For filling and painting the estimates are
Filler =02 kgPaint =05 kg maximum estimate assuming 1 litres of paint
Hencetotal weight = 143 kg
excluding centreboard (which weighs 085 kg) footstraps amp finNote an additional full lamination adds 10Y g where Y is the fibre weight is gmminus2
ie 130 gmminus2 glass fibre adds a further 13 kg For comparison the claimed weightsof currently available production boards are Starboard Phantom 139 kg Exocet Warp135 kg and Mistral One Design 155 kg
1will lose about 35 kg when polystyrene is routed out
Table 12 lists the actual costs of the materials that go into the board If you where tobuild in glass only you could probably get it down to $1300 There is excess HDF but2 sheets isnrsquot quite enough There is also the cost of consumables
bull paint brushes rollers
bull sandpaper
bull masking tape
bull gloves masks
bull material for templates
bull measuring beakers
I didnrsquot keep track of the cost of the consumables but itrsquos of the order $100 The othercosts include footstraps which for a the full 8 straps at $25 each would be $200 (luckilyI had some old ones I could use) and a fin $150 One thing I hadnrsquot factored in was theuniextension I tried to adapt an existing uni by replacing the pin to suit the rsx trackbut it seems the pin is unique to the rsx track so I could not source a suitable pin Inthe end I had to buy a new rsx mastfoot which was incompatible with my extensionstherefore a new extension too all up another $120
I have not included the cost of any tools I had to buy eg sur-form set-square andany of the electronics associated with the vacuum pump and hotwire
Table 12 Actual material costs in Australian dollars August 2008 For comparisonExocet Warp 380 raceboard $3500 Starboard formula $3150 Starboard Futura (freerideboard) $2500 or Neil Pryde X9 - 490cm mast $1600 For the complete board also factorin footstraps and fin and possibly the unimast extension These items take the costto around $2000 which is more than a Exocet Kona My point is you have to have acompelling reason to build it yourself other than cost
110 Time required to build
This was the most challenging aspect and I would advise anyone thinking of buildingto realistically consider whether they have the time available to complete the projectFor me the project changed from being enjoyable to a chore at about the 75 completemark When this happens you tend to start rushing and trying to take short cuts
I made the first hotwire cut on 29 September and applied the last coat of paint on8 November Prior to starting the board Irsquod made the centre board centre board boxmast track box and finbox reinforcement I worked on these bits and pieces over about6 months on and off Also factor in the time to make the templates The following isroughly how much time was spent on each step I estimate at least 100 hours of labourmaybe closer to 200 hours
Job When DaysBuilding the centreboard Sporadically 2-3 weekendsfittings amp templatesHotwire cutting and board shaping Weekend 2 full daysLaminating 80 done Week off work amp weekend 7 full daysFinal deck top lamination Weekend 1 full dayFilling the weave and sanding Weekend 2 part daysMore surface prep Week nights 1 day equivalentPainting amp fitting gaskets melb cup 4 day long weekend couple hrsdayMore painting Before and after work 1 day equivalentFinish painting Weekend 1 full day
14
Chapter 2Centreboard
21 Design of centreboard
The physics of the flow around an aerofoil is not trivial Motivated by the desire forefficient and fast flight a great deal of scientific and engineering research has beendevoted to the problem Methods for predicting the performance of aerofoils involveapproximations which are quite accurate at low angles of attack more challenging ispredicting the stall characteristics
In designing the centreboard there are two main aspects to consider
1 the aerofoil section which includes the maximum thickness of the aerofoil andpoint of maximum thickness
2 the plan shape
Since the centreboard is a symmetric aerofoil camber and twist are zero and the para-metric design space is somewhat reduced A considerable effort can be devoted to thedesign process However it is worth keeping in mind that hand shaping techniqueswill ultimately limit your ability to accurate produce it
211 Aerofoil section
Based on wind tunnel experiments a large database of aerofoil characteristics was com-plied in the 1930rsquos by NACA (National Advisory Committee of Aeronautics nowNASA) Figure 21 shows the what is referred to as the NACA0010 aerofoil sectionThe important parameter is the maximum thickness of this aerofoil which in this caseis 10 of the chord length c (hence the 10 in NACA0010 00 means no camber) Notethe chord is the straight line joining the leading edge to the trailing edge The numbersin figure 21 refer to selected x y (mm) coordinates on the upper surface relative to theorigin at the leading edge where in this example the chord c = 170 mm which is thechord length at the root of the aerofoil (ie at the point where the centreboard is againstthe hull) Left of the vertical red line is where I used the balsa wood moulding whichjust happened to fit the NACA0010 profile quite well The maximum thickness of theaerofoil is at x = 51 mm where y = t2 = 85 and hence t = 17 mm (ie 10 of c)where t is the thickness
Figure 21 The NACA0010 aerofoil section plotted for a chord length of 170 mm Thisfigure is to scale and can be used as a template if you print the page at 100 scale
Figure 22 Contour plot of what we want to achieve with hand tools and limited skillthis is a challenge
As will be seen in the next section we will choose an elliptic planform so that thechord length progressively reduces towards the tip of the centreboard This meanswe must continuously scale down the profile in figure 21 Figure 22 shows the sur-face contour of the centreboard required to achieve a NACA0010 section at all crosssections
212 Planshape
Mathematical analysis of wings is difficult However a classic result obtained in the1930rsquos is that for unswept wings an elliptical planform gives the minimum possibledrag for a given value of lift (ie it achieves the best LiftDrag ratio) So why notuse the elliptical planform if nothing else it looks better than a rectangular shapedcentreboard
22 Construction of centreboard
The centreboard is built using laminated cedar strips wrapped in a layer of carbonglassfibre using epoxy as the resin There are several useful articles on design and construc-tion of centreboard on the Internet (see for example Philrsquos Foils amp Composites MothHardware Phil Stevenson and Design and construction of centreboards and rudders PaulZander )
I used a rough-sawn cedar weather-board and ripped strips of around 35 mm wideSince I was cutting from a weather-board I could rip pieces of different thickness andbuild up a coarse approximation to the final aerofoil section The strips were gluedwith epoxy For the leading edge I used a piece of balsa around 12 mm wide whichwas pre-shaped into an aerofoil leading edge (try a model aircraft shop)
The centreboard is shaped using an electrical sander with coarse sandpaper I onlymade a template of the root sectional profile So at the end of this stage I had a rectan-
16
Design and construction of a windsurfer longboard
Figure 23 Cedar strips (approx 35 mm wide) and rounded balsa lead leading edge
Figure 24 After laminating a layer of carbonglass
gular planform with a constant sectional profile Next I cut the elliptic planform witha jigsaw The aerofoil section needs to be progressively thinned down towards the tip(ie trying to keep the ratio lc constant to achieve the contour of figure 22) To dothis accurately yoursquod need several sectional profiles for several different locations Inthe end I couldnrsquot be bothered with trying to accurately produce figure 22 and justthinned it out by eye Figure 23 shows the centreboard at this point low spots andimperfects have been filled (pink coloured epoxy filler)
After cutting the required shape of the area that goes through the board itrsquos readyto be laminated I used 200 gmminus2 carbon fibre double thickness from the handle toaround 50 mm below the root I ended up adding an extra layer of glass (130 gmminus2) asI thought Irsquod used too much resin and wanted to soak it up I did it all in one go andwrapped it in a vacuum bag and held it under vacuum overnight while it dried Thevacuum isnrsquot essential but does improve the result A photo of the centreboard afterremoving from the vacuum bag is shown in figure 24 the excess fibre on the trailingedge is easily trimmed off with a knife and sanded smooth donrsquot make it razor shape
23 Centreboard Box
The centreboard is highly loaded when working to windward Therefore it is necessaryto reinforce the board at the location of the centreboard I chose to build what I call acentreboard box which serves the same role as the fin box that is it provides structuralsupport for the lateral loading The difference between a fin box and centreboard boxapart from size is that the centreboard box must also provide a pivot point and asufficient cavity for the centreboard to fit in when in the retracted position The side
17
Design and construction of a windsurfer longboard
walls of the box are made of 25 mm thick polyurethane foam with 2 sheets of HDFlaminate onto the surface (between each layer of foam is 130 gmminus2 glass) To providea pivot point a 5 mm thick piece of marine ply is used with a channel cut into it Thispiece is plywood is recessed into the top HDF layer which also has a channel cut intoit Figure 25 shows the foam and plywood layup and figure 26 shows details of thepivot point prior to the final lamination The final lamination is made up of a layer of200gmminus2 carbon and a layer of 130 gmminus2 glass
180 mm
25 mm urethane foam
5 mm PVC5 mm plywood
1000 mm
Figure 25 Layup of sidewall panels for centreboard box
Figure 26 Plywood reinforcement provides support for centreboard pivot
The width of the centreboard box cavity is asymp 25 mm and chocks of foam 25 mmthick are glued in between the side wall panels At the front of the box I used a trian-gular shaped piece of HDF and at the rear I used polyurethane foam shaped to followthe shape of the trailing edge of the centreboard figure 27These chocks of foam werefirst laminated with fibreglass before gluing them in between the side panels Afterusing the board a few times I discovered a small leak at the rear of the box between thecentral piece of foam and the sidewalls so Irsquod recommend also laying a layer of fibre-glass over the join By sanding or building up the strips you can adjust the amount offriction holding the centreboard
Layers of
HDF foam 25 mmpolyurethane
foam
Figure 27 Foam panels placed in between the sidewall panels
Ideally the centreboard should be a firm fit in the box otherwise when in the re-tracted position it has a tendency to flop back down particularly when bouncing over
18
Design and construction of a windsurfer longboard
Figure 28 Centre board box bottom view
pivot pin of centreboard
Deck
sidewall panel
friction strip
Figure 29 Friction strip which fits in the channel in the centreboard box
choppy waters Unless you are able to achieve high tolerances when manufacturingcentreboard box it is difficult to achieve a tight fit without having the centreboard jamwhen it is rotating It is better to leave some clearance in the centreboard box then packthe centreboard tight with what I call ldquofriction stripsrdquo These are simply strips about5 mm thick which are placed in the rebatted channel (shown in figure 26) after the cen-treboard is in place Initially I used plywood but found it wore out quickly so I endedup using sections from a sail batten built up to the required thickness with layers ofcarbon fibre and shown in figure 29 The strips are screwed down to the deck of theboard Make sure you place an adequate screw plug in the board Make the strips longenough so that they are in contact with the centreboard pivot pin figure 29
19
Chapter 3Mast track fin-box and footstrap plugs
When placing fittings into the board it is important to reinforce the board around thefitting using a higher density foam than the polystyrene core My approach was tobuild up a block of foam around each fitting I used 25 mm polyurethane 5 mm HDFand fibreglass to make sandwich panels that go around each part These panels helpspread the load and increase the top surface area of each part so there is more areafor the deck or hull lamination to adhere to I prepared all these parts before I startedbuilding the actual board This gave me practise in vacuum bagging on a small scale
31 Mast track
The part I had most difficulty getting was the sliding mast track I was quoted $200 fora mistral one-design track or $80 for a RSX track I opted for the RSX the only draw-back is that they donrsquot have as much travel as a traditional raceboard track figure 31Figure 32 shows the mast-track-box made out of high density foam The actual trackis screwed into the channel I used footstrap plugs as the anchor points for the screws
Figure 31 RSX mast track
32 Finbox and Footstrap plugs
I used a standard tuttle finbox You may wish to use a deep one instead but I believeformula style fins (or a fin gt 50 cm) are unnecessary for longboards so a standardshould do Foam sandwich panels are packed around the finbox and footstrap plugsto provide reinforcement figure 33
20
Design and construction of a windsurfer longboard
Figure 32 Mast track box made of urethaneHDFfibre sandwich
Figure 33 Finbox and footstrap plug reinforcements made of urethaneHDFfibresandwich
21
Chapter 4Board Construction
41 Shaping
The board is shaped as much as possible using a hotwire cutter Since the hotwire is astraight wire you cannot shaped doubly curved surfaces with it eg rails and deck forthese areas I shaped with sandpaper The sequence of shaping is as follows
1 hotwire cut rocker
2 hotwire cut vee
3 hotwire cut planshape
4 hotwire cut linear approximation of rail profile
5 hand sand deck and rail to required curve
The idea is to do as much shaping with a hotwire using templates to guide the cutEven when it came to fairing in the deck and rails I used cardboard templates of thecurve
411 Templates
I used A3 paper to print out templates of the centre-line profile (ie rocker) and plan-shape When creating these templates I subtracted the thickness of the HDF foam offthe template outline so that the specifications given earlier are for the built board notthe core To plot the profiles in full scale I used the vector graphics language AsymptoteSince an A3 piece of paper is 594times 420 mm I printed a section of the profile on eachpage then joined them all together These are the pdf files containing the templates
bull core-centre-linepdf
bull planshape-portpdf
bull planshape-starpdf 1
1Note the maximum half-width of the board is wider than an A3 sheet of paper so the planshape inthese files is referenced to a line offset 25 mm from the centre-line
22
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
yw2
zt
05
0-1 -05 0 05 1
1
Figure 14 Spline defining the deck and rail normalised curve
x=100
x=250
x=500
x=750
x=1000
x=1500
x=1900
x=750
x=1000
x=1500
x=1900
z 100
150
200
50
0-350 -250 -150 -50 y 50 150 250 350
Figure 15 Individual cross sectional profiles for the back half of the board Noteconstant vee of 1o Note in these figures Irsquom really plotting zminus ρ ie Irsquom not includingthe effect of the rocker which would shift each successive curve upwards as you moveforward along the board
x=2000
x=2500
x=3000
x=3250
x=3500
x=3600
x=3700
x=3750
x=3250
z 100
150
200
50
0-350 -250 -150 -50 y 50 150 250 350
Figure 16 Individual cross sectional profiles for the front half of the board Noteconstant vee of 1o
11
Design and construction of a windsurfer longboard
18 Design weight
Summarising the design volume and total surface area are
Volume = 252 l and Area = 45 m2
The construction will be carbon sandwich with the following layup 200 gmminus2 car-bon fibre then high density foam (HDF) 80 gmminus3 with a thickness of 5 mm then anothercarbon layer (200gmminus2) Epoxy resin will be used and assuming a fibre to resin ratio of40 60 (see FGI data) then each layer of carbon will require 300 gmminus2 of resin Hencean individual carbon lamination will weigh 500 gmminus2 (note FGI quotes 480) The HDFwill add 80times 5times 10minus3 = 400 gmminus2 So HDF sandwiched between two layers of carbonthe skin weight is 45times (2times 500 + 400) gmminus2 which gives a total of
carbon sandwich weight = 63 kg
The core is low density polystyrene with a density of 14 kgmminus3 which gives a
core weight = 0252times 14 = 35 kg
and hence the subtotal of board without fittings and paint is 98 kgThe other components are estimated to weigh
bull centreboard case 12 kg (HDF carbon construction)
bull Mast track 11 kg (055 kg RSX part +055 kg for reinforcements)
bull Fin Box 06 kg (Tuttle std and reinforcements)
bull Footstrap plugs (times12) 04 kg
bull Fibre patches around fitting 05 kg (1 m2)
So total weight of fittings is 38 kg1 For filling and painting the estimates are
Filler =02 kgPaint =05 kg maximum estimate assuming 1 litres of paint
Hencetotal weight = 143 kg
excluding centreboard (which weighs 085 kg) footstraps amp finNote an additional full lamination adds 10Y g where Y is the fibre weight is gmminus2
ie 130 gmminus2 glass fibre adds a further 13 kg For comparison the claimed weightsof currently available production boards are Starboard Phantom 139 kg Exocet Warp135 kg and Mistral One Design 155 kg
1will lose about 35 kg when polystyrene is routed out
Table 12 lists the actual costs of the materials that go into the board If you where tobuild in glass only you could probably get it down to $1300 There is excess HDF but2 sheets isnrsquot quite enough There is also the cost of consumables
bull paint brushes rollers
bull sandpaper
bull masking tape
bull gloves masks
bull material for templates
bull measuring beakers
I didnrsquot keep track of the cost of the consumables but itrsquos of the order $100 The othercosts include footstraps which for a the full 8 straps at $25 each would be $200 (luckilyI had some old ones I could use) and a fin $150 One thing I hadnrsquot factored in was theuniextension I tried to adapt an existing uni by replacing the pin to suit the rsx trackbut it seems the pin is unique to the rsx track so I could not source a suitable pin Inthe end I had to buy a new rsx mastfoot which was incompatible with my extensionstherefore a new extension too all up another $120
I have not included the cost of any tools I had to buy eg sur-form set-square andany of the electronics associated with the vacuum pump and hotwire
Table 12 Actual material costs in Australian dollars August 2008 For comparisonExocet Warp 380 raceboard $3500 Starboard formula $3150 Starboard Futura (freerideboard) $2500 or Neil Pryde X9 - 490cm mast $1600 For the complete board also factorin footstraps and fin and possibly the unimast extension These items take the costto around $2000 which is more than a Exocet Kona My point is you have to have acompelling reason to build it yourself other than cost
110 Time required to build
This was the most challenging aspect and I would advise anyone thinking of buildingto realistically consider whether they have the time available to complete the projectFor me the project changed from being enjoyable to a chore at about the 75 completemark When this happens you tend to start rushing and trying to take short cuts
I made the first hotwire cut on 29 September and applied the last coat of paint on8 November Prior to starting the board Irsquod made the centre board centre board boxmast track box and finbox reinforcement I worked on these bits and pieces over about6 months on and off Also factor in the time to make the templates The following isroughly how much time was spent on each step I estimate at least 100 hours of labourmaybe closer to 200 hours
Job When DaysBuilding the centreboard Sporadically 2-3 weekendsfittings amp templatesHotwire cutting and board shaping Weekend 2 full daysLaminating 80 done Week off work amp weekend 7 full daysFinal deck top lamination Weekend 1 full dayFilling the weave and sanding Weekend 2 part daysMore surface prep Week nights 1 day equivalentPainting amp fitting gaskets melb cup 4 day long weekend couple hrsdayMore painting Before and after work 1 day equivalentFinish painting Weekend 1 full day
14
Chapter 2Centreboard
21 Design of centreboard
The physics of the flow around an aerofoil is not trivial Motivated by the desire forefficient and fast flight a great deal of scientific and engineering research has beendevoted to the problem Methods for predicting the performance of aerofoils involveapproximations which are quite accurate at low angles of attack more challenging ispredicting the stall characteristics
In designing the centreboard there are two main aspects to consider
1 the aerofoil section which includes the maximum thickness of the aerofoil andpoint of maximum thickness
2 the plan shape
Since the centreboard is a symmetric aerofoil camber and twist are zero and the para-metric design space is somewhat reduced A considerable effort can be devoted to thedesign process However it is worth keeping in mind that hand shaping techniqueswill ultimately limit your ability to accurate produce it
211 Aerofoil section
Based on wind tunnel experiments a large database of aerofoil characteristics was com-plied in the 1930rsquos by NACA (National Advisory Committee of Aeronautics nowNASA) Figure 21 shows the what is referred to as the NACA0010 aerofoil sectionThe important parameter is the maximum thickness of this aerofoil which in this caseis 10 of the chord length c (hence the 10 in NACA0010 00 means no camber) Notethe chord is the straight line joining the leading edge to the trailing edge The numbersin figure 21 refer to selected x y (mm) coordinates on the upper surface relative to theorigin at the leading edge where in this example the chord c = 170 mm which is thechord length at the root of the aerofoil (ie at the point where the centreboard is againstthe hull) Left of the vertical red line is where I used the balsa wood moulding whichjust happened to fit the NACA0010 profile quite well The maximum thickness of theaerofoil is at x = 51 mm where y = t2 = 85 and hence t = 17 mm (ie 10 of c)where t is the thickness
Figure 21 The NACA0010 aerofoil section plotted for a chord length of 170 mm Thisfigure is to scale and can be used as a template if you print the page at 100 scale
Figure 22 Contour plot of what we want to achieve with hand tools and limited skillthis is a challenge
As will be seen in the next section we will choose an elliptic planform so that thechord length progressively reduces towards the tip of the centreboard This meanswe must continuously scale down the profile in figure 21 Figure 22 shows the sur-face contour of the centreboard required to achieve a NACA0010 section at all crosssections
212 Planshape
Mathematical analysis of wings is difficult However a classic result obtained in the1930rsquos is that for unswept wings an elliptical planform gives the minimum possibledrag for a given value of lift (ie it achieves the best LiftDrag ratio) So why notuse the elliptical planform if nothing else it looks better than a rectangular shapedcentreboard
22 Construction of centreboard
The centreboard is built using laminated cedar strips wrapped in a layer of carbonglassfibre using epoxy as the resin There are several useful articles on design and construc-tion of centreboard on the Internet (see for example Philrsquos Foils amp Composites MothHardware Phil Stevenson and Design and construction of centreboards and rudders PaulZander )
I used a rough-sawn cedar weather-board and ripped strips of around 35 mm wideSince I was cutting from a weather-board I could rip pieces of different thickness andbuild up a coarse approximation to the final aerofoil section The strips were gluedwith epoxy For the leading edge I used a piece of balsa around 12 mm wide whichwas pre-shaped into an aerofoil leading edge (try a model aircraft shop)
The centreboard is shaped using an electrical sander with coarse sandpaper I onlymade a template of the root sectional profile So at the end of this stage I had a rectan-
16
Design and construction of a windsurfer longboard
Figure 23 Cedar strips (approx 35 mm wide) and rounded balsa lead leading edge
Figure 24 After laminating a layer of carbonglass
gular planform with a constant sectional profile Next I cut the elliptic planform witha jigsaw The aerofoil section needs to be progressively thinned down towards the tip(ie trying to keep the ratio lc constant to achieve the contour of figure 22) To dothis accurately yoursquod need several sectional profiles for several different locations Inthe end I couldnrsquot be bothered with trying to accurately produce figure 22 and justthinned it out by eye Figure 23 shows the centreboard at this point low spots andimperfects have been filled (pink coloured epoxy filler)
After cutting the required shape of the area that goes through the board itrsquos readyto be laminated I used 200 gmminus2 carbon fibre double thickness from the handle toaround 50 mm below the root I ended up adding an extra layer of glass (130 gmminus2) asI thought Irsquod used too much resin and wanted to soak it up I did it all in one go andwrapped it in a vacuum bag and held it under vacuum overnight while it dried Thevacuum isnrsquot essential but does improve the result A photo of the centreboard afterremoving from the vacuum bag is shown in figure 24 the excess fibre on the trailingedge is easily trimmed off with a knife and sanded smooth donrsquot make it razor shape
23 Centreboard Box
The centreboard is highly loaded when working to windward Therefore it is necessaryto reinforce the board at the location of the centreboard I chose to build what I call acentreboard box which serves the same role as the fin box that is it provides structuralsupport for the lateral loading The difference between a fin box and centreboard boxapart from size is that the centreboard box must also provide a pivot point and asufficient cavity for the centreboard to fit in when in the retracted position The side
17
Design and construction of a windsurfer longboard
walls of the box are made of 25 mm thick polyurethane foam with 2 sheets of HDFlaminate onto the surface (between each layer of foam is 130 gmminus2 glass) To providea pivot point a 5 mm thick piece of marine ply is used with a channel cut into it Thispiece is plywood is recessed into the top HDF layer which also has a channel cut intoit Figure 25 shows the foam and plywood layup and figure 26 shows details of thepivot point prior to the final lamination The final lamination is made up of a layer of200gmminus2 carbon and a layer of 130 gmminus2 glass
180 mm
25 mm urethane foam
5 mm PVC5 mm plywood
1000 mm
Figure 25 Layup of sidewall panels for centreboard box
Figure 26 Plywood reinforcement provides support for centreboard pivot
The width of the centreboard box cavity is asymp 25 mm and chocks of foam 25 mmthick are glued in between the side wall panels At the front of the box I used a trian-gular shaped piece of HDF and at the rear I used polyurethane foam shaped to followthe shape of the trailing edge of the centreboard figure 27These chocks of foam werefirst laminated with fibreglass before gluing them in between the side panels Afterusing the board a few times I discovered a small leak at the rear of the box between thecentral piece of foam and the sidewalls so Irsquod recommend also laying a layer of fibre-glass over the join By sanding or building up the strips you can adjust the amount offriction holding the centreboard
Layers of
HDF foam 25 mmpolyurethane
foam
Figure 27 Foam panels placed in between the sidewall panels
Ideally the centreboard should be a firm fit in the box otherwise when in the re-tracted position it has a tendency to flop back down particularly when bouncing over
18
Design and construction of a windsurfer longboard
Figure 28 Centre board box bottom view
pivot pin of centreboard
Deck
sidewall panel
friction strip
Figure 29 Friction strip which fits in the channel in the centreboard box
choppy waters Unless you are able to achieve high tolerances when manufacturingcentreboard box it is difficult to achieve a tight fit without having the centreboard jamwhen it is rotating It is better to leave some clearance in the centreboard box then packthe centreboard tight with what I call ldquofriction stripsrdquo These are simply strips about5 mm thick which are placed in the rebatted channel (shown in figure 26) after the cen-treboard is in place Initially I used plywood but found it wore out quickly so I endedup using sections from a sail batten built up to the required thickness with layers ofcarbon fibre and shown in figure 29 The strips are screwed down to the deck of theboard Make sure you place an adequate screw plug in the board Make the strips longenough so that they are in contact with the centreboard pivot pin figure 29
19
Chapter 3Mast track fin-box and footstrap plugs
When placing fittings into the board it is important to reinforce the board around thefitting using a higher density foam than the polystyrene core My approach was tobuild up a block of foam around each fitting I used 25 mm polyurethane 5 mm HDFand fibreglass to make sandwich panels that go around each part These panels helpspread the load and increase the top surface area of each part so there is more areafor the deck or hull lamination to adhere to I prepared all these parts before I startedbuilding the actual board This gave me practise in vacuum bagging on a small scale
31 Mast track
The part I had most difficulty getting was the sliding mast track I was quoted $200 fora mistral one-design track or $80 for a RSX track I opted for the RSX the only draw-back is that they donrsquot have as much travel as a traditional raceboard track figure 31Figure 32 shows the mast-track-box made out of high density foam The actual trackis screwed into the channel I used footstrap plugs as the anchor points for the screws
Figure 31 RSX mast track
32 Finbox and Footstrap plugs
I used a standard tuttle finbox You may wish to use a deep one instead but I believeformula style fins (or a fin gt 50 cm) are unnecessary for longboards so a standardshould do Foam sandwich panels are packed around the finbox and footstrap plugsto provide reinforcement figure 33
20
Design and construction of a windsurfer longboard
Figure 32 Mast track box made of urethaneHDFfibre sandwich
Figure 33 Finbox and footstrap plug reinforcements made of urethaneHDFfibresandwich
21
Chapter 4Board Construction
41 Shaping
The board is shaped as much as possible using a hotwire cutter Since the hotwire is astraight wire you cannot shaped doubly curved surfaces with it eg rails and deck forthese areas I shaped with sandpaper The sequence of shaping is as follows
1 hotwire cut rocker
2 hotwire cut vee
3 hotwire cut planshape
4 hotwire cut linear approximation of rail profile
5 hand sand deck and rail to required curve
The idea is to do as much shaping with a hotwire using templates to guide the cutEven when it came to fairing in the deck and rails I used cardboard templates of thecurve
411 Templates
I used A3 paper to print out templates of the centre-line profile (ie rocker) and plan-shape When creating these templates I subtracted the thickness of the HDF foam offthe template outline so that the specifications given earlier are for the built board notthe core To plot the profiles in full scale I used the vector graphics language AsymptoteSince an A3 piece of paper is 594times 420 mm I printed a section of the profile on eachpage then joined them all together These are the pdf files containing the templates
bull core-centre-linepdf
bull planshape-portpdf
bull planshape-starpdf 1
1Note the maximum half-width of the board is wider than an A3 sheet of paper so the planshape inthese files is referenced to a line offset 25 mm from the centre-line
22
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
18 Design weight
Summarising the design volume and total surface area are
Volume = 252 l and Area = 45 m2
The construction will be carbon sandwich with the following layup 200 gmminus2 car-bon fibre then high density foam (HDF) 80 gmminus3 with a thickness of 5 mm then anothercarbon layer (200gmminus2) Epoxy resin will be used and assuming a fibre to resin ratio of40 60 (see FGI data) then each layer of carbon will require 300 gmminus2 of resin Hencean individual carbon lamination will weigh 500 gmminus2 (note FGI quotes 480) The HDFwill add 80times 5times 10minus3 = 400 gmminus2 So HDF sandwiched between two layers of carbonthe skin weight is 45times (2times 500 + 400) gmminus2 which gives a total of
carbon sandwich weight = 63 kg
The core is low density polystyrene with a density of 14 kgmminus3 which gives a
core weight = 0252times 14 = 35 kg
and hence the subtotal of board without fittings and paint is 98 kgThe other components are estimated to weigh
bull centreboard case 12 kg (HDF carbon construction)
bull Mast track 11 kg (055 kg RSX part +055 kg for reinforcements)
bull Fin Box 06 kg (Tuttle std and reinforcements)
bull Footstrap plugs (times12) 04 kg
bull Fibre patches around fitting 05 kg (1 m2)
So total weight of fittings is 38 kg1 For filling and painting the estimates are
Filler =02 kgPaint =05 kg maximum estimate assuming 1 litres of paint
Hencetotal weight = 143 kg
excluding centreboard (which weighs 085 kg) footstraps amp finNote an additional full lamination adds 10Y g where Y is the fibre weight is gmminus2
ie 130 gmminus2 glass fibre adds a further 13 kg For comparison the claimed weightsof currently available production boards are Starboard Phantom 139 kg Exocet Warp135 kg and Mistral One Design 155 kg
1will lose about 35 kg when polystyrene is routed out
Table 12 lists the actual costs of the materials that go into the board If you where tobuild in glass only you could probably get it down to $1300 There is excess HDF but2 sheets isnrsquot quite enough There is also the cost of consumables
bull paint brushes rollers
bull sandpaper
bull masking tape
bull gloves masks
bull material for templates
bull measuring beakers
I didnrsquot keep track of the cost of the consumables but itrsquos of the order $100 The othercosts include footstraps which for a the full 8 straps at $25 each would be $200 (luckilyI had some old ones I could use) and a fin $150 One thing I hadnrsquot factored in was theuniextension I tried to adapt an existing uni by replacing the pin to suit the rsx trackbut it seems the pin is unique to the rsx track so I could not source a suitable pin Inthe end I had to buy a new rsx mastfoot which was incompatible with my extensionstherefore a new extension too all up another $120
I have not included the cost of any tools I had to buy eg sur-form set-square andany of the electronics associated with the vacuum pump and hotwire
Table 12 Actual material costs in Australian dollars August 2008 For comparisonExocet Warp 380 raceboard $3500 Starboard formula $3150 Starboard Futura (freerideboard) $2500 or Neil Pryde X9 - 490cm mast $1600 For the complete board also factorin footstraps and fin and possibly the unimast extension These items take the costto around $2000 which is more than a Exocet Kona My point is you have to have acompelling reason to build it yourself other than cost
110 Time required to build
This was the most challenging aspect and I would advise anyone thinking of buildingto realistically consider whether they have the time available to complete the projectFor me the project changed from being enjoyable to a chore at about the 75 completemark When this happens you tend to start rushing and trying to take short cuts
I made the first hotwire cut on 29 September and applied the last coat of paint on8 November Prior to starting the board Irsquod made the centre board centre board boxmast track box and finbox reinforcement I worked on these bits and pieces over about6 months on and off Also factor in the time to make the templates The following isroughly how much time was spent on each step I estimate at least 100 hours of labourmaybe closer to 200 hours
Job When DaysBuilding the centreboard Sporadically 2-3 weekendsfittings amp templatesHotwire cutting and board shaping Weekend 2 full daysLaminating 80 done Week off work amp weekend 7 full daysFinal deck top lamination Weekend 1 full dayFilling the weave and sanding Weekend 2 part daysMore surface prep Week nights 1 day equivalentPainting amp fitting gaskets melb cup 4 day long weekend couple hrsdayMore painting Before and after work 1 day equivalentFinish painting Weekend 1 full day
14
Chapter 2Centreboard
21 Design of centreboard
The physics of the flow around an aerofoil is not trivial Motivated by the desire forefficient and fast flight a great deal of scientific and engineering research has beendevoted to the problem Methods for predicting the performance of aerofoils involveapproximations which are quite accurate at low angles of attack more challenging ispredicting the stall characteristics
In designing the centreboard there are two main aspects to consider
1 the aerofoil section which includes the maximum thickness of the aerofoil andpoint of maximum thickness
2 the plan shape
Since the centreboard is a symmetric aerofoil camber and twist are zero and the para-metric design space is somewhat reduced A considerable effort can be devoted to thedesign process However it is worth keeping in mind that hand shaping techniqueswill ultimately limit your ability to accurate produce it
211 Aerofoil section
Based on wind tunnel experiments a large database of aerofoil characteristics was com-plied in the 1930rsquos by NACA (National Advisory Committee of Aeronautics nowNASA) Figure 21 shows the what is referred to as the NACA0010 aerofoil sectionThe important parameter is the maximum thickness of this aerofoil which in this caseis 10 of the chord length c (hence the 10 in NACA0010 00 means no camber) Notethe chord is the straight line joining the leading edge to the trailing edge The numbersin figure 21 refer to selected x y (mm) coordinates on the upper surface relative to theorigin at the leading edge where in this example the chord c = 170 mm which is thechord length at the root of the aerofoil (ie at the point where the centreboard is againstthe hull) Left of the vertical red line is where I used the balsa wood moulding whichjust happened to fit the NACA0010 profile quite well The maximum thickness of theaerofoil is at x = 51 mm where y = t2 = 85 and hence t = 17 mm (ie 10 of c)where t is the thickness
Figure 21 The NACA0010 aerofoil section plotted for a chord length of 170 mm Thisfigure is to scale and can be used as a template if you print the page at 100 scale
Figure 22 Contour plot of what we want to achieve with hand tools and limited skillthis is a challenge
As will be seen in the next section we will choose an elliptic planform so that thechord length progressively reduces towards the tip of the centreboard This meanswe must continuously scale down the profile in figure 21 Figure 22 shows the sur-face contour of the centreboard required to achieve a NACA0010 section at all crosssections
212 Planshape
Mathematical analysis of wings is difficult However a classic result obtained in the1930rsquos is that for unswept wings an elliptical planform gives the minimum possibledrag for a given value of lift (ie it achieves the best LiftDrag ratio) So why notuse the elliptical planform if nothing else it looks better than a rectangular shapedcentreboard
22 Construction of centreboard
The centreboard is built using laminated cedar strips wrapped in a layer of carbonglassfibre using epoxy as the resin There are several useful articles on design and construc-tion of centreboard on the Internet (see for example Philrsquos Foils amp Composites MothHardware Phil Stevenson and Design and construction of centreboards and rudders PaulZander )
I used a rough-sawn cedar weather-board and ripped strips of around 35 mm wideSince I was cutting from a weather-board I could rip pieces of different thickness andbuild up a coarse approximation to the final aerofoil section The strips were gluedwith epoxy For the leading edge I used a piece of balsa around 12 mm wide whichwas pre-shaped into an aerofoil leading edge (try a model aircraft shop)
The centreboard is shaped using an electrical sander with coarse sandpaper I onlymade a template of the root sectional profile So at the end of this stage I had a rectan-
16
Design and construction of a windsurfer longboard
Figure 23 Cedar strips (approx 35 mm wide) and rounded balsa lead leading edge
Figure 24 After laminating a layer of carbonglass
gular planform with a constant sectional profile Next I cut the elliptic planform witha jigsaw The aerofoil section needs to be progressively thinned down towards the tip(ie trying to keep the ratio lc constant to achieve the contour of figure 22) To dothis accurately yoursquod need several sectional profiles for several different locations Inthe end I couldnrsquot be bothered with trying to accurately produce figure 22 and justthinned it out by eye Figure 23 shows the centreboard at this point low spots andimperfects have been filled (pink coloured epoxy filler)
After cutting the required shape of the area that goes through the board itrsquos readyto be laminated I used 200 gmminus2 carbon fibre double thickness from the handle toaround 50 mm below the root I ended up adding an extra layer of glass (130 gmminus2) asI thought Irsquod used too much resin and wanted to soak it up I did it all in one go andwrapped it in a vacuum bag and held it under vacuum overnight while it dried Thevacuum isnrsquot essential but does improve the result A photo of the centreboard afterremoving from the vacuum bag is shown in figure 24 the excess fibre on the trailingedge is easily trimmed off with a knife and sanded smooth donrsquot make it razor shape
23 Centreboard Box
The centreboard is highly loaded when working to windward Therefore it is necessaryto reinforce the board at the location of the centreboard I chose to build what I call acentreboard box which serves the same role as the fin box that is it provides structuralsupport for the lateral loading The difference between a fin box and centreboard boxapart from size is that the centreboard box must also provide a pivot point and asufficient cavity for the centreboard to fit in when in the retracted position The side
17
Design and construction of a windsurfer longboard
walls of the box are made of 25 mm thick polyurethane foam with 2 sheets of HDFlaminate onto the surface (between each layer of foam is 130 gmminus2 glass) To providea pivot point a 5 mm thick piece of marine ply is used with a channel cut into it Thispiece is plywood is recessed into the top HDF layer which also has a channel cut intoit Figure 25 shows the foam and plywood layup and figure 26 shows details of thepivot point prior to the final lamination The final lamination is made up of a layer of200gmminus2 carbon and a layer of 130 gmminus2 glass
180 mm
25 mm urethane foam
5 mm PVC5 mm plywood
1000 mm
Figure 25 Layup of sidewall panels for centreboard box
Figure 26 Plywood reinforcement provides support for centreboard pivot
The width of the centreboard box cavity is asymp 25 mm and chocks of foam 25 mmthick are glued in between the side wall panels At the front of the box I used a trian-gular shaped piece of HDF and at the rear I used polyurethane foam shaped to followthe shape of the trailing edge of the centreboard figure 27These chocks of foam werefirst laminated with fibreglass before gluing them in between the side panels Afterusing the board a few times I discovered a small leak at the rear of the box between thecentral piece of foam and the sidewalls so Irsquod recommend also laying a layer of fibre-glass over the join By sanding or building up the strips you can adjust the amount offriction holding the centreboard
Layers of
HDF foam 25 mmpolyurethane
foam
Figure 27 Foam panels placed in between the sidewall panels
Ideally the centreboard should be a firm fit in the box otherwise when in the re-tracted position it has a tendency to flop back down particularly when bouncing over
18
Design and construction of a windsurfer longboard
Figure 28 Centre board box bottom view
pivot pin of centreboard
Deck
sidewall panel
friction strip
Figure 29 Friction strip which fits in the channel in the centreboard box
choppy waters Unless you are able to achieve high tolerances when manufacturingcentreboard box it is difficult to achieve a tight fit without having the centreboard jamwhen it is rotating It is better to leave some clearance in the centreboard box then packthe centreboard tight with what I call ldquofriction stripsrdquo These are simply strips about5 mm thick which are placed in the rebatted channel (shown in figure 26) after the cen-treboard is in place Initially I used plywood but found it wore out quickly so I endedup using sections from a sail batten built up to the required thickness with layers ofcarbon fibre and shown in figure 29 The strips are screwed down to the deck of theboard Make sure you place an adequate screw plug in the board Make the strips longenough so that they are in contact with the centreboard pivot pin figure 29
19
Chapter 3Mast track fin-box and footstrap plugs
When placing fittings into the board it is important to reinforce the board around thefitting using a higher density foam than the polystyrene core My approach was tobuild up a block of foam around each fitting I used 25 mm polyurethane 5 mm HDFand fibreglass to make sandwich panels that go around each part These panels helpspread the load and increase the top surface area of each part so there is more areafor the deck or hull lamination to adhere to I prepared all these parts before I startedbuilding the actual board This gave me practise in vacuum bagging on a small scale
31 Mast track
The part I had most difficulty getting was the sliding mast track I was quoted $200 fora mistral one-design track or $80 for a RSX track I opted for the RSX the only draw-back is that they donrsquot have as much travel as a traditional raceboard track figure 31Figure 32 shows the mast-track-box made out of high density foam The actual trackis screwed into the channel I used footstrap plugs as the anchor points for the screws
Figure 31 RSX mast track
32 Finbox and Footstrap plugs
I used a standard tuttle finbox You may wish to use a deep one instead but I believeformula style fins (or a fin gt 50 cm) are unnecessary for longboards so a standardshould do Foam sandwich panels are packed around the finbox and footstrap plugsto provide reinforcement figure 33
20
Design and construction of a windsurfer longboard
Figure 32 Mast track box made of urethaneHDFfibre sandwich
Figure 33 Finbox and footstrap plug reinforcements made of urethaneHDFfibresandwich
21
Chapter 4Board Construction
41 Shaping
The board is shaped as much as possible using a hotwire cutter Since the hotwire is astraight wire you cannot shaped doubly curved surfaces with it eg rails and deck forthese areas I shaped with sandpaper The sequence of shaping is as follows
1 hotwire cut rocker
2 hotwire cut vee
3 hotwire cut planshape
4 hotwire cut linear approximation of rail profile
5 hand sand deck and rail to required curve
The idea is to do as much shaping with a hotwire using templates to guide the cutEven when it came to fairing in the deck and rails I used cardboard templates of thecurve
411 Templates
I used A3 paper to print out templates of the centre-line profile (ie rocker) and plan-shape When creating these templates I subtracted the thickness of the HDF foam offthe template outline so that the specifications given earlier are for the built board notthe core To plot the profiles in full scale I used the vector graphics language AsymptoteSince an A3 piece of paper is 594times 420 mm I printed a section of the profile on eachpage then joined them all together These are the pdf files containing the templates
bull core-centre-linepdf
bull planshape-portpdf
bull planshape-starpdf 1
1Note the maximum half-width of the board is wider than an A3 sheet of paper so the planshape inthese files is referenced to a line offset 25 mm from the centre-line
22
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
Table 12 lists the actual costs of the materials that go into the board If you where tobuild in glass only you could probably get it down to $1300 There is excess HDF but2 sheets isnrsquot quite enough There is also the cost of consumables
bull paint brushes rollers
bull sandpaper
bull masking tape
bull gloves masks
bull material for templates
bull measuring beakers
I didnrsquot keep track of the cost of the consumables but itrsquos of the order $100 The othercosts include footstraps which for a the full 8 straps at $25 each would be $200 (luckilyI had some old ones I could use) and a fin $150 One thing I hadnrsquot factored in was theuniextension I tried to adapt an existing uni by replacing the pin to suit the rsx trackbut it seems the pin is unique to the rsx track so I could not source a suitable pin Inthe end I had to buy a new rsx mastfoot which was incompatible with my extensionstherefore a new extension too all up another $120
I have not included the cost of any tools I had to buy eg sur-form set-square andany of the electronics associated with the vacuum pump and hotwire
Table 12 Actual material costs in Australian dollars August 2008 For comparisonExocet Warp 380 raceboard $3500 Starboard formula $3150 Starboard Futura (freerideboard) $2500 or Neil Pryde X9 - 490cm mast $1600 For the complete board also factorin footstraps and fin and possibly the unimast extension These items take the costto around $2000 which is more than a Exocet Kona My point is you have to have acompelling reason to build it yourself other than cost
110 Time required to build
This was the most challenging aspect and I would advise anyone thinking of buildingto realistically consider whether they have the time available to complete the projectFor me the project changed from being enjoyable to a chore at about the 75 completemark When this happens you tend to start rushing and trying to take short cuts
I made the first hotwire cut on 29 September and applied the last coat of paint on8 November Prior to starting the board Irsquod made the centre board centre board boxmast track box and finbox reinforcement I worked on these bits and pieces over about6 months on and off Also factor in the time to make the templates The following isroughly how much time was spent on each step I estimate at least 100 hours of labourmaybe closer to 200 hours
Job When DaysBuilding the centreboard Sporadically 2-3 weekendsfittings amp templatesHotwire cutting and board shaping Weekend 2 full daysLaminating 80 done Week off work amp weekend 7 full daysFinal deck top lamination Weekend 1 full dayFilling the weave and sanding Weekend 2 part daysMore surface prep Week nights 1 day equivalentPainting amp fitting gaskets melb cup 4 day long weekend couple hrsdayMore painting Before and after work 1 day equivalentFinish painting Weekend 1 full day
14
Chapter 2Centreboard
21 Design of centreboard
The physics of the flow around an aerofoil is not trivial Motivated by the desire forefficient and fast flight a great deal of scientific and engineering research has beendevoted to the problem Methods for predicting the performance of aerofoils involveapproximations which are quite accurate at low angles of attack more challenging ispredicting the stall characteristics
In designing the centreboard there are two main aspects to consider
1 the aerofoil section which includes the maximum thickness of the aerofoil andpoint of maximum thickness
2 the plan shape
Since the centreboard is a symmetric aerofoil camber and twist are zero and the para-metric design space is somewhat reduced A considerable effort can be devoted to thedesign process However it is worth keeping in mind that hand shaping techniqueswill ultimately limit your ability to accurate produce it
211 Aerofoil section
Based on wind tunnel experiments a large database of aerofoil characteristics was com-plied in the 1930rsquos by NACA (National Advisory Committee of Aeronautics nowNASA) Figure 21 shows the what is referred to as the NACA0010 aerofoil sectionThe important parameter is the maximum thickness of this aerofoil which in this caseis 10 of the chord length c (hence the 10 in NACA0010 00 means no camber) Notethe chord is the straight line joining the leading edge to the trailing edge The numbersin figure 21 refer to selected x y (mm) coordinates on the upper surface relative to theorigin at the leading edge where in this example the chord c = 170 mm which is thechord length at the root of the aerofoil (ie at the point where the centreboard is againstthe hull) Left of the vertical red line is where I used the balsa wood moulding whichjust happened to fit the NACA0010 profile quite well The maximum thickness of theaerofoil is at x = 51 mm where y = t2 = 85 and hence t = 17 mm (ie 10 of c)where t is the thickness
Figure 21 The NACA0010 aerofoil section plotted for a chord length of 170 mm Thisfigure is to scale and can be used as a template if you print the page at 100 scale
Figure 22 Contour plot of what we want to achieve with hand tools and limited skillthis is a challenge
As will be seen in the next section we will choose an elliptic planform so that thechord length progressively reduces towards the tip of the centreboard This meanswe must continuously scale down the profile in figure 21 Figure 22 shows the sur-face contour of the centreboard required to achieve a NACA0010 section at all crosssections
212 Planshape
Mathematical analysis of wings is difficult However a classic result obtained in the1930rsquos is that for unswept wings an elliptical planform gives the minimum possibledrag for a given value of lift (ie it achieves the best LiftDrag ratio) So why notuse the elliptical planform if nothing else it looks better than a rectangular shapedcentreboard
22 Construction of centreboard
The centreboard is built using laminated cedar strips wrapped in a layer of carbonglassfibre using epoxy as the resin There are several useful articles on design and construc-tion of centreboard on the Internet (see for example Philrsquos Foils amp Composites MothHardware Phil Stevenson and Design and construction of centreboards and rudders PaulZander )
I used a rough-sawn cedar weather-board and ripped strips of around 35 mm wideSince I was cutting from a weather-board I could rip pieces of different thickness andbuild up a coarse approximation to the final aerofoil section The strips were gluedwith epoxy For the leading edge I used a piece of balsa around 12 mm wide whichwas pre-shaped into an aerofoil leading edge (try a model aircraft shop)
The centreboard is shaped using an electrical sander with coarse sandpaper I onlymade a template of the root sectional profile So at the end of this stage I had a rectan-
16
Design and construction of a windsurfer longboard
Figure 23 Cedar strips (approx 35 mm wide) and rounded balsa lead leading edge
Figure 24 After laminating a layer of carbonglass
gular planform with a constant sectional profile Next I cut the elliptic planform witha jigsaw The aerofoil section needs to be progressively thinned down towards the tip(ie trying to keep the ratio lc constant to achieve the contour of figure 22) To dothis accurately yoursquod need several sectional profiles for several different locations Inthe end I couldnrsquot be bothered with trying to accurately produce figure 22 and justthinned it out by eye Figure 23 shows the centreboard at this point low spots andimperfects have been filled (pink coloured epoxy filler)
After cutting the required shape of the area that goes through the board itrsquos readyto be laminated I used 200 gmminus2 carbon fibre double thickness from the handle toaround 50 mm below the root I ended up adding an extra layer of glass (130 gmminus2) asI thought Irsquod used too much resin and wanted to soak it up I did it all in one go andwrapped it in a vacuum bag and held it under vacuum overnight while it dried Thevacuum isnrsquot essential but does improve the result A photo of the centreboard afterremoving from the vacuum bag is shown in figure 24 the excess fibre on the trailingedge is easily trimmed off with a knife and sanded smooth donrsquot make it razor shape
23 Centreboard Box
The centreboard is highly loaded when working to windward Therefore it is necessaryto reinforce the board at the location of the centreboard I chose to build what I call acentreboard box which serves the same role as the fin box that is it provides structuralsupport for the lateral loading The difference between a fin box and centreboard boxapart from size is that the centreboard box must also provide a pivot point and asufficient cavity for the centreboard to fit in when in the retracted position The side
17
Design and construction of a windsurfer longboard
walls of the box are made of 25 mm thick polyurethane foam with 2 sheets of HDFlaminate onto the surface (between each layer of foam is 130 gmminus2 glass) To providea pivot point a 5 mm thick piece of marine ply is used with a channel cut into it Thispiece is plywood is recessed into the top HDF layer which also has a channel cut intoit Figure 25 shows the foam and plywood layup and figure 26 shows details of thepivot point prior to the final lamination The final lamination is made up of a layer of200gmminus2 carbon and a layer of 130 gmminus2 glass
180 mm
25 mm urethane foam
5 mm PVC5 mm plywood
1000 mm
Figure 25 Layup of sidewall panels for centreboard box
Figure 26 Plywood reinforcement provides support for centreboard pivot
The width of the centreboard box cavity is asymp 25 mm and chocks of foam 25 mmthick are glued in between the side wall panels At the front of the box I used a trian-gular shaped piece of HDF and at the rear I used polyurethane foam shaped to followthe shape of the trailing edge of the centreboard figure 27These chocks of foam werefirst laminated with fibreglass before gluing them in between the side panels Afterusing the board a few times I discovered a small leak at the rear of the box between thecentral piece of foam and the sidewalls so Irsquod recommend also laying a layer of fibre-glass over the join By sanding or building up the strips you can adjust the amount offriction holding the centreboard
Layers of
HDF foam 25 mmpolyurethane
foam
Figure 27 Foam panels placed in between the sidewall panels
Ideally the centreboard should be a firm fit in the box otherwise when in the re-tracted position it has a tendency to flop back down particularly when bouncing over
18
Design and construction of a windsurfer longboard
Figure 28 Centre board box bottom view
pivot pin of centreboard
Deck
sidewall panel
friction strip
Figure 29 Friction strip which fits in the channel in the centreboard box
choppy waters Unless you are able to achieve high tolerances when manufacturingcentreboard box it is difficult to achieve a tight fit without having the centreboard jamwhen it is rotating It is better to leave some clearance in the centreboard box then packthe centreboard tight with what I call ldquofriction stripsrdquo These are simply strips about5 mm thick which are placed in the rebatted channel (shown in figure 26) after the cen-treboard is in place Initially I used plywood but found it wore out quickly so I endedup using sections from a sail batten built up to the required thickness with layers ofcarbon fibre and shown in figure 29 The strips are screwed down to the deck of theboard Make sure you place an adequate screw plug in the board Make the strips longenough so that they are in contact with the centreboard pivot pin figure 29
19
Chapter 3Mast track fin-box and footstrap plugs
When placing fittings into the board it is important to reinforce the board around thefitting using a higher density foam than the polystyrene core My approach was tobuild up a block of foam around each fitting I used 25 mm polyurethane 5 mm HDFand fibreglass to make sandwich panels that go around each part These panels helpspread the load and increase the top surface area of each part so there is more areafor the deck or hull lamination to adhere to I prepared all these parts before I startedbuilding the actual board This gave me practise in vacuum bagging on a small scale
31 Mast track
The part I had most difficulty getting was the sliding mast track I was quoted $200 fora mistral one-design track or $80 for a RSX track I opted for the RSX the only draw-back is that they donrsquot have as much travel as a traditional raceboard track figure 31Figure 32 shows the mast-track-box made out of high density foam The actual trackis screwed into the channel I used footstrap plugs as the anchor points for the screws
Figure 31 RSX mast track
32 Finbox and Footstrap plugs
I used a standard tuttle finbox You may wish to use a deep one instead but I believeformula style fins (or a fin gt 50 cm) are unnecessary for longboards so a standardshould do Foam sandwich panels are packed around the finbox and footstrap plugsto provide reinforcement figure 33
20
Design and construction of a windsurfer longboard
Figure 32 Mast track box made of urethaneHDFfibre sandwich
Figure 33 Finbox and footstrap plug reinforcements made of urethaneHDFfibresandwich
21
Chapter 4Board Construction
41 Shaping
The board is shaped as much as possible using a hotwire cutter Since the hotwire is astraight wire you cannot shaped doubly curved surfaces with it eg rails and deck forthese areas I shaped with sandpaper The sequence of shaping is as follows
1 hotwire cut rocker
2 hotwire cut vee
3 hotwire cut planshape
4 hotwire cut linear approximation of rail profile
5 hand sand deck and rail to required curve
The idea is to do as much shaping with a hotwire using templates to guide the cutEven when it came to fairing in the deck and rails I used cardboard templates of thecurve
411 Templates
I used A3 paper to print out templates of the centre-line profile (ie rocker) and plan-shape When creating these templates I subtracted the thickness of the HDF foam offthe template outline so that the specifications given earlier are for the built board notthe core To plot the profiles in full scale I used the vector graphics language AsymptoteSince an A3 piece of paper is 594times 420 mm I printed a section of the profile on eachpage then joined them all together These are the pdf files containing the templates
bull core-centre-linepdf
bull planshape-portpdf
bull planshape-starpdf 1
1Note the maximum half-width of the board is wider than an A3 sheet of paper so the planshape inthese files is referenced to a line offset 25 mm from the centre-line
22
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
Table 12 Actual material costs in Australian dollars August 2008 For comparisonExocet Warp 380 raceboard $3500 Starboard formula $3150 Starboard Futura (freerideboard) $2500 or Neil Pryde X9 - 490cm mast $1600 For the complete board also factorin footstraps and fin and possibly the unimast extension These items take the costto around $2000 which is more than a Exocet Kona My point is you have to have acompelling reason to build it yourself other than cost
110 Time required to build
This was the most challenging aspect and I would advise anyone thinking of buildingto realistically consider whether they have the time available to complete the projectFor me the project changed from being enjoyable to a chore at about the 75 completemark When this happens you tend to start rushing and trying to take short cuts
I made the first hotwire cut on 29 September and applied the last coat of paint on8 November Prior to starting the board Irsquod made the centre board centre board boxmast track box and finbox reinforcement I worked on these bits and pieces over about6 months on and off Also factor in the time to make the templates The following isroughly how much time was spent on each step I estimate at least 100 hours of labourmaybe closer to 200 hours
Job When DaysBuilding the centreboard Sporadically 2-3 weekendsfittings amp templatesHotwire cutting and board shaping Weekend 2 full daysLaminating 80 done Week off work amp weekend 7 full daysFinal deck top lamination Weekend 1 full dayFilling the weave and sanding Weekend 2 part daysMore surface prep Week nights 1 day equivalentPainting amp fitting gaskets melb cup 4 day long weekend couple hrsdayMore painting Before and after work 1 day equivalentFinish painting Weekend 1 full day
14
Chapter 2Centreboard
21 Design of centreboard
The physics of the flow around an aerofoil is not trivial Motivated by the desire forefficient and fast flight a great deal of scientific and engineering research has beendevoted to the problem Methods for predicting the performance of aerofoils involveapproximations which are quite accurate at low angles of attack more challenging ispredicting the stall characteristics
In designing the centreboard there are two main aspects to consider
1 the aerofoil section which includes the maximum thickness of the aerofoil andpoint of maximum thickness
2 the plan shape
Since the centreboard is a symmetric aerofoil camber and twist are zero and the para-metric design space is somewhat reduced A considerable effort can be devoted to thedesign process However it is worth keeping in mind that hand shaping techniqueswill ultimately limit your ability to accurate produce it
211 Aerofoil section
Based on wind tunnel experiments a large database of aerofoil characteristics was com-plied in the 1930rsquos by NACA (National Advisory Committee of Aeronautics nowNASA) Figure 21 shows the what is referred to as the NACA0010 aerofoil sectionThe important parameter is the maximum thickness of this aerofoil which in this caseis 10 of the chord length c (hence the 10 in NACA0010 00 means no camber) Notethe chord is the straight line joining the leading edge to the trailing edge The numbersin figure 21 refer to selected x y (mm) coordinates on the upper surface relative to theorigin at the leading edge where in this example the chord c = 170 mm which is thechord length at the root of the aerofoil (ie at the point where the centreboard is againstthe hull) Left of the vertical red line is where I used the balsa wood moulding whichjust happened to fit the NACA0010 profile quite well The maximum thickness of theaerofoil is at x = 51 mm where y = t2 = 85 and hence t = 17 mm (ie 10 of c)where t is the thickness
Figure 21 The NACA0010 aerofoil section plotted for a chord length of 170 mm Thisfigure is to scale and can be used as a template if you print the page at 100 scale
Figure 22 Contour plot of what we want to achieve with hand tools and limited skillthis is a challenge
As will be seen in the next section we will choose an elliptic planform so that thechord length progressively reduces towards the tip of the centreboard This meanswe must continuously scale down the profile in figure 21 Figure 22 shows the sur-face contour of the centreboard required to achieve a NACA0010 section at all crosssections
212 Planshape
Mathematical analysis of wings is difficult However a classic result obtained in the1930rsquos is that for unswept wings an elliptical planform gives the minimum possibledrag for a given value of lift (ie it achieves the best LiftDrag ratio) So why notuse the elliptical planform if nothing else it looks better than a rectangular shapedcentreboard
22 Construction of centreboard
The centreboard is built using laminated cedar strips wrapped in a layer of carbonglassfibre using epoxy as the resin There are several useful articles on design and construc-tion of centreboard on the Internet (see for example Philrsquos Foils amp Composites MothHardware Phil Stevenson and Design and construction of centreboards and rudders PaulZander )
I used a rough-sawn cedar weather-board and ripped strips of around 35 mm wideSince I was cutting from a weather-board I could rip pieces of different thickness andbuild up a coarse approximation to the final aerofoil section The strips were gluedwith epoxy For the leading edge I used a piece of balsa around 12 mm wide whichwas pre-shaped into an aerofoil leading edge (try a model aircraft shop)
The centreboard is shaped using an electrical sander with coarse sandpaper I onlymade a template of the root sectional profile So at the end of this stage I had a rectan-
16
Design and construction of a windsurfer longboard
Figure 23 Cedar strips (approx 35 mm wide) and rounded balsa lead leading edge
Figure 24 After laminating a layer of carbonglass
gular planform with a constant sectional profile Next I cut the elliptic planform witha jigsaw The aerofoil section needs to be progressively thinned down towards the tip(ie trying to keep the ratio lc constant to achieve the contour of figure 22) To dothis accurately yoursquod need several sectional profiles for several different locations Inthe end I couldnrsquot be bothered with trying to accurately produce figure 22 and justthinned it out by eye Figure 23 shows the centreboard at this point low spots andimperfects have been filled (pink coloured epoxy filler)
After cutting the required shape of the area that goes through the board itrsquos readyto be laminated I used 200 gmminus2 carbon fibre double thickness from the handle toaround 50 mm below the root I ended up adding an extra layer of glass (130 gmminus2) asI thought Irsquod used too much resin and wanted to soak it up I did it all in one go andwrapped it in a vacuum bag and held it under vacuum overnight while it dried Thevacuum isnrsquot essential but does improve the result A photo of the centreboard afterremoving from the vacuum bag is shown in figure 24 the excess fibre on the trailingedge is easily trimmed off with a knife and sanded smooth donrsquot make it razor shape
23 Centreboard Box
The centreboard is highly loaded when working to windward Therefore it is necessaryto reinforce the board at the location of the centreboard I chose to build what I call acentreboard box which serves the same role as the fin box that is it provides structuralsupport for the lateral loading The difference between a fin box and centreboard boxapart from size is that the centreboard box must also provide a pivot point and asufficient cavity for the centreboard to fit in when in the retracted position The side
17
Design and construction of a windsurfer longboard
walls of the box are made of 25 mm thick polyurethane foam with 2 sheets of HDFlaminate onto the surface (between each layer of foam is 130 gmminus2 glass) To providea pivot point a 5 mm thick piece of marine ply is used with a channel cut into it Thispiece is plywood is recessed into the top HDF layer which also has a channel cut intoit Figure 25 shows the foam and plywood layup and figure 26 shows details of thepivot point prior to the final lamination The final lamination is made up of a layer of200gmminus2 carbon and a layer of 130 gmminus2 glass
180 mm
25 mm urethane foam
5 mm PVC5 mm plywood
1000 mm
Figure 25 Layup of sidewall panels for centreboard box
Figure 26 Plywood reinforcement provides support for centreboard pivot
The width of the centreboard box cavity is asymp 25 mm and chocks of foam 25 mmthick are glued in between the side wall panels At the front of the box I used a trian-gular shaped piece of HDF and at the rear I used polyurethane foam shaped to followthe shape of the trailing edge of the centreboard figure 27These chocks of foam werefirst laminated with fibreglass before gluing them in between the side panels Afterusing the board a few times I discovered a small leak at the rear of the box between thecentral piece of foam and the sidewalls so Irsquod recommend also laying a layer of fibre-glass over the join By sanding or building up the strips you can adjust the amount offriction holding the centreboard
Layers of
HDF foam 25 mmpolyurethane
foam
Figure 27 Foam panels placed in between the sidewall panels
Ideally the centreboard should be a firm fit in the box otherwise when in the re-tracted position it has a tendency to flop back down particularly when bouncing over
18
Design and construction of a windsurfer longboard
Figure 28 Centre board box bottom view
pivot pin of centreboard
Deck
sidewall panel
friction strip
Figure 29 Friction strip which fits in the channel in the centreboard box
choppy waters Unless you are able to achieve high tolerances when manufacturingcentreboard box it is difficult to achieve a tight fit without having the centreboard jamwhen it is rotating It is better to leave some clearance in the centreboard box then packthe centreboard tight with what I call ldquofriction stripsrdquo These are simply strips about5 mm thick which are placed in the rebatted channel (shown in figure 26) after the cen-treboard is in place Initially I used plywood but found it wore out quickly so I endedup using sections from a sail batten built up to the required thickness with layers ofcarbon fibre and shown in figure 29 The strips are screwed down to the deck of theboard Make sure you place an adequate screw plug in the board Make the strips longenough so that they are in contact with the centreboard pivot pin figure 29
19
Chapter 3Mast track fin-box and footstrap plugs
When placing fittings into the board it is important to reinforce the board around thefitting using a higher density foam than the polystyrene core My approach was tobuild up a block of foam around each fitting I used 25 mm polyurethane 5 mm HDFand fibreglass to make sandwich panels that go around each part These panels helpspread the load and increase the top surface area of each part so there is more areafor the deck or hull lamination to adhere to I prepared all these parts before I startedbuilding the actual board This gave me practise in vacuum bagging on a small scale
31 Mast track
The part I had most difficulty getting was the sliding mast track I was quoted $200 fora mistral one-design track or $80 for a RSX track I opted for the RSX the only draw-back is that they donrsquot have as much travel as a traditional raceboard track figure 31Figure 32 shows the mast-track-box made out of high density foam The actual trackis screwed into the channel I used footstrap plugs as the anchor points for the screws
Figure 31 RSX mast track
32 Finbox and Footstrap plugs
I used a standard tuttle finbox You may wish to use a deep one instead but I believeformula style fins (or a fin gt 50 cm) are unnecessary for longboards so a standardshould do Foam sandwich panels are packed around the finbox and footstrap plugsto provide reinforcement figure 33
20
Design and construction of a windsurfer longboard
Figure 32 Mast track box made of urethaneHDFfibre sandwich
Figure 33 Finbox and footstrap plug reinforcements made of urethaneHDFfibresandwich
21
Chapter 4Board Construction
41 Shaping
The board is shaped as much as possible using a hotwire cutter Since the hotwire is astraight wire you cannot shaped doubly curved surfaces with it eg rails and deck forthese areas I shaped with sandpaper The sequence of shaping is as follows
1 hotwire cut rocker
2 hotwire cut vee
3 hotwire cut planshape
4 hotwire cut linear approximation of rail profile
5 hand sand deck and rail to required curve
The idea is to do as much shaping with a hotwire using templates to guide the cutEven when it came to fairing in the deck and rails I used cardboard templates of thecurve
411 Templates
I used A3 paper to print out templates of the centre-line profile (ie rocker) and plan-shape When creating these templates I subtracted the thickness of the HDF foam offthe template outline so that the specifications given earlier are for the built board notthe core To plot the profiles in full scale I used the vector graphics language AsymptoteSince an A3 piece of paper is 594times 420 mm I printed a section of the profile on eachpage then joined them all together These are the pdf files containing the templates
bull core-centre-linepdf
bull planshape-portpdf
bull planshape-starpdf 1
1Note the maximum half-width of the board is wider than an A3 sheet of paper so the planshape inthese files is referenced to a line offset 25 mm from the centre-line
22
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Chapter 2Centreboard
21 Design of centreboard
The physics of the flow around an aerofoil is not trivial Motivated by the desire forefficient and fast flight a great deal of scientific and engineering research has beendevoted to the problem Methods for predicting the performance of aerofoils involveapproximations which are quite accurate at low angles of attack more challenging ispredicting the stall characteristics
In designing the centreboard there are two main aspects to consider
1 the aerofoil section which includes the maximum thickness of the aerofoil andpoint of maximum thickness
2 the plan shape
Since the centreboard is a symmetric aerofoil camber and twist are zero and the para-metric design space is somewhat reduced A considerable effort can be devoted to thedesign process However it is worth keeping in mind that hand shaping techniqueswill ultimately limit your ability to accurate produce it
211 Aerofoil section
Based on wind tunnel experiments a large database of aerofoil characteristics was com-plied in the 1930rsquos by NACA (National Advisory Committee of Aeronautics nowNASA) Figure 21 shows the what is referred to as the NACA0010 aerofoil sectionThe important parameter is the maximum thickness of this aerofoil which in this caseis 10 of the chord length c (hence the 10 in NACA0010 00 means no camber) Notethe chord is the straight line joining the leading edge to the trailing edge The numbersin figure 21 refer to selected x y (mm) coordinates on the upper surface relative to theorigin at the leading edge where in this example the chord c = 170 mm which is thechord length at the root of the aerofoil (ie at the point where the centreboard is againstthe hull) Left of the vertical red line is where I used the balsa wood moulding whichjust happened to fit the NACA0010 profile quite well The maximum thickness of theaerofoil is at x = 51 mm where y = t2 = 85 and hence t = 17 mm (ie 10 of c)where t is the thickness
Figure 21 The NACA0010 aerofoil section plotted for a chord length of 170 mm Thisfigure is to scale and can be used as a template if you print the page at 100 scale
Figure 22 Contour plot of what we want to achieve with hand tools and limited skillthis is a challenge
As will be seen in the next section we will choose an elliptic planform so that thechord length progressively reduces towards the tip of the centreboard This meanswe must continuously scale down the profile in figure 21 Figure 22 shows the sur-face contour of the centreboard required to achieve a NACA0010 section at all crosssections
212 Planshape
Mathematical analysis of wings is difficult However a classic result obtained in the1930rsquos is that for unswept wings an elliptical planform gives the minimum possibledrag for a given value of lift (ie it achieves the best LiftDrag ratio) So why notuse the elliptical planform if nothing else it looks better than a rectangular shapedcentreboard
22 Construction of centreboard
The centreboard is built using laminated cedar strips wrapped in a layer of carbonglassfibre using epoxy as the resin There are several useful articles on design and construc-tion of centreboard on the Internet (see for example Philrsquos Foils amp Composites MothHardware Phil Stevenson and Design and construction of centreboards and rudders PaulZander )
I used a rough-sawn cedar weather-board and ripped strips of around 35 mm wideSince I was cutting from a weather-board I could rip pieces of different thickness andbuild up a coarse approximation to the final aerofoil section The strips were gluedwith epoxy For the leading edge I used a piece of balsa around 12 mm wide whichwas pre-shaped into an aerofoil leading edge (try a model aircraft shop)
The centreboard is shaped using an electrical sander with coarse sandpaper I onlymade a template of the root sectional profile So at the end of this stage I had a rectan-
16
Design and construction of a windsurfer longboard
Figure 23 Cedar strips (approx 35 mm wide) and rounded balsa lead leading edge
Figure 24 After laminating a layer of carbonglass
gular planform with a constant sectional profile Next I cut the elliptic planform witha jigsaw The aerofoil section needs to be progressively thinned down towards the tip(ie trying to keep the ratio lc constant to achieve the contour of figure 22) To dothis accurately yoursquod need several sectional profiles for several different locations Inthe end I couldnrsquot be bothered with trying to accurately produce figure 22 and justthinned it out by eye Figure 23 shows the centreboard at this point low spots andimperfects have been filled (pink coloured epoxy filler)
After cutting the required shape of the area that goes through the board itrsquos readyto be laminated I used 200 gmminus2 carbon fibre double thickness from the handle toaround 50 mm below the root I ended up adding an extra layer of glass (130 gmminus2) asI thought Irsquod used too much resin and wanted to soak it up I did it all in one go andwrapped it in a vacuum bag and held it under vacuum overnight while it dried Thevacuum isnrsquot essential but does improve the result A photo of the centreboard afterremoving from the vacuum bag is shown in figure 24 the excess fibre on the trailingedge is easily trimmed off with a knife and sanded smooth donrsquot make it razor shape
23 Centreboard Box
The centreboard is highly loaded when working to windward Therefore it is necessaryto reinforce the board at the location of the centreboard I chose to build what I call acentreboard box which serves the same role as the fin box that is it provides structuralsupport for the lateral loading The difference between a fin box and centreboard boxapart from size is that the centreboard box must also provide a pivot point and asufficient cavity for the centreboard to fit in when in the retracted position The side
17
Design and construction of a windsurfer longboard
walls of the box are made of 25 mm thick polyurethane foam with 2 sheets of HDFlaminate onto the surface (between each layer of foam is 130 gmminus2 glass) To providea pivot point a 5 mm thick piece of marine ply is used with a channel cut into it Thispiece is plywood is recessed into the top HDF layer which also has a channel cut intoit Figure 25 shows the foam and plywood layup and figure 26 shows details of thepivot point prior to the final lamination The final lamination is made up of a layer of200gmminus2 carbon and a layer of 130 gmminus2 glass
180 mm
25 mm urethane foam
5 mm PVC5 mm plywood
1000 mm
Figure 25 Layup of sidewall panels for centreboard box
Figure 26 Plywood reinforcement provides support for centreboard pivot
The width of the centreboard box cavity is asymp 25 mm and chocks of foam 25 mmthick are glued in between the side wall panels At the front of the box I used a trian-gular shaped piece of HDF and at the rear I used polyurethane foam shaped to followthe shape of the trailing edge of the centreboard figure 27These chocks of foam werefirst laminated with fibreglass before gluing them in between the side panels Afterusing the board a few times I discovered a small leak at the rear of the box between thecentral piece of foam and the sidewalls so Irsquod recommend also laying a layer of fibre-glass over the join By sanding or building up the strips you can adjust the amount offriction holding the centreboard
Layers of
HDF foam 25 mmpolyurethane
foam
Figure 27 Foam panels placed in between the sidewall panels
Ideally the centreboard should be a firm fit in the box otherwise when in the re-tracted position it has a tendency to flop back down particularly when bouncing over
18
Design and construction of a windsurfer longboard
Figure 28 Centre board box bottom view
pivot pin of centreboard
Deck
sidewall panel
friction strip
Figure 29 Friction strip which fits in the channel in the centreboard box
choppy waters Unless you are able to achieve high tolerances when manufacturingcentreboard box it is difficult to achieve a tight fit without having the centreboard jamwhen it is rotating It is better to leave some clearance in the centreboard box then packthe centreboard tight with what I call ldquofriction stripsrdquo These are simply strips about5 mm thick which are placed in the rebatted channel (shown in figure 26) after the cen-treboard is in place Initially I used plywood but found it wore out quickly so I endedup using sections from a sail batten built up to the required thickness with layers ofcarbon fibre and shown in figure 29 The strips are screwed down to the deck of theboard Make sure you place an adequate screw plug in the board Make the strips longenough so that they are in contact with the centreboard pivot pin figure 29
19
Chapter 3Mast track fin-box and footstrap plugs
When placing fittings into the board it is important to reinforce the board around thefitting using a higher density foam than the polystyrene core My approach was tobuild up a block of foam around each fitting I used 25 mm polyurethane 5 mm HDFand fibreglass to make sandwich panels that go around each part These panels helpspread the load and increase the top surface area of each part so there is more areafor the deck or hull lamination to adhere to I prepared all these parts before I startedbuilding the actual board This gave me practise in vacuum bagging on a small scale
31 Mast track
The part I had most difficulty getting was the sliding mast track I was quoted $200 fora mistral one-design track or $80 for a RSX track I opted for the RSX the only draw-back is that they donrsquot have as much travel as a traditional raceboard track figure 31Figure 32 shows the mast-track-box made out of high density foam The actual trackis screwed into the channel I used footstrap plugs as the anchor points for the screws
Figure 31 RSX mast track
32 Finbox and Footstrap plugs
I used a standard tuttle finbox You may wish to use a deep one instead but I believeformula style fins (or a fin gt 50 cm) are unnecessary for longboards so a standardshould do Foam sandwich panels are packed around the finbox and footstrap plugsto provide reinforcement figure 33
20
Design and construction of a windsurfer longboard
Figure 32 Mast track box made of urethaneHDFfibre sandwich
Figure 33 Finbox and footstrap plug reinforcements made of urethaneHDFfibresandwich
21
Chapter 4Board Construction
41 Shaping
The board is shaped as much as possible using a hotwire cutter Since the hotwire is astraight wire you cannot shaped doubly curved surfaces with it eg rails and deck forthese areas I shaped with sandpaper The sequence of shaping is as follows
1 hotwire cut rocker
2 hotwire cut vee
3 hotwire cut planshape
4 hotwire cut linear approximation of rail profile
5 hand sand deck and rail to required curve
The idea is to do as much shaping with a hotwire using templates to guide the cutEven when it came to fairing in the deck and rails I used cardboard templates of thecurve
411 Templates
I used A3 paper to print out templates of the centre-line profile (ie rocker) and plan-shape When creating these templates I subtracted the thickness of the HDF foam offthe template outline so that the specifications given earlier are for the built board notthe core To plot the profiles in full scale I used the vector graphics language AsymptoteSince an A3 piece of paper is 594times 420 mm I printed a section of the profile on eachpage then joined them all together These are the pdf files containing the templates
bull core-centre-linepdf
bull planshape-portpdf
bull planshape-starpdf 1
1Note the maximum half-width of the board is wider than an A3 sheet of paper so the planshape inthese files is referenced to a line offset 25 mm from the centre-line
22
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
Figure 21 The NACA0010 aerofoil section plotted for a chord length of 170 mm Thisfigure is to scale and can be used as a template if you print the page at 100 scale
Figure 22 Contour plot of what we want to achieve with hand tools and limited skillthis is a challenge
As will be seen in the next section we will choose an elliptic planform so that thechord length progressively reduces towards the tip of the centreboard This meanswe must continuously scale down the profile in figure 21 Figure 22 shows the sur-face contour of the centreboard required to achieve a NACA0010 section at all crosssections
212 Planshape
Mathematical analysis of wings is difficult However a classic result obtained in the1930rsquos is that for unswept wings an elliptical planform gives the minimum possibledrag for a given value of lift (ie it achieves the best LiftDrag ratio) So why notuse the elliptical planform if nothing else it looks better than a rectangular shapedcentreboard
22 Construction of centreboard
The centreboard is built using laminated cedar strips wrapped in a layer of carbonglassfibre using epoxy as the resin There are several useful articles on design and construc-tion of centreboard on the Internet (see for example Philrsquos Foils amp Composites MothHardware Phil Stevenson and Design and construction of centreboards and rudders PaulZander )
I used a rough-sawn cedar weather-board and ripped strips of around 35 mm wideSince I was cutting from a weather-board I could rip pieces of different thickness andbuild up a coarse approximation to the final aerofoil section The strips were gluedwith epoxy For the leading edge I used a piece of balsa around 12 mm wide whichwas pre-shaped into an aerofoil leading edge (try a model aircraft shop)
The centreboard is shaped using an electrical sander with coarse sandpaper I onlymade a template of the root sectional profile So at the end of this stage I had a rectan-
16
Design and construction of a windsurfer longboard
Figure 23 Cedar strips (approx 35 mm wide) and rounded balsa lead leading edge
Figure 24 After laminating a layer of carbonglass
gular planform with a constant sectional profile Next I cut the elliptic planform witha jigsaw The aerofoil section needs to be progressively thinned down towards the tip(ie trying to keep the ratio lc constant to achieve the contour of figure 22) To dothis accurately yoursquod need several sectional profiles for several different locations Inthe end I couldnrsquot be bothered with trying to accurately produce figure 22 and justthinned it out by eye Figure 23 shows the centreboard at this point low spots andimperfects have been filled (pink coloured epoxy filler)
After cutting the required shape of the area that goes through the board itrsquos readyto be laminated I used 200 gmminus2 carbon fibre double thickness from the handle toaround 50 mm below the root I ended up adding an extra layer of glass (130 gmminus2) asI thought Irsquod used too much resin and wanted to soak it up I did it all in one go andwrapped it in a vacuum bag and held it under vacuum overnight while it dried Thevacuum isnrsquot essential but does improve the result A photo of the centreboard afterremoving from the vacuum bag is shown in figure 24 the excess fibre on the trailingedge is easily trimmed off with a knife and sanded smooth donrsquot make it razor shape
23 Centreboard Box
The centreboard is highly loaded when working to windward Therefore it is necessaryto reinforce the board at the location of the centreboard I chose to build what I call acentreboard box which serves the same role as the fin box that is it provides structuralsupport for the lateral loading The difference between a fin box and centreboard boxapart from size is that the centreboard box must also provide a pivot point and asufficient cavity for the centreboard to fit in when in the retracted position The side
17
Design and construction of a windsurfer longboard
walls of the box are made of 25 mm thick polyurethane foam with 2 sheets of HDFlaminate onto the surface (between each layer of foam is 130 gmminus2 glass) To providea pivot point a 5 mm thick piece of marine ply is used with a channel cut into it Thispiece is plywood is recessed into the top HDF layer which also has a channel cut intoit Figure 25 shows the foam and plywood layup and figure 26 shows details of thepivot point prior to the final lamination The final lamination is made up of a layer of200gmminus2 carbon and a layer of 130 gmminus2 glass
180 mm
25 mm urethane foam
5 mm PVC5 mm plywood
1000 mm
Figure 25 Layup of sidewall panels for centreboard box
Figure 26 Plywood reinforcement provides support for centreboard pivot
The width of the centreboard box cavity is asymp 25 mm and chocks of foam 25 mmthick are glued in between the side wall panels At the front of the box I used a trian-gular shaped piece of HDF and at the rear I used polyurethane foam shaped to followthe shape of the trailing edge of the centreboard figure 27These chocks of foam werefirst laminated with fibreglass before gluing them in between the side panels Afterusing the board a few times I discovered a small leak at the rear of the box between thecentral piece of foam and the sidewalls so Irsquod recommend also laying a layer of fibre-glass over the join By sanding or building up the strips you can adjust the amount offriction holding the centreboard
Layers of
HDF foam 25 mmpolyurethane
foam
Figure 27 Foam panels placed in between the sidewall panels
Ideally the centreboard should be a firm fit in the box otherwise when in the re-tracted position it has a tendency to flop back down particularly when bouncing over
18
Design and construction of a windsurfer longboard
Figure 28 Centre board box bottom view
pivot pin of centreboard
Deck
sidewall panel
friction strip
Figure 29 Friction strip which fits in the channel in the centreboard box
choppy waters Unless you are able to achieve high tolerances when manufacturingcentreboard box it is difficult to achieve a tight fit without having the centreboard jamwhen it is rotating It is better to leave some clearance in the centreboard box then packthe centreboard tight with what I call ldquofriction stripsrdquo These are simply strips about5 mm thick which are placed in the rebatted channel (shown in figure 26) after the cen-treboard is in place Initially I used plywood but found it wore out quickly so I endedup using sections from a sail batten built up to the required thickness with layers ofcarbon fibre and shown in figure 29 The strips are screwed down to the deck of theboard Make sure you place an adequate screw plug in the board Make the strips longenough so that they are in contact with the centreboard pivot pin figure 29
19
Chapter 3Mast track fin-box and footstrap plugs
When placing fittings into the board it is important to reinforce the board around thefitting using a higher density foam than the polystyrene core My approach was tobuild up a block of foam around each fitting I used 25 mm polyurethane 5 mm HDFand fibreglass to make sandwich panels that go around each part These panels helpspread the load and increase the top surface area of each part so there is more areafor the deck or hull lamination to adhere to I prepared all these parts before I startedbuilding the actual board This gave me practise in vacuum bagging on a small scale
31 Mast track
The part I had most difficulty getting was the sliding mast track I was quoted $200 fora mistral one-design track or $80 for a RSX track I opted for the RSX the only draw-back is that they donrsquot have as much travel as a traditional raceboard track figure 31Figure 32 shows the mast-track-box made out of high density foam The actual trackis screwed into the channel I used footstrap plugs as the anchor points for the screws
Figure 31 RSX mast track
32 Finbox and Footstrap plugs
I used a standard tuttle finbox You may wish to use a deep one instead but I believeformula style fins (or a fin gt 50 cm) are unnecessary for longboards so a standardshould do Foam sandwich panels are packed around the finbox and footstrap plugsto provide reinforcement figure 33
20
Design and construction of a windsurfer longboard
Figure 32 Mast track box made of urethaneHDFfibre sandwich
Figure 33 Finbox and footstrap plug reinforcements made of urethaneHDFfibresandwich
21
Chapter 4Board Construction
41 Shaping
The board is shaped as much as possible using a hotwire cutter Since the hotwire is astraight wire you cannot shaped doubly curved surfaces with it eg rails and deck forthese areas I shaped with sandpaper The sequence of shaping is as follows
1 hotwire cut rocker
2 hotwire cut vee
3 hotwire cut planshape
4 hotwire cut linear approximation of rail profile
5 hand sand deck and rail to required curve
The idea is to do as much shaping with a hotwire using templates to guide the cutEven when it came to fairing in the deck and rails I used cardboard templates of thecurve
411 Templates
I used A3 paper to print out templates of the centre-line profile (ie rocker) and plan-shape When creating these templates I subtracted the thickness of the HDF foam offthe template outline so that the specifications given earlier are for the built board notthe core To plot the profiles in full scale I used the vector graphics language AsymptoteSince an A3 piece of paper is 594times 420 mm I printed a section of the profile on eachpage then joined them all together These are the pdf files containing the templates
bull core-centre-linepdf
bull planshape-portpdf
bull planshape-starpdf 1
1Note the maximum half-width of the board is wider than an A3 sheet of paper so the planshape inthese files is referenced to a line offset 25 mm from the centre-line
22
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
Figure 23 Cedar strips (approx 35 mm wide) and rounded balsa lead leading edge
Figure 24 After laminating a layer of carbonglass
gular planform with a constant sectional profile Next I cut the elliptic planform witha jigsaw The aerofoil section needs to be progressively thinned down towards the tip(ie trying to keep the ratio lc constant to achieve the contour of figure 22) To dothis accurately yoursquod need several sectional profiles for several different locations Inthe end I couldnrsquot be bothered with trying to accurately produce figure 22 and justthinned it out by eye Figure 23 shows the centreboard at this point low spots andimperfects have been filled (pink coloured epoxy filler)
After cutting the required shape of the area that goes through the board itrsquos readyto be laminated I used 200 gmminus2 carbon fibre double thickness from the handle toaround 50 mm below the root I ended up adding an extra layer of glass (130 gmminus2) asI thought Irsquod used too much resin and wanted to soak it up I did it all in one go andwrapped it in a vacuum bag and held it under vacuum overnight while it dried Thevacuum isnrsquot essential but does improve the result A photo of the centreboard afterremoving from the vacuum bag is shown in figure 24 the excess fibre on the trailingedge is easily trimmed off with a knife and sanded smooth donrsquot make it razor shape
23 Centreboard Box
The centreboard is highly loaded when working to windward Therefore it is necessaryto reinforce the board at the location of the centreboard I chose to build what I call acentreboard box which serves the same role as the fin box that is it provides structuralsupport for the lateral loading The difference between a fin box and centreboard boxapart from size is that the centreboard box must also provide a pivot point and asufficient cavity for the centreboard to fit in when in the retracted position The side
17
Design and construction of a windsurfer longboard
walls of the box are made of 25 mm thick polyurethane foam with 2 sheets of HDFlaminate onto the surface (between each layer of foam is 130 gmminus2 glass) To providea pivot point a 5 mm thick piece of marine ply is used with a channel cut into it Thispiece is plywood is recessed into the top HDF layer which also has a channel cut intoit Figure 25 shows the foam and plywood layup and figure 26 shows details of thepivot point prior to the final lamination The final lamination is made up of a layer of200gmminus2 carbon and a layer of 130 gmminus2 glass
180 mm
25 mm urethane foam
5 mm PVC5 mm plywood
1000 mm
Figure 25 Layup of sidewall panels for centreboard box
Figure 26 Plywood reinforcement provides support for centreboard pivot
The width of the centreboard box cavity is asymp 25 mm and chocks of foam 25 mmthick are glued in between the side wall panels At the front of the box I used a trian-gular shaped piece of HDF and at the rear I used polyurethane foam shaped to followthe shape of the trailing edge of the centreboard figure 27These chocks of foam werefirst laminated with fibreglass before gluing them in between the side panels Afterusing the board a few times I discovered a small leak at the rear of the box between thecentral piece of foam and the sidewalls so Irsquod recommend also laying a layer of fibre-glass over the join By sanding or building up the strips you can adjust the amount offriction holding the centreboard
Layers of
HDF foam 25 mmpolyurethane
foam
Figure 27 Foam panels placed in between the sidewall panels
Ideally the centreboard should be a firm fit in the box otherwise when in the re-tracted position it has a tendency to flop back down particularly when bouncing over
18
Design and construction of a windsurfer longboard
Figure 28 Centre board box bottom view
pivot pin of centreboard
Deck
sidewall panel
friction strip
Figure 29 Friction strip which fits in the channel in the centreboard box
choppy waters Unless you are able to achieve high tolerances when manufacturingcentreboard box it is difficult to achieve a tight fit without having the centreboard jamwhen it is rotating It is better to leave some clearance in the centreboard box then packthe centreboard tight with what I call ldquofriction stripsrdquo These are simply strips about5 mm thick which are placed in the rebatted channel (shown in figure 26) after the cen-treboard is in place Initially I used plywood but found it wore out quickly so I endedup using sections from a sail batten built up to the required thickness with layers ofcarbon fibre and shown in figure 29 The strips are screwed down to the deck of theboard Make sure you place an adequate screw plug in the board Make the strips longenough so that they are in contact with the centreboard pivot pin figure 29
19
Chapter 3Mast track fin-box and footstrap plugs
When placing fittings into the board it is important to reinforce the board around thefitting using a higher density foam than the polystyrene core My approach was tobuild up a block of foam around each fitting I used 25 mm polyurethane 5 mm HDFand fibreglass to make sandwich panels that go around each part These panels helpspread the load and increase the top surface area of each part so there is more areafor the deck or hull lamination to adhere to I prepared all these parts before I startedbuilding the actual board This gave me practise in vacuum bagging on a small scale
31 Mast track
The part I had most difficulty getting was the sliding mast track I was quoted $200 fora mistral one-design track or $80 for a RSX track I opted for the RSX the only draw-back is that they donrsquot have as much travel as a traditional raceboard track figure 31Figure 32 shows the mast-track-box made out of high density foam The actual trackis screwed into the channel I used footstrap plugs as the anchor points for the screws
Figure 31 RSX mast track
32 Finbox and Footstrap plugs
I used a standard tuttle finbox You may wish to use a deep one instead but I believeformula style fins (or a fin gt 50 cm) are unnecessary for longboards so a standardshould do Foam sandwich panels are packed around the finbox and footstrap plugsto provide reinforcement figure 33
20
Design and construction of a windsurfer longboard
Figure 32 Mast track box made of urethaneHDFfibre sandwich
Figure 33 Finbox and footstrap plug reinforcements made of urethaneHDFfibresandwich
21
Chapter 4Board Construction
41 Shaping
The board is shaped as much as possible using a hotwire cutter Since the hotwire is astraight wire you cannot shaped doubly curved surfaces with it eg rails and deck forthese areas I shaped with sandpaper The sequence of shaping is as follows
1 hotwire cut rocker
2 hotwire cut vee
3 hotwire cut planshape
4 hotwire cut linear approximation of rail profile
5 hand sand deck and rail to required curve
The idea is to do as much shaping with a hotwire using templates to guide the cutEven when it came to fairing in the deck and rails I used cardboard templates of thecurve
411 Templates
I used A3 paper to print out templates of the centre-line profile (ie rocker) and plan-shape When creating these templates I subtracted the thickness of the HDF foam offthe template outline so that the specifications given earlier are for the built board notthe core To plot the profiles in full scale I used the vector graphics language AsymptoteSince an A3 piece of paper is 594times 420 mm I printed a section of the profile on eachpage then joined them all together These are the pdf files containing the templates
bull core-centre-linepdf
bull planshape-portpdf
bull planshape-starpdf 1
1Note the maximum half-width of the board is wider than an A3 sheet of paper so the planshape inthese files is referenced to a line offset 25 mm from the centre-line
22
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
walls of the box are made of 25 mm thick polyurethane foam with 2 sheets of HDFlaminate onto the surface (between each layer of foam is 130 gmminus2 glass) To providea pivot point a 5 mm thick piece of marine ply is used with a channel cut into it Thispiece is plywood is recessed into the top HDF layer which also has a channel cut intoit Figure 25 shows the foam and plywood layup and figure 26 shows details of thepivot point prior to the final lamination The final lamination is made up of a layer of200gmminus2 carbon and a layer of 130 gmminus2 glass
180 mm
25 mm urethane foam
5 mm PVC5 mm plywood
1000 mm
Figure 25 Layup of sidewall panels for centreboard box
Figure 26 Plywood reinforcement provides support for centreboard pivot
The width of the centreboard box cavity is asymp 25 mm and chocks of foam 25 mmthick are glued in between the side wall panels At the front of the box I used a trian-gular shaped piece of HDF and at the rear I used polyurethane foam shaped to followthe shape of the trailing edge of the centreboard figure 27These chocks of foam werefirst laminated with fibreglass before gluing them in between the side panels Afterusing the board a few times I discovered a small leak at the rear of the box between thecentral piece of foam and the sidewalls so Irsquod recommend also laying a layer of fibre-glass over the join By sanding or building up the strips you can adjust the amount offriction holding the centreboard
Layers of
HDF foam 25 mmpolyurethane
foam
Figure 27 Foam panels placed in between the sidewall panels
Ideally the centreboard should be a firm fit in the box otherwise when in the re-tracted position it has a tendency to flop back down particularly when bouncing over
18
Design and construction of a windsurfer longboard
Figure 28 Centre board box bottom view
pivot pin of centreboard
Deck
sidewall panel
friction strip
Figure 29 Friction strip which fits in the channel in the centreboard box
choppy waters Unless you are able to achieve high tolerances when manufacturingcentreboard box it is difficult to achieve a tight fit without having the centreboard jamwhen it is rotating It is better to leave some clearance in the centreboard box then packthe centreboard tight with what I call ldquofriction stripsrdquo These are simply strips about5 mm thick which are placed in the rebatted channel (shown in figure 26) after the cen-treboard is in place Initially I used plywood but found it wore out quickly so I endedup using sections from a sail batten built up to the required thickness with layers ofcarbon fibre and shown in figure 29 The strips are screwed down to the deck of theboard Make sure you place an adequate screw plug in the board Make the strips longenough so that they are in contact with the centreboard pivot pin figure 29
19
Chapter 3Mast track fin-box and footstrap plugs
When placing fittings into the board it is important to reinforce the board around thefitting using a higher density foam than the polystyrene core My approach was tobuild up a block of foam around each fitting I used 25 mm polyurethane 5 mm HDFand fibreglass to make sandwich panels that go around each part These panels helpspread the load and increase the top surface area of each part so there is more areafor the deck or hull lamination to adhere to I prepared all these parts before I startedbuilding the actual board This gave me practise in vacuum bagging on a small scale
31 Mast track
The part I had most difficulty getting was the sliding mast track I was quoted $200 fora mistral one-design track or $80 for a RSX track I opted for the RSX the only draw-back is that they donrsquot have as much travel as a traditional raceboard track figure 31Figure 32 shows the mast-track-box made out of high density foam The actual trackis screwed into the channel I used footstrap plugs as the anchor points for the screws
Figure 31 RSX mast track
32 Finbox and Footstrap plugs
I used a standard tuttle finbox You may wish to use a deep one instead but I believeformula style fins (or a fin gt 50 cm) are unnecessary for longboards so a standardshould do Foam sandwich panels are packed around the finbox and footstrap plugsto provide reinforcement figure 33
20
Design and construction of a windsurfer longboard
Figure 32 Mast track box made of urethaneHDFfibre sandwich
Figure 33 Finbox and footstrap plug reinforcements made of urethaneHDFfibresandwich
21
Chapter 4Board Construction
41 Shaping
The board is shaped as much as possible using a hotwire cutter Since the hotwire is astraight wire you cannot shaped doubly curved surfaces with it eg rails and deck forthese areas I shaped with sandpaper The sequence of shaping is as follows
1 hotwire cut rocker
2 hotwire cut vee
3 hotwire cut planshape
4 hotwire cut linear approximation of rail profile
5 hand sand deck and rail to required curve
The idea is to do as much shaping with a hotwire using templates to guide the cutEven when it came to fairing in the deck and rails I used cardboard templates of thecurve
411 Templates
I used A3 paper to print out templates of the centre-line profile (ie rocker) and plan-shape When creating these templates I subtracted the thickness of the HDF foam offthe template outline so that the specifications given earlier are for the built board notthe core To plot the profiles in full scale I used the vector graphics language AsymptoteSince an A3 piece of paper is 594times 420 mm I printed a section of the profile on eachpage then joined them all together These are the pdf files containing the templates
bull core-centre-linepdf
bull planshape-portpdf
bull planshape-starpdf 1
1Note the maximum half-width of the board is wider than an A3 sheet of paper so the planshape inthese files is referenced to a line offset 25 mm from the centre-line
22
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
Figure 28 Centre board box bottom view
pivot pin of centreboard
Deck
sidewall panel
friction strip
Figure 29 Friction strip which fits in the channel in the centreboard box
choppy waters Unless you are able to achieve high tolerances when manufacturingcentreboard box it is difficult to achieve a tight fit without having the centreboard jamwhen it is rotating It is better to leave some clearance in the centreboard box then packthe centreboard tight with what I call ldquofriction stripsrdquo These are simply strips about5 mm thick which are placed in the rebatted channel (shown in figure 26) after the cen-treboard is in place Initially I used plywood but found it wore out quickly so I endedup using sections from a sail batten built up to the required thickness with layers ofcarbon fibre and shown in figure 29 The strips are screwed down to the deck of theboard Make sure you place an adequate screw plug in the board Make the strips longenough so that they are in contact with the centreboard pivot pin figure 29
19
Chapter 3Mast track fin-box and footstrap plugs
When placing fittings into the board it is important to reinforce the board around thefitting using a higher density foam than the polystyrene core My approach was tobuild up a block of foam around each fitting I used 25 mm polyurethane 5 mm HDFand fibreglass to make sandwich panels that go around each part These panels helpspread the load and increase the top surface area of each part so there is more areafor the deck or hull lamination to adhere to I prepared all these parts before I startedbuilding the actual board This gave me practise in vacuum bagging on a small scale
31 Mast track
The part I had most difficulty getting was the sliding mast track I was quoted $200 fora mistral one-design track or $80 for a RSX track I opted for the RSX the only draw-back is that they donrsquot have as much travel as a traditional raceboard track figure 31Figure 32 shows the mast-track-box made out of high density foam The actual trackis screwed into the channel I used footstrap plugs as the anchor points for the screws
Figure 31 RSX mast track
32 Finbox and Footstrap plugs
I used a standard tuttle finbox You may wish to use a deep one instead but I believeformula style fins (or a fin gt 50 cm) are unnecessary for longboards so a standardshould do Foam sandwich panels are packed around the finbox and footstrap plugsto provide reinforcement figure 33
20
Design and construction of a windsurfer longboard
Figure 32 Mast track box made of urethaneHDFfibre sandwich
Figure 33 Finbox and footstrap plug reinforcements made of urethaneHDFfibresandwich
21
Chapter 4Board Construction
41 Shaping
The board is shaped as much as possible using a hotwire cutter Since the hotwire is astraight wire you cannot shaped doubly curved surfaces with it eg rails and deck forthese areas I shaped with sandpaper The sequence of shaping is as follows
1 hotwire cut rocker
2 hotwire cut vee
3 hotwire cut planshape
4 hotwire cut linear approximation of rail profile
5 hand sand deck and rail to required curve
The idea is to do as much shaping with a hotwire using templates to guide the cutEven when it came to fairing in the deck and rails I used cardboard templates of thecurve
411 Templates
I used A3 paper to print out templates of the centre-line profile (ie rocker) and plan-shape When creating these templates I subtracted the thickness of the HDF foam offthe template outline so that the specifications given earlier are for the built board notthe core To plot the profiles in full scale I used the vector graphics language AsymptoteSince an A3 piece of paper is 594times 420 mm I printed a section of the profile on eachpage then joined them all together These are the pdf files containing the templates
bull core-centre-linepdf
bull planshape-portpdf
bull planshape-starpdf 1
1Note the maximum half-width of the board is wider than an A3 sheet of paper so the planshape inthese files is referenced to a line offset 25 mm from the centre-line
22
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Chapter 3Mast track fin-box and footstrap plugs
When placing fittings into the board it is important to reinforce the board around thefitting using a higher density foam than the polystyrene core My approach was tobuild up a block of foam around each fitting I used 25 mm polyurethane 5 mm HDFand fibreglass to make sandwich panels that go around each part These panels helpspread the load and increase the top surface area of each part so there is more areafor the deck or hull lamination to adhere to I prepared all these parts before I startedbuilding the actual board This gave me practise in vacuum bagging on a small scale
31 Mast track
The part I had most difficulty getting was the sliding mast track I was quoted $200 fora mistral one-design track or $80 for a RSX track I opted for the RSX the only draw-back is that they donrsquot have as much travel as a traditional raceboard track figure 31Figure 32 shows the mast-track-box made out of high density foam The actual trackis screwed into the channel I used footstrap plugs as the anchor points for the screws
Figure 31 RSX mast track
32 Finbox and Footstrap plugs
I used a standard tuttle finbox You may wish to use a deep one instead but I believeformula style fins (or a fin gt 50 cm) are unnecessary for longboards so a standardshould do Foam sandwich panels are packed around the finbox and footstrap plugsto provide reinforcement figure 33
20
Design and construction of a windsurfer longboard
Figure 32 Mast track box made of urethaneHDFfibre sandwich
Figure 33 Finbox and footstrap plug reinforcements made of urethaneHDFfibresandwich
21
Chapter 4Board Construction
41 Shaping
The board is shaped as much as possible using a hotwire cutter Since the hotwire is astraight wire you cannot shaped doubly curved surfaces with it eg rails and deck forthese areas I shaped with sandpaper The sequence of shaping is as follows
1 hotwire cut rocker
2 hotwire cut vee
3 hotwire cut planshape
4 hotwire cut linear approximation of rail profile
5 hand sand deck and rail to required curve
The idea is to do as much shaping with a hotwire using templates to guide the cutEven when it came to fairing in the deck and rails I used cardboard templates of thecurve
411 Templates
I used A3 paper to print out templates of the centre-line profile (ie rocker) and plan-shape When creating these templates I subtracted the thickness of the HDF foam offthe template outline so that the specifications given earlier are for the built board notthe core To plot the profiles in full scale I used the vector graphics language AsymptoteSince an A3 piece of paper is 594times 420 mm I printed a section of the profile on eachpage then joined them all together These are the pdf files containing the templates
bull core-centre-linepdf
bull planshape-portpdf
bull planshape-starpdf 1
1Note the maximum half-width of the board is wider than an A3 sheet of paper so the planshape inthese files is referenced to a line offset 25 mm from the centre-line
22
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
Figure 32 Mast track box made of urethaneHDFfibre sandwich
Figure 33 Finbox and footstrap plug reinforcements made of urethaneHDFfibresandwich
21
Chapter 4Board Construction
41 Shaping
The board is shaped as much as possible using a hotwire cutter Since the hotwire is astraight wire you cannot shaped doubly curved surfaces with it eg rails and deck forthese areas I shaped with sandpaper The sequence of shaping is as follows
1 hotwire cut rocker
2 hotwire cut vee
3 hotwire cut planshape
4 hotwire cut linear approximation of rail profile
5 hand sand deck and rail to required curve
The idea is to do as much shaping with a hotwire using templates to guide the cutEven when it came to fairing in the deck and rails I used cardboard templates of thecurve
411 Templates
I used A3 paper to print out templates of the centre-line profile (ie rocker) and plan-shape When creating these templates I subtracted the thickness of the HDF foam offthe template outline so that the specifications given earlier are for the built board notthe core To plot the profiles in full scale I used the vector graphics language AsymptoteSince an A3 piece of paper is 594times 420 mm I printed a section of the profile on eachpage then joined them all together These are the pdf files containing the templates
bull core-centre-linepdf
bull planshape-portpdf
bull planshape-starpdf 1
1Note the maximum half-width of the board is wider than an A3 sheet of paper so the planshape inthese files is referenced to a line offset 25 mm from the centre-line
22
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Chapter 4Board Construction
41 Shaping
The board is shaped as much as possible using a hotwire cutter Since the hotwire is astraight wire you cannot shaped doubly curved surfaces with it eg rails and deck forthese areas I shaped with sandpaper The sequence of shaping is as follows
1 hotwire cut rocker
2 hotwire cut vee
3 hotwire cut planshape
4 hotwire cut linear approximation of rail profile
5 hand sand deck and rail to required curve
The idea is to do as much shaping with a hotwire using templates to guide the cutEven when it came to fairing in the deck and rails I used cardboard templates of thecurve
411 Templates
I used A3 paper to print out templates of the centre-line profile (ie rocker) and plan-shape When creating these templates I subtracted the thickness of the HDF foam offthe template outline so that the specifications given earlier are for the built board notthe core To plot the profiles in full scale I used the vector graphics language AsymptoteSince an A3 piece of paper is 594times 420 mm I printed a section of the profile on eachpage then joined them all together These are the pdf files containing the templates
bull core-centre-linepdf
bull planshape-portpdf
bull planshape-starpdf 1
1Note the maximum half-width of the board is wider than an A3 sheet of paper so the planshape inthese files is referenced to a line offset 25 mm from the centre-line
22
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = (0 0)
page 1
Last point = ( 420 117893)
First point bottom = (0 0)
Last point = ( 420 5)
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = (0 117893)
page 2
Last point = ( 840 163073)
First point bottom = (0 5)
Last point = ( 840 500001)
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = (0 163073)
page 3
Last point = ( 1260 174916)
First point bottom = (0 500001)
Last point = ( 1260 514947)
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = (0 174916)
page 4
Last point = ( 1680 174989)
First point bottom = (0 5159)
Last point = ( 1680 699921)
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = (0 174989)
page 5
Last point = ( 2100 175291)
First point bottom = (0 708601)
Last point = ( 2100 145155)
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = (0 175291)
page 6
Last point = ( 2520 177722)
First point bottom = (0 148613)
Last point = ( 2520 341412)
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = (0 177722)
page 7
Last point = ( 2940 191128)
First point bottom = (0 351005)
Last point = ( 2940 747865)
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = (0 191128)
page 8
Last point = ( 3360 224345)
First point bottom = (0 749597)
Last point = ( 3360 147811)
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = (0 224345)
page 9
Last point = ( 3780 28293)
First point bottom = (0 148677)
Last point = ( 3780 26702)
Rocker and deck profile
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = ( 29788-0356011)
page 1
Last point = ( 4202 198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = ( 4202 198446)
page 2
Last point = ( 8404 267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = ( 8404 267607)
page 3
Last point = ( 12606 306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = ( 12606 306569)
page 4
Last point = ( 16808 316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = ( 16808 316235)
page 5
Last point = ( 2101 316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = ( 2101 316938)
page 6
Last point = ( 25212 30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = ( 25212 30949)
page 7
Last point = ( 29414 28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = ( 29414 28168)
page 8
Last point = ( 33616 213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = ( 33616 213866)
page 9
Last point = ( 37818 15011)
Port planshape
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = ( 29788-0356011)
page 1
Last point = ( 4202-198446)
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = ( 4202 198446)
page 2
Last point = ( 8404-267607)
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = ( 8404 267607)
page 3
Last point = ( 12606-306569)
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = ( 12606 306569)
page 4
Last point = ( 16808-316235)
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = ( 16808 316235)
page 5
Last point = ( 2101-316938)
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = ( 2101 316938)
page 6
Last point = ( 25212 -30949)
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = ( 25212 30949)
page 7
Last point = ( 29414 -28168)
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = ( 29414 28168)
page 8
Last point = ( 33616-213866)
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
First point = ( 33616 213866)
page 9
Last point = ( 37818 -15011)
Starboard planshape
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
412 Core
The core is made of polystyrene I used two blocks measuring 20times 06times 03 m fig-ure 41 Polystyrene is available in two forms expanded or extruded The lightest butweakest is expanded which comes in different densities from around 12minus 14 kgmminus3
upwards First I glued them together using liquid nails make sure the glue stayswithin the cutting path of the hotwire Note I could have bought the block as onepiece but did not have a vehicle to transport such a long block in I wouldnrsquot risk iton a roof rack Check the squareness of the block and take this into account whenattaching the templates
413 Rocker and deck
The rockerdeck centre-line profile is transferred to a two pieces of MDF (mediumdensity fibre) These templates are aligned and then screwed into the sides of thefoam block I did the deck cut first then flipped the board and cut the rocker profileFigure 42 shows the core after the rocker and deck centre-line profile has been cut
414 Vee
The design has 1o of vee along the full length of the board For a block 700 mm widethis equates to a drop off of 350times tan(1o) = 6 mm at the edge of the block Thereforeone rocker template is lowered by 6 mm To provide a guide on the other side theopposite template is raised by 6 mm Note when you do the 2nd vee cut you need toraise the opposite side 2times 6 = 12 mm relative to its edge To make sure the wire doesnot cross the centre line I placed a strip of masking tape along the boardrsquos centre-line(see figure 42)
415 Planshape
I used cardboard for the planshape templates These are taped and pinned to the topand bottom of the board again alignment is important The hotwire cutter is then usedto cut the planshape Actually I did this cut by myself but even though the width ofthe cut is smaller than for the rocker and vee itrsquos still difficult to keep an eye on bothtemplates and there is a tendency to lift off every so often You end up with a humpwhich is easily sanded back but for a perfect cut 2 people are best Figure 43 showsthe core so far
416 Rails
The curve of the deck and rails can be rough cut by making a series of hotwire cutsFigure 44 shows how a series of 4 hotwire cuts achieves a profile close to the requiredcurve Actually in retrospect I would not attempt the fourth cut since it is too shallowUse masking tape to provide the guide for the hotwire Obviously the cross sectionprofile varies along the length of the board so this technique is applied to a section at atime Starting at the widest point of the board and working towards the tips Alwaysmake sure the hotwire cuts are on or outside of the final profile since you want to sand
23
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
Figure 41 4 m of polystyrene Was this such a good idea
down to the desired shape rather than filling back up Actually in retrospect it wouldbe better to have stuck the tape guides along the entire length of the board rather thandoing a section at a time and do one long continuous hotwire cut rather than sectionsIn figure 45 I have made the first cut at the mid section of the board
Once the rough cutting is done it is all faired in by sanding For the mid-sectionsof the board there is very little variation in the cross sectional profile so one templatecovers most of the length here Toward the nose and tail a greater number of templatesare required These templates are used to guide the fairing of the rail and deck whichis done by hand with sandpaper The exact cross section profiles that are required areshown in figures 14 and 15 Figure 47 shows the final shaped core I still have a bitof fine shaping Unfortunately there are a few low spots on the deckrail area that stillneed attention these occurred due to the section-by-section approach I took If I wasto do it again Irsquod do continuous rail cuts Fortunately the hull which is the criticalgeometry is the easiest to shape So small deck imperfections are more cosmetic (notelarger imperfections will cause bridging of the HDF and sites for delimitation)
42 Laminating
The lamination schedule is as follows
1 laminate carbonHDF (5 mm) to bottom
2 laminate carbonHDF (5 mm) to deck
3 glue in all fittings
4 laminate glassHDF (3 mm) to rails
5 laminate carbon to bottom
6 laminate carbon to deck and rails
24
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
Figure 42 Foam core after cutting the rocker blue tape marks centre-line and assist inguiding the hotwire for the vee cut to follow
Figure 43 After cutting the planshape
25
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
polystyrene block
hotwire cutsrequired profile
linear approx
First cut
Last cutuse masking tape to guide
the cuts
Figure 44 The rail and deck is rough shaped by making a series of straight cuts Thefoam is then faired to the required profile using sandpaper and templates The circlesin the figure show where the tape edge is placed for each cut To determine the positionI printed full scale cross sections drew on the cuts and then measured the location ofthese points
Figure 45 After make the first hotwire cut for the mid-section rail
Figure 46 Shaped mid-rails instead work the entire rail in one go not section bysection
26
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
Figure 47 The bulk of the shaping done just have to remove imperfections
27
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
carbon fibre 200 gmminus2
Polystyrene core
5 mm HDF (Klegecell 80 gmminus3)
Figure 48 Layup used on both deck and hull on the rails 3 mm HDF is used
Figure 48 shows the general layup used although extra reinforcement patches are usedaround all fittings These are the make it or break it steps Whereas in the shaping stagethings may not quite turn out as planned it is hard to totally stuff it up no so with thelaminating Epoxy has a working time of around 1 hr so while the laminating is notparticularly hard you donrsquot have time to muck around and if things do go horriblywrong it may not be possible to recover Hence preparation is the key have everythingready to go and at hand before you start I actually did a dry run putting the blank inthe vacuum bag and sucking it down just to check I could actually get the board in thebag and to test the vacuum system at full scale For all these steps I worked alone butI would recommend having a helper
There are several different brands of epoxy available in the shops near me FGIWest System Epiglass For the majority of the project I used FGI brand Howevertowards the end I started having problems with it fully curing especially when mixedwith fillers so I switched to West System which seemed more reliable and is less viscousmaking it easier to wet out the fibre
421 CarbonHDF to bottom
Using the planshape template I cut the HDF for the bottom of the board The HDF foamsheets are 2400 mm long so the bottom comprises 2 pieces of foam (ie a back piece andfront piece) There are no complex curves for the foam to follow and hence this step isstraight forward I scraped a layer of thickened epoxy over the blank to assist in sealingit then began the laminating There are several methods for wetting out the carbon Ichose to place the carbon on the HDF and wet out the side of the carbon that will be indirect contact with the polystyrene core Then I flipped the carbon onto the core andcontinued wetting out the side that will be in direct contact HDF I used 480 ml to wetthe approximately 2 m2 of carbon used here I placed peel ply and breather fabric overthe HDF and then placed it in the vacuum bag bottom down The magnitude of themaximum vacuum used was 60 kPa and this tended to pull the nose rocker up higherthan it should be so to counteract this the board (in the bag) was placed on top of therocker off-cut (rocker bed) and then using straps it is pulled down onto the rocker bedOnce dry the HDF was sanded flush to the rail Figure 49 shows the HDF laminatedto the bottom of the board
28
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
Figure 49 After laminating on the 5 mm HDF to the bottom Actually this photo wastaken after laminating the deck so carbon strands can be seen wrapping around therail
422 CarbonHDF to deck
Originally the plan was to laminate the deck and rail HDF in one go I used 5 mmon the deck and 3 mm on the rails The deck piece is cut 40 mm narrower than theplanshape then strips of 3 mm are used for the rails This means there are lots of piecesof HDF to align and while cutting the pieces of HDF it became apparent that it wouldbe very difficult to do the deck and rail in one go So instead the deck piece is laminatedby itself The carbon was cut to be flush with the bottom of the board so after this stepthe rails already have a layer of carbon figure 410 Therefore when laminating on therails I used a lighter weight fibre glass Under vacuum the release film tended to tuckunder the edge of the HDF slightly so once cured I had to trim a couple of mmrsquos off theedge of the HDF
423 Fitting the fittings
Not strictly a laminating step but this is where it occurs in the sequence The centre-board box and fin box are through deck fittings so slots are cut through the board Itwas hard to bring myself to cutting a 1 m long slot for the centre-board box so soonafter laminating it seems such a drastic step figure 411 A channel for the mast trackwas routered as were the cavities for the footstraps and vent plug Thickened epoxyis used to glue in these fittings Note there are different types of micro-spheres usedto thicken epoxy some suited for gluing (strongerhard to sand) and some suited tofairing (lighter and easier to sand) I used pieces of 3 mm thick HDF foam to fill voidsand reduce the amount of epoxy filler required I also glued a stainless steel nut intothe deck to use as an air vent
29
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
Figure 410 After laminating the 5 mm HDF to the deck
Figure 411 No magic trick the saw really does go through the board
30
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
Figure 412 All the pieces of HDF cut and ready to be vacuum bagged onto the rail
Figure 413 All HDF foam on fittings in gaps filled and sanded ready for outer lami-nation
424 HDF to rails
This was actually a very time consuming step Three millimetre thick HDF was usedon the rails Since the rail is curved in both directions many small pieces of foam mustbe cut Particularly near the tightly curved contours at the nose and tail Figure 412shows all the pieces cut and ready to be vacuum bagged onto the rail To glue themon I used 130 gmminus2 fibreglass Lots of masking tape was required to keep them allpositioned before the vacuum was applied Rather than being too ambitious I did onerail at a time as I was a little concerned about keeping it all aligned Once the epoxyhas set any small gaps at the joins are filled and then sanded and faired in to the deckpiece Figure 413 shows the board ready for the outer laminations
425 Outer lamination
The outer lamination is a single layer of 200 gmminus2 carbon except over the fittings wherean extra layer is used The size of these reinforcement patches is given in figure 414The hull is laminated first I allowed about 25 mm to wrap around the rail Howeverbecause of the width of the carbon roll the widest point of the board did not have anyfibre wrapping around the edge I found I needed 780 ml of resin for the 243 m2 ofcarbon which represents a fibre to resin ratio of approximately 40 60 The laminationwas held under vacuum for 12 hours Note before laminating the hull I used a routerto rebate the centre board box to provide space for the gaskets to be glued on laterfigure 413
The deck is slightly more difficult since you must make sure the carbon follows thecurve of the rails with out puckering The larger surface also means around 1 litre of
31
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
Total area of patches = 117 m2
1600times 300 mm
Hull
2300times 300 mm
Deck
weight = 0585 kg
A = 048 m2
A = 069 m2
Figure 414 Size of reinforcement patches
Figure 415 Outer layer of carbon is on
resin is required Working solo I only just go it all wetted out and bagged before theresin gelled (the temperature was 30 oC) I mixed the resin in two 500 ml batches onlymixing the second batch when it was required
43 Finishing
431 Filler coat
I used West System - microlight filler (407) mixed with epoxy to peanut butter consistency(similar colour to peanut butter as well) A very thin layer was then scrapped onto thecarbon-fibre The amount of resin used for the hull was 90 g and for the deck 120 g
432 Gaskets
Before painting I fitted the centre board gaskets Irsquod rebated about 2mm to allow forthe gaskets I used sailcloth folded in half and glued with epoxy glue The thicknessof the gasket is well less than the 2mm so I faired it in slightly to the hull with strips offiller
32
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
Figure 416 After a scraping of filler was applied to the deck
433 Painting
The painting layup was
1 Epoxy primer (3 coats)
2 Two pack polyurethane undercoat (2 coats)
3 Two pack polyurethane overcoat (3 coats)
All the painting was done with a roller and a brushThe filler is effective in filling the residual weave pattern For filling finer imper-
fections I then applied an epoxy primer A primer coat highlights small imperfectionsso I applied filler to these The quality of the original shaping and laminating becomesapparent after a coat of paint is applied There where some small bumps and lumpson the deck and I could pick the join in the two main pieces of HDF which showed asa slight valley These imperfections are small and I decided to live with them I thinkat this stage filling and re-sanding would consume a great deal of time for incrementalgains I decided to accept the imperfections of my shaping and laminating and moveon
After priming I hand sanded with 240 grit sandpaper Then two coats of undercoatfollowed by sanding all over with 400 grit sandpaper Finally three coats of topcoatwith a light sand (400 grit) in between each Note deck grip was also applied seebelow
By the way I used International Paints they provide excellent info an painting us-ing 2 pack polyurethane including a cdrom with movies demonstrating the surfacepreparation and painting techniques really useful
434 Deck grip
I taped a perimeter defining the edge of the deck grip Using the same topcoat paint Imixed in grip particles and applied one coat I mixed in way more grip particles thanrecommend on the tin my past experience is polyurethane is inherently slippery andI wanted to make sure there was sufficient grip The final coat (no particles) was thenapplied over the deck grip coat to prevent the particles being abraded off
33
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
Figure 417 After painting with epoxy primer
Figure 418 Deck grip was mixed into the paint and one coat applied I find mixing itin gives a more even distribution than sprinkling on wet paint
34
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Chapter 5The finished product
The weight of the bare board without footstraps fin or centreboard is 147 kg So this is400 g above my design target This makes sense since I tended to use more resin thanthe 40 60 fibre to resin ratio which is really the minimum resin require to wet out thefibre The weight of the footstraps is 850 g
35
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
36
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
37
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
38
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
51 Photos from Inverloch 25042010
Here are some photos taken at Inverloch Victoria in about 15 knots of wind and usingan 85 m2 sail
39
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
40
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
41
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
42
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
De
sign
an
dc
on
struc
tion
ofa
win
dsurfe
rlon
gb
oa
rd
43
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Appendix ATooling
A1 Compressor
Probably the cheapest way to generate a vacuum is to use an old fridge compressorUsing the suction side of the compressor a vacuum of around 80 of an atmosphere ispossible I bought a 2nd hand one from a whitegoods recycler Irsquove since picked up onefrom the hard rubbish collection Be extremely careful with wiring and ensure no livewires or live connectors are exposed if in doubt place the whole thing in an insulatedbox Figure A1 shows two old fridge compressors one of which is connected to apressure sensor and relay switch
A2 Vacuum controller
You need some way to control the pressure in the vacuum bag Just running the com-pressor continually will create too strong a vacuum which is likely to crush the coreThe pressure in the vacuum system can be visually monitored with a gauge I used athe vacuum gauge from a car tuning kit figures A2 Details of a circuit to accuratelymonitor and switch the compressor on and off according the vacuum level are givenbelow
To control the pressure in the vacuum bag I purchased a differential pressure trans-ducer ($35) I built a circuit that amplifies the (small) output voltage difference fromthe transducer and compares it to the required switch onoff voltages and then setsthe output high (5V) to switch the relay on or low (0V) to switch off figure A6 Basi-cally the circuit should switch off the relay when the vacuum is high and the amplifiedvoltage is 5 volts (rough figure from memory) We want it to stay off and give the com-pressor a rest so the circuit is designed to switch back on at 45V level thatrsquos the theoryanyway However I couldnrsquot get the switch off voltage to be lower than the switch onvoltage (hysteresis effect) For some compressors this does not matter as they will notswitch back on immediately after they switch off they have some circuit which createsa delay before switching back on However other compressors will toggle on-off-on-off if the controlling circuit does not have a hysteresis effect In the end I used an oldcomputer which had analog-digital and digital-analog channels This way I bypassedthe comparator (compare stage) of the circuit and fed the analog out signal of the circuit
44
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
Figure A1 Fridge compressors the one on the left is connected to a pressure sensorand relay switch
Figure A2 Pressure vacuum gauge used for tuning a car engine The gauge reading isindicating 80 kPa below atmosphere atmosphere pressure being around 100 kPa
to the PC A program then samples this voltage and sends an output voltage back tothe external trigger (eg 5V to switch the relay on)
Figure A3 shows the system is use Note I have two compressors running one isquite powerful (must be out of a big fridge) the other one is out of a bar fridge and canjust hold the vacuum (at about 30 kPa) against leaks The reason for two is redundancyin case one fails at a critical moment
Note reading analog voltage signals into a PC requires rather expensive hardwarereading a voltage using a sound card may be possible Sending trigger signals out isno drama as this can be done via the parallel port If you have no easy cheap way tosample a pressure sensor then an alternative is to forget about the pressure sensor andjust switch the compressor on and off at programmed times via the parallel port Thesignal from the parallel port is used to send the onoff relay signal to the compres-sorrsquos relay switch Determining the on-time off-time (duty cycle) for a given baggingoperation would require some trial and error Once the bag is sealed you would runthe compressor until the desired vacuum is achieved then turn the compressor off andtime how long it takes for the vacuum to drop back to the desired ldquoswitch-back-onrdquolevel then turn the compressor on and time how long it takes to pull the vacuum back
45
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
Figure A3 Vacuum system in action In this photo Irsquom bagging on the rail pieces
down This establishes the duty cycle and these numbers are then fed to the PC to au-tomate the process Obviously this method relies on the leakage rate remaining stableduring bagging
A3 Hotwire cutter
To find information on hotwire cutters search Radio Controlled aircraft forums Thehotwire cutter is rather simple just a bow that allows you to tension a wire of requiredlength Figure A4 show the 3 different length bows I used the larger 2 are made from6 mm plywood the small one is a hand jigsaw (make sure the frame is insulated fromthe wire) The wire will extend on heating and for the large bows you need to be ableto retention I used eye-bolts to do this
The wire I used had a resistance of asymp 10 Ωm It seemed around 2 Amps must bepassed through the wire to generate the required cutting temperature (below red-hot)So for a hotwire of 1 m a 24 V power supply rated to a minimum of 24 A is necessary(asymp 60 Watts) However it is useful to be able to control the voltage particularly if youwant to use smaller length hotwires
A4 Hotwire voltage control
The circuit I used to control the voltage is called a ldquochopper circuitrdquo and is generallyused to control DC motors The circuit takes the 24 V supply as an input and outputsa square wave from 0rarr 24 V The ratio of off time (0 V) to on time (24 V) is determinedby an adjustable resistor (potentiometer) You could probably find a circuit design onthe internet I purchased a kit for around $30 which saves a lot of effort and they areeasy to assemble Note $30 is just for the controller you still need a DC power supplyI bought a 24 V one rated to 60 W
46
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
Figure A4 Hotwire bows of lengths 800 mm 400 mm and 150 mm
Figure A5 Variable power supply for hotwire cutter
47
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Design and construction of a windsurfer longboard
minus
+
minus+
+minus
+
minus+minus
Com
pres
sor
BC54
6R
elay
Exte
rnal
trig
ger
220K
LM31
1
2K 2K20
K2K
5V
Vs=
9V
V 2
minusV 1
Not
eV 1
gtV 2
and
V 1asymp
Vs
2
R
R
RR
R
Trig
ger
Com
pare
Am
plif
ySw
itch
Sum
Inve
rt
V 1
Pres
sure
sens
oran
dsw
itch
circ
uit
ieS
ubtr
acti
on
10K
Ana
log
out
Pres
sure
sens
or23
5583
5
K(V
1minus
V 2)
minus(minus
V 1+
V 2)
12V
LM32
4LM
324
Figu
reA
6M
yat
tem
ptat
aci
rcui
tto
cont
rolt
heco
mpr
esso
rno
tper
fect
48
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
bull User Manual West System Cat No 002950
bull need to add some more refs here
49
Board design
Maximum dimensions
Rocker profile
Deck centre-line profile
Vee concaves tail kick
Planshape
Deck cross section and rails
Data files
Design weight
Material costs
Time required to build
Centreboard
Design of centreboard
Aerofoil section
Planshape
Construction of centreboard
Centreboard Box
Mast track fin-box and footstrap plugs
Mast track
Finbox and Footstrap plugs
Board Construction
Shaping
Templates
Core
Rocker and deck
Vee
Planshape
Rails
Laminating
CarbonHDF to bottom
CarbonHDF to deck
Fitting the fittings
HDF to rails
Outer lamination
Finishing
Filler coat
Gaskets
Painting
Deck grip
The finished product
Photos from Inverloch 25042010
Tooling
Compressor
Vacuum controller
Hotwire cutter
Hotwire voltage control
References and links
Appendix BReferences and links
bull Building a composite windsurfer wwwecboardscouk
bull Building Custom Sailboards and Surfboards Sail amp Surf Tech Guide-4-698 SP Sys-tems Composite engineering Systems (the only brief reference to building a race-board that Irsquove found)
bull How to Build Your First Surfboard by Stephen Pirsch wwwsurferstevecom
bull Swaylocks forum wwwswaylockscom
bull Vacuum Bagging Techniques West System Cat No 002150
