Hagedoorn - Inventing the Hapa

Geophysical Prospecting, 2001, 49, 735±745

J.H. Hagedoorn ± inventing the Hapa: A review of a geophysicist's

òther' work and how it inspired others

Theodor Schmidt*TO Engineering, OrtbuÈhl 44, 3612 Steffisburg, Switzerland

Received July 2001, revision accepted July 2001

A B S T R A C T

This paper describes J.G. Hagedoorn's work on ùltimate sailing' ± the combination

of a manned kite and a water kite called a Hapa, constituting a minimal sailing

system ± and the way others have taken up his challenge to sail while suspended from

a kite. Hagedoorn's goal has not been entirely achieved, but `near' and partial

solutions have been reached. Kite-Hapa-sailing continues to pose a `Holy Grail' type

challenge to many kite-sailors.

I N T R O D U C T I O N : E A R LY H A PA S

Besides his professional geophysical work, Hagedoorn had

another scientific interest, which he pursued as an amateur.

It is a field so exceptional that he was able not only to

invent it and give it a name, but also to inspire dozens of

enthusiasts and become known to thousands of people

outside geophysics, and that with only two publications!

The title of his 40-page principal monograph, Ultimate

Sailing (Hagedoorn 1971), describes the subject. Hagedoorn

managed to reduce the concept of the sailing boat, which

usually consists of a hull, a keel or centreboard, a mast and a

sail, to a simpler system consisting of a kite in the air, a line

and a kind of water-kite for which he coined the name `Hapa'

(HAgedoorn-PAravane), liking its vaguely Polynesian sound.

The components of Hagedoorn's concept were already

known. Kites have been used to propel boats for many years,

beginning perhaps with the above-mentioned Polynesians and

later the great thinker Benjamin Franklin, then in earnest by

the Englishman George Pocock (1827/1851), who mainly

undertook long journeys in southern England by means of his

kite-powered carriage and who described man-lifting kites

for nautical use. More recently kites have been used by

members of the Amateur Yacht Research Society (AYRS) with

whom Hagedoorn corresponded. His Hapa or water-kite is

also not entirely original, similar devices having been used for

mine-sweeping, fishing and oceanographic work. Many

synonyms are in use, such as paravane and `chien-de-mer'

(sea dog). As early as 1845, a Dr Collodon operated a model

kite-Hapa on Lake Geneva (see Fig. 1). Burgess (1939/1995)

suggested sailing buoyant airships with paravanes. O.W.

Neumark flew buoyant kites from motorboats, but lacked

any sort of Hapa (Morwood 1961).

Hagedoorn was the first to suggest coupling such a device

to a manned kite, instantly forming a minimal sailing system,

but still a proper one capable of travelling upwind. Air-

inflated kites known as parafoils had just been invented and

were used by parachutists to glide through the air a distance

several times greater than the altitude from which they

jumped. Hagedoorn's concept was to equip such aviators

with his Hapas, which they could fling into the water while

still flying and, with sufficient wind, immediately begin to

sail in this new mode, becoming àquaviators' capable of

unlimited travel without even getting wet, as long as the wind

lasted. The Hapa was thus not to be merely a sailing novelty

or thought experiment, but a device for rescue and possible

military use.

In the early 1970s, Professor Jerzy Wolfe and his students

at the Polish Aerodynamics Institute in Warsaw built and flew

a `paravane hang glider', apparently with many crashes, but I

do not know whether there was any connection between

Wolfe and Hagedoorn (Bradfield 1979).

q 2001 European Association of Geoscientists & Engineers 735

*E-mail: [email protected]

After having established the theoretical feasibility of the

Hapa, Hagedoorn undertook to make a scale prototype

himself. The first Hapa was a beautiful piece of work but it

simply did not work. The second model was disc-shaped to

avoid directional instability. With this prototype, drag tests

were carried out in a local canal (see Fig. 2). Hagedoorn

drove his car along the canal and the line was held by one of

his sons. At low speeds, the system was stable. Thanks to a

forward mounting, the Hapa was more or less at right angles

to the direction of propagation. At higher speeds, however,

the kite started to oscillate and the Hapa jumped out of the

water. An improvement was achieved by allowing the disc to

rotate freely, without creating a torque. The other end of the

system consisted of a parafoil. Hagedoorn went to the US for

its purchase, but it came without any instructions. A crash

landing on the heath caused him to perform his duties as

professor with a neck-band for several weeks. Another series

of tests was conducted, in which one of his sons was equipped

with a parafoil and pulled in the air behind a motorboat.

This once resulted in a spectacular splash from about 30 m

height ± but at least it was better to land in the water than

on dry land. The Hagedoorns faced the same problems as

the very first designers/flyers of aeroplanes. Not only had

they to build a plane, but they also had to learn to fly it. The

idea of launching the Hapa when the flyer is pulled up behind

a boat, thus achieving forward movement, was alas not

achieved as the instability problems persisted. A recent

picture of the last and best-performing prototype is shown

in Fig. 3.

Realizing that further progress and development could be

made only with more human resources, Hagedoorn put pen

to paper and produced the manuscript Ultimate Sailing in

1971. In the years thereafter Hagedoorn tried to arouse

interest amongst professional maritime journals and institu-

tions, without success. He then turned to Scientific American,

which published a synopsis of his manuscript in 1975.

Belatedly, in 1994, the full manuscript was published by the

Amateur Yacht Research Society.

This paper gives more details of the development of the

Hapa and describes some of the ways it has been

implemented and put to use.

D E V E L O P M E N T A N D I M P R O V E M E N T O F

T H E H A PA

Hagedoorn developed his idea of the sailing Hapa by first

examining a type of sailing craft known as the Pacific, or

flying, proa. This is a slim Micronesian outrigger craft which

is normally stabilized by the crew balancing the forces of the

wind by climbing on the outrigger `flying' just above or on

the water-surface. Members of the AYRS, notably Edmond

Bruce (Bruce and Morss 1965/1970/1976), realized that a

single hydrofoil attached to the outrigger could perfectly

balance all sailing forces ± in steady-state conditions.

Figure 1 Collodon's self-steering kite-Hapa,

1845.

736 Th. Schmidt

q 2001 European Association of Geoscientists & Engineers, Geophysical Prospecting, 49, 735±745

However, the sea is not `steady-state' and the craft remains a

highly capsizable object. Hagedoorn suggested using a curved

foil as shown in Fig. 4, but quickly went on to suggest that by

separating the structure of the sail and the hydrofoil, all

forces could pass through a single line, provided the hydrofoil

could be induced to keep its required attitude and angle by

itself, following the water-surface faithfully on its leash. He

was especially worried about the Hapa's pitch angle, i.e. its

rotation around the axis of the connecting line, and thus

suggested not only using a perfectly circular meniscus-shaped

hydrofoil, but also attaching this through a ball-bearing, so

that no pitching moment whatsoever could arise from the

foil. A float is still needed in order to ensure the proper depth

of the foil just below the surface, and a fin on the float is

required so that it will track in the proper direction. Figure 5

shows Hagedoorn's drawing of his Hapa and the way it might

be used to stabilize a sailing dinghy.

Hagedoorn's next step was to free the boat's working parts

± the airfoil (sail) and the hydrofoil (Hapa) ± completely, by

replacing the sail with a kite, doing away with the hull and

mast entirely and suspending the pilot from the kite. Figure 6

shows the final concept developed in Ultimate Sailing.

Hagedoorn provided a detailed theoretical basis and con-

jectured various ways in which the system might actually be

used in practice. Then, with the publication of the article in

Scientific American (Hagedoorn 1975), more people took up

the challenge.

I read this article while a student and immediately built a

Hapa to Hagedoorn's specification. I spent many hours

experimenting with it in the strong current of the Rhine at

Basel, trying to improve its efficiency, expressed by the angle

between its line and the normal to the direction of travel or

flow (the drag angle). For an ìdeal' Hapa, this would be 08. A

circular foil is intrinsically inferior in this respect to more

slender, higher aspect ratio foils. Therefore I made wing- and

hoop-shaped Hapas and experimented with a depth sensor

designed to keep them just below the surface at all times. The

problem with these more efficient Hapas was that they would

suddenly become unstable if pulled too hard or fast, either

diving to the bottom or jumping in the air. Still, they worked

and achieved drag angles as low as 188. I attached kites to

these Hapas and sailed them across ponds, achieving

Hagedoorn's goal in a very small (unmanned) way. After

finishing my degree in physical oceanography in Wales, I

would have liked to develop kite-Hapas as autonomous

sailing oceanographic instruments, but was unable to get very

far with this. I had been corresponding sporadically with

Hagedoorn, but letters always took many months and, most

Figure 2 Hagedoorn's second Hapa in action in the Oegstgeester Kanaal, about 1972 (provided by the Hagedoorn family).

Inventing the Hapa 737


unfortunately, everyone in the AYRS believed a rumour that

he had died ± many years before his actual death ± so it is

possible that he never knew about the very slowly ripening

fruits of his work in this field.

In 1980 I went to a symposium on wind propulsion of

commercial ships, where I met kite manufacturer Keith

Stewart, who immediately offered me a job ± designing

Hapas! Stewart was in contact with AYRS member Didier

Costes from Paris, who had built some very efficient Hapas

indeed (drag angle of about 108), wanting to use these to

stabilize and speed up his highly experimental triscaph

Exoplan. Costes' Hapas, like Hagedoorn's original, had to

be manually flipped in order to change direction, and since

Stewart was interested in selling autonomous sailing devices,

I was installed in Dorset designing remote-controlled Hapas!

Both these and the kites were radio controlled. This was not

required for steering, as the kite-Hapa combination is

automatically self-steering, but rather for changing the

course: all points of sailing up to `fine reach' (slightly

upwind) were available. Downwind was achieved by setting

the kite and the Hapa on opposite tacks. Figures 7 and 8

show some of these devices in use (Schmidt 1984, 1985/1995,

1991).

The usual type of Hapa-symmetry did not allow a kite-

Hapa to tack: unlike a sailing boat there was too little inertia

to carry it through the eye of the wind. I therefore went back

to the proa-type symmetry and constructed a bi-directional

Hapa which simply changed direction by shifting the point of

line attachment ± also by remote control ± and which also

had a `pure drag mode' for drifting slowly downwind with

the wing stalled. Successful as these experiments were, the

devices were too small to support a pilot; the most that could

be carried aloft was a camera.

Quite independently, William Roeseler (Roeseler and

Funston 1979) suggested sailing sailplanes on the sea using

Hapas, which he called `fish'. He later tried this in practice

and was able to fly devices from motorboats, but not actually

sail them.

F U RT H E R H A PA E X P E R I M E N T S

A keen follower of the Hapa concept was Roger Glencross, a

London accountant who wanted to achieve Hagedoorn's aim

in practice: that of sailing a manned kite-Hapa, with the pilot

supported in the air. In Ultimate Sailing, Hagedoorn had

shown this to be theoretically feasible, but much work

remained to make it work in practice, the major hindrance

being the issue of safety. The combination of heights, strong

forces, unstable components, tangled lines and water is a

formidable opponent. Glencross started building Hapas of all

shapes and sizes, testing them on a pond. Besides this, he

purchased a hang-glider and later several paragliding

canopies, now much more advanced and cheaper than the

first Jalbert parafoil that Hagedoorn used. I helped him fly

them in the wind in Portland Harbour, always only a short

distance above the ground, but enough to prove that with a

Figure 3 Hagedoorn's last Hapa working prototype (provided by the Hagedoorn family).

738 Th. Schmidt


steady wind of the right strength and a Hapa of the right

dimensions, it would be quite possible to sail airborne at

roughly right angles to the wind. One day we were nearly

successful: we had tried out one of Glencross's Hapas from a

motorboat and measured its forces and angles. The same day

we produced the same forces and angles suspended from the

paraglider in the wind. However, we never got the two

devices together under the required conditions. Every year

Glencross gets a little closer, but the combination of

conditions needed continues to elude him: a suitable wind

window (not too much and not too little), the right state of

the tide, a safety boat in readiness, the equipment in good

condition and enough competent helpers (Glencross 1993,

1996; Kitson 1994; Schmidt 1994/1996).

The main problem is getting started. I do not think

anybody has yet seriously contemplated Hagedoorn's ulti-

mate concept of launching the Hapa while free-flying in the

air, but even simpler methods, like starting from a motorboat,

require considerable resources and experience. The only

method useful in practice would be for the pilot to start

unaided in the water or at least from shore. This would

require entering the water with the Hapa ready to be released

from a backpack or some similar arrangement. This is not

very complicated, but nobody seems yet to have tried it. What

has been achieved is to travel sitting on a commercial

hydrofoil called an àir chair' while being propelled by a kite

instead of the usual ski-boat. Cory Roeseler (1997), the son of

W. Roeseler and the first expert kite water-skier, described

this in detail. In contrast to Hagedoorn's scheme, the

hydrofoil does not pull, but rather supports the pilot, but

Roeseler described brief uncontrolled excursions in `Hage-

doorn-mode', resulting in some back injuries, and has

understandably been reluctant to continue this line of

experimentation.

Great progress has also been made by kite-surfers who rush

around at great speeds in perfect control, sometimes also

leaping high into the air, momentarily becoming air-

supported. This has also been achieved on snow by Dieter

Strasilla, Andrea Kuhn and Wolf Beringer, who also

experimented with sailing airborne, with and without

`snow-Hapas' in the form of a second skier (Hanschke

1976; Beringer 1996). So, gradually, Hagedoorn's still elusive

goal is approached from all sides, and all that is really

required to achieve it is for somebody to combine a kite-

surfer's skills and boldness, the knowledge accumulated by

Hagedoorn and others, and Glencrossian perseverance.

H A PA S F O R S A I L I N G

With ùltimate sailing' in mind, Hagedoorn dwelt only briefly

Figure 4 The flying proa stabilized by a

curved hydrofoil (from Ultimate Sailing).



on using Hapas for stabilizing actual sailing craft. Others

have investigated this use, in order to carry more sail and

achieve higher speeds without acrobatics or large outrigger

structures. In Fig. 9, I am shown in a folding canoe using

a Costes Hapa. Many years later, Robert Biegler (2001)

Hapa-sailed the same canoe extensively and methodically.

The main experimenter in Hapa stabilization is Paul Ashford

(1990, 1994), whose article `Seadogs for monohulls' is

published with Hagedoorn's reprint of Ultimate Sailing in

AYRS Publication No. 114 (1994). Ashford compared Hapas

(which he calls `doggers') with fixed hydrofoils and ballast.

He tested and measured numerous models, which achieved

drag angles as low as 108, and also full-sized Hapas intended

for his 7 m yacht. His work continues.

Costes (1994/1996, 1995) also continued to improve and

patent his `chiens-de-mer', intending to use them for sailing

with blimps or Zeppelins, as shown in Fig. 10. Some full-

scale work with the airship `Zeppy-2' actually commenced

(apparently at the cost of a broken leg), but this was too

rounded and had too little wing surface to sail upwind. A

design intended to correct this, his `planostat', was never

built.

Hapa design continues to fascinate, and one of the latest

models by John Perry is pictured in a paper by Quinton

(2001).

C O N C L U S I O N S A N D O U T L O O K

When I first read Ultimate Sailing 25 years ago, I was

convinced that I would be able to build and àquaviate' with a

personal Hagedoornian kite-Hapa within a short time.

However, this has not been the case because sound engineer-

ing and physics, dedication and perseverance, encouragement

and money, skill and daring are all required, and so far all

experimenters have been lacking in at least one of these items.

What is the present state of the art and what is needed finally

to achieve Hagedoorn's goal or even more?

Figure 5 A sailing boat stabilized by a Hapa

(from Ultimate Sailing).

740 Th. Schmidt


The system

Hagedoorn's classic system uses a kite attached to the pilot by

short lines and a Hapa on a longer line. One of the main

reasons that this has not yet been implemented is the safety

concern: a high perceived risk for a moderate perceived gain.

Also, the system will not work in light winds and requires

considerable logistics at least to begin with. The extended

system I would like to see would allow the pilot to be

attached anywhere on the line between kite and Hapa and

would include a boat-like nacelle for winds when not

enough force is available to lift the pilot's weight. Long

lines allow the kite to be used at an elevated altitude with

more wind. Remote-controlled systems have already been

implemented; the extended system would mainly involve

scaling these up sufficiently to carry a person and equipment.

Adding propellers and electrical power systems to the

Hapa and perhaps also to the kite would facilitate launchings

and extend the possible range of operation. All this is

possible today since the components exist, but it requires

somebody to build them large enough and to put them

together.

The kite

Parafoils as used by Hagedoorn and Glencross have come a

long way. They can now be launched in very little wind and

are very efficient (high lift-to-drag ratio). However, once in

the water they cannot easily be launched again. Kite-surfers

have now developed waterproof and water-launchable kites,

but they use up to four lines and little attention has been

given to launching systems. Inflated and also buoyant kites

have proved excellent in moderate winds but difficult to

handle in strong winds. What is needed is the combination of

the best of the above systems. The ideal sports-kite must be

water-launchable, yet it must have a mechanism to reduce its

pull for handling and emergencies. The best kite for an

extended system would be shaped like an inflated wing with

electrical yaw and pitch control, and would thus take up any

Figure 6 Ultimate sailing: the aquaviator

sailing by parafoil and Hapa (from Ultimate

Sailing).



desired line tension and angle possible within the wind

window available, and this would be on a single line. A

control system would maintain the desired settings auto-

matically. Solar cells would power the system, perhaps also

with enough power left over for propulsion in light winds.

For this, the kite might be equipped with propellers or be

rotary in nature, allowing either high forces in àutogyro' or

electrically powered modes, or the harvesting of excess

energy in stronger winds (i.e. an airborne wind turbine).

For long trips, the kite would be buoyant and have an

integrated small solar-powered electrolyser for replenishing

hydrogen.

The Hapa

Present Hapas are either too small for starting the system or

too large for travelling quickly. What is needed is a multiple-

wing geometry or indeed several Hapas of different sizes

Figure 7 A Costes Hapa and Stewkie inflated kite on a fine reach (T. Schmidt).

742 Th. Schmidt


behind each other. A Hapa for the extended system would

have an electronic controller communicating with the kite in

order to maintain the desired line tension, direction and

course. It would be able to stay on the surface or operate at a

set depth. A control system would ensure that the Hapa does

not jump out of the water when pulled hard, as is sometimes

the case with present designs. This technology already exists

for hydrofoil boats. A certain amount of electrochemical

energy storage would allow operation in periods of adverse

conditions and facilitate launching procedures, for example

using additional propellers.

The line

This should be streamlined at least near the Hapa. For the

extended system it should be able to transmit electrical power

between the Hapa and the kite. A variation would be a

looped endless line or a torque-resistant component able to

transmit mechanical power.

The nacelle

This would be the pilot's crow's nest, suspended from the line

and able to move up and down along it. In low winds, the

nacelle would float and act as a boat. It would also have its

own adjustable hydrofoil for launching and low-speed

operation.

Future uses

Our third millennium aquaviator might not be Hagedoorn's

suggested military pilot but an oceanographic researcher. A

typical trip might go like this:

You cycle to the hangar where a number of kite-Hapas are

stored, pick the one with a nacelle for overnight trips and

manoeuvre the contraption to the dock on its dedicated

trolley, the kite being completely feathered for this operation.

The wind is onshore, so the Hapa must first pull kite and

nacelle outside ± using stored electrical energy ± like a

Figure 8 A radio-controlled Stewart/Schmidt hoop Hapa.



veritable sea horse. You remain on the water-surface until you

have cleared the harbour. Freeing off a bit, the Hapa's main

foil begins to work and, speeding up, the line tension

increases sufficiently so that a touch of the joystick pulls

the nacelle free from the waves. Now the speed increases even

more, and rapid progress is made to deep water. You now

advance the nacelle towards the kite and make the Hapa dive,

collecting data and water samples. With the computer doing

all the work, you have time to take aerial videos of the

inquisitive dolphins nearby. As the light begins to fade, you

reduce the speed for safety and the Hapa is power-parked

with sufficient force to keep the nacelle suspended, so that

you may enjoy a restful night, gently swaying in the arms of

an airborne Morpheus.

A C K N O W L E D G E M E N T S

Hagedoorn's eldest son, A. Hagedoorn, was extremely

helpful in obtaining some of the material presented and in

checking parts of the Introduction. Gerhard Diephuis

provided much of the biographical information, procured

the pictures of Hagedoorn's Hapas, and was very helpful with

suggestions and corrections. Roger Glencross was instru-

mental in getting this paper written and was the driving force

in keeping Hagedoorn's goal of ùltimate sailing' in our

minds. Apart from those mentioned in the text and

references, many others have also helped with ùltimate

sailing' experiments ± to them also my thanks. Last but also

foremost, my thanks go to Professor J.G. Hagedoorn himself,

for sharing his ideas with us.

Figure 9 A Hapa-stabilized folding canoe (C. Finlayson).

Figure 10 An airship sailing with Hapa (from D. Costes' French

patent no. 443 378).

744 Th. Schmidt


R E F E R E N C E S

Ashford P. 1990. Stabilising paravane experiments. Low Drag Craft.

AYRS Publication No. 107.

Ashford P. 1994. Seadogs for monohulls. Ultimate Sailing: The Hapa

Revisited. AYRS Publication No. 114.

Beringer W. 1996. Parawings. Verlag fuÈ r Technik und Handwerk.

Biegler R. 2001. Taking a `seadog' for a walk. AYRS Catalyst 1, 24±

25.

Bradfield W.S. 1979. High speed sailing vehicles. Speed Sailing. AYRS

Publication No. 93.

Bruce E. and Morss H. 1965/1970/1976. Opinions about Hydrofoils.

AYRS Publications Nos 51, 74 and 82.

Burgess C.P. 1939/1995. Sailing airships at sea. Reprinted in Ultimate

Sailing III. AYRS Publication No. 118.

Costes D. 1994/1996. Windsailing for airships and gliders: using the

`Seadog'. Ultimate Sailing IV. AYRS Publication No. 122.

Costes D. 1995. A description of some seadog inventions. Ultimate

Sailing III. AYRS Publication No. 118.

Glencross R. 1993. Sailing craft Hagedoorn. AYRS Projects. AYRS

Publication No. 112.

Glencross R. 1996. Kites and Hapas at Speedweek 1996. Ultimate

Sailing IV. AYRS Publication No. 112.

Hagedoorn J.G. 1971/1994. Ultimate Sailing: Introducing the

Hapa/Ultimate Sailing: The Hapa Revisited. AYRS Publication

No. 114.

Hagedoorn J.G. 1975. Ultimate sailing. Scientific American, March

(page numbers unavailable).

Hanschke T. 1976. Segeln auf Gletschern. Alpinismus 12.

Kitson T. 1994. The experimental craft at Weymouth 1992±4. Speed

Sailing and Speed Weeks 1992±4. AYRS Publication No. 115.

Morwood J. 1961. An inflatable kite. Aerodynamics I. AYRS

Publication No. 37.

Pocock G. 1827/1851. The Aeropleustic Art. Facsimile reprint, 1 Jan

1969, by Edward L. Stearn, San Francisco, CA.

Quinton B. 2001. Winds of change: a rally for innovative watercraft.

AYRS Catalyst 1, 5.

Roeseler C. 1997. A field study of kite-powered hydrofoil theory.

Transport Sailcraft. AYRS Publication No. 124.

Roeseler W. and Funston N. 1979. The Sea Nymph and the

ancient Egyptian Yacht. The Ancient Interface Sailing Symposium

1979, Pamona, CA. AIAA.

Schmidt T. 1984. Unusual sailing systems for kites. The Naval

Architect E, 75±76.

Schmidt T. 1985/1995. Hapa development 1980±1985. Reprinted in

Ultimate Sailing III. AYRS Publication No. 118.

Schmidt T. 1991. A short history of Hapas. Foils and Hapas. AYRS

Publication No. 108.

Schmidt T. 1994/1996. Hagedoorn, Glencross and the Hapa.

Ultimate Sailing IV. AYRS Publication No. 122.

N O T E

Copies of AYRS publications or photocopies of articles may

be obtained by writing to: Amateur Yacht Research Society,

BCM AYRS, London WC1N 3XX, UK.



Documents

Hagedoorn - Inventing the Hapa