Procedure for Ship Propeller Renewal

8/19/2019 Procedure for Ship Propeller Renewal

1/24

Procedure For Ship Propeller Renewal

Propeller is the most significant machinery system of the ship. No matter what type of propeller it is, ship owners never make compromises on such important equipment as itdirectly affects the efficiency and safety of the vessel. Here we discuss about fixed pitchkeyless propeller renewal.

Why is propeller renewed?

There are various reasons for which a ships propeller could be renewed. !ome of thesignificant reasons are"

#$ %amage to the propeller

&$ %ynamically unbalanced

'$ (enewing the existing propeller with a new propeller that is of better material, larger blade area etc.

)elow we will learn about the procedures involved in renewing a propeller.

)efore decoupling the intermediate shaft and the propeller shaft *tail shaft$, makethorough inspection of the propulsion system. +enerally, the shaft ack up test is donebefore removing the intermediate shaft.

http://www.marineinsight.com/sports-luxury/equipment/propeller-types-of-propellers-and-construction-of-propellers/http://www.marineinsight.com/marine/marine-news/headline/controllable-pitch-propeller-cpp-vs-fixed-pitch-propeller-fpp/http://www.marineinsight.com/marine/marine-news/headline/controllable-pitch-propeller-cpp-vs-fixed-pitch-propeller-fpp/http://www.marineinsight.com/marine/marine-news/headline/controllable-pitch-propeller-cpp-vs-fixed-pitch-propeller-fpp/http://www.marineinsight.com/marine/marine-news/headline/controllable-pitch-propeller-cpp-vs-fixed-pitch-propeller-fpp/http://www.marineinsight.com/sports-luxury/equipment/propeller-types-of-propellers-and-construction-of-propellers/


2/24


3/24

-igure '" 1ntermediate shaft removal

-igure 5" 1ntermediate shaft removal


4/24

4nce the intermediate shaft is removed and secured in a safe location in the ship, checkthe condition of the plumber block bearings. 0ook for any white metal debris or contactmarks.

1mage 6" 1ntermediate shaft bearingThe tail shaft removal is done in the dry dock.

7 -or this, the first step is to cut the rope guard and keep it aside. Propeller cone is to beremoved and then slack the aft stern tube seal *prior to which stern tube oil need to bedrained$.

7 Then propeller nut is removed *make sure reference point is marked on the tail shaft$and the propeller is secured prior to the tail shaft removal.

7 0ifting and shifting arrangements need to be pre8planned.

7 (emove the forward stern tube seal and then pull the tail shaft and shift to the lifting9one: in some cases tail shaft can be removed through the skylight but in most cases it

requires cutting ship side shell for access. Tail shaft is carefully pulled out through thestern tube and removed through the access. 1t is advised to perform N%T on the tail shafttaper area.


5/24

-igure ;" Tail shaft removal


6/24

-igure


7/24

-igure >" Propeller 7tail shaft bedding


8/24

-igure @" Propeller 7tail shaft beddingPropeller Mounting

4n completion and satisfaction of propeller bedding, tail shaft and other accessories thatare removed are installed back. Then the propeller is mounted. This is a significant stageand careful attention is paid during the same. Here we will discuss about the oil inectionmethod for a keyless propeller mounting.

#$ 3lean the propeller boss and the propeller shaft

&$ !lide the propeller to the propeller shaft and align to the match marks. *Prior to thisstep, remember to record the temperature of propeller boss and propeller shaft$

'$ !crew in the Pilgrim Nut


9/24

5$ %ry fit" 2ctuate the high8pressure pump connecting the Pilgrim nut, allow the propeller to slide in to certain distance and set the dial indicator to 9ero. The maker alwaysrecommends initial load

6$Aet fit" Then actuate the high pressure pump connecting the propeller boss expansionoil port and simultaneously actuate the nut pressure pump. (aise the pressure graduallyuntil the predetermined push up length is achieved *determination of push up length is

explained below$

;$ 4nce the required push up length is achieved gradually release the pressure of bossexpansion port and then release the nut pressure

$ (emember to take shaft ack up test post the installation

@$ /erify the coupling alignment using sag and gap method

Propeller mounting arrangement


10/24

-igure #=" Propeller push up arrangement


11/24


12/24

2lternatively, there are graphs provided by manufacturer, which can be used in lieu of theabove8mentioned formulae recommended by the class.

Permissible push up length can be captured for the corresponding temperature.

Conclusion

Propeller renewal is not about removing the existing propeller and ust installing the newone, there are many other significant factors to overcome. -ollowing are important pointsto be taken care of"

#$ +ood interference fit to transmit the torque" %amaging factor here is the varyingtemperature and differential thermal expansion of the propeller hub *bron9e$ andpropeller shaft *steel$.

Thermal expansion coefficient of bron9e is about #= and steel is about < *in #= 8;

inB-ahrenheit$. This will affect the fitting, hence keeping all this in mind required push uplength is calculated such that the sufficient friction is achieved to transmit the torque.


13/24

&$ (educed stress on propeller hub and propeller shaft" /on misses stress should be lessthan =.< times yield stress of propeller material. /on misses criterion is one of the mostcommonly used failure theory.

To assess the von misses stress"

#$ %erive the stress elements

&$ -ind the principal stresses *Cohrs circle$


14/24

'$ -rom the principal stresses von misses stress can be derived *for &d$. 1f it is greater than the yield strength, then the material fails. 1t is ust a simple explanation about vonmisses stress. Taking all these into account, maker represent the minimum push uplength graphically.

Note" The above description of propeller renewal may slightly vary with ships butunderlying concept is similar in all the cases.

4ver to you..

%o you know about more points that can be added for the propeller renewal procedureD

0ets know in the comments below.

EEE

T#"% SFT S'R()*


15/24

+uide ,otes on Tail shaft Sur-ey

./ Propeller Shafts

./. Propeller Shaft Clearances 0 Measurement

Periodical docking surveys and periodical propeller shaft surveys are incomplete without

propeller shaft clearances. These may be determined as bellows"

• Ahen the shaft is removed for survey or maintenance, by calibration of ournalsand bearing bores.

• Ahen bearing is exposed with shaft in place for partial survey or seal

maintenance, by leveler gauges, or soft wood wedge driven between shaft andbearing then measured with calipers.

• Normal running condition, by poker gauge comparing readings with previous

measurements.

•

1n normal running condition, by lifting shaft and measuring the lift by dial gauge*0ess accurate$. 3ase needed to avoid undue force. 2ssessment of poker gaugereadings can only be made if records of the previous readings are available andthe relative shaft clearance is known. Poker gauge readings taken in isolationproduce no reliable value of bearing clearance.

N4TF" Ahen stem tube bearings are renewed or re8metallic, clearances will be back to

original. 4n refit, it is essential that these clearances are recorded and also the

corresponding new poker gauge readings for future comparison.

Aith most modem stem tube seal designs, the poker gauge measures from the seal box

G4% to the seal sleeve G4%. Hence, whenever the seal is fitted with a new sleeve or the

sleeve is machined, the poker gauge readings Gas fitted should be recorded in

conunction with the measured clearance, by feeler gauges, calibration or both, since the

bearing will be accessible during seal overhaul.


16/24

./1 Propeller Shaft Clearances 0 "nitial and Ma2imum #llowed

#.&.# The following clearances are intended for the guidance of !urveyors.

(ecommendations of designers and manufacturers may differ and the !urveyor should

take notice of these in deciding whether departures from the values given here are

ustified.

1n the case of initial clearances drawings should be checked and for special materials

such as GTufnol the manufacturers technical information should be heeded to allow for

expansion of the bearing material on submersion in water.

#.&.& Propeller shafts running in white metal bearings 8 oil lubricated.

http://4.bp.blogspot.com/-YmZkjhVInYY/URoY2WTA0dI/AAAAAAAACes/95AW60bE8_8/s1600/m.JPGhttp://4.bp.blogspot.com/-YmZkjhVInYY/URoY2WTA0dI/AAAAAAAACes/95AW60bE8_8/s1600/m.JPG


17/24

#.&.' Propeller shafts running in lignum8vitae or ITufnolI type lined bearings water lubricated"


18/24

N4TF" The stern gland should be repacked or at least partially repacked at each

periodical bottom survey.

#.&.5 Propeller shafts lubricated by grease.

./3 Crac4 detection of propeller shafts

#.'.# 2rea to be crack detected.


19/24

#.'.& 3rack detection may be by dye penetrant method or magnetic particle method.

Cagnetic particle inspection is preferred because it is more sensitive when properly

carried out.

1n both cases the area to be checked must be thoroughly cleaned. Ahere possible a

qualified technician is preferred working to recogni9ed standards.


20/24

The sensitivity of the magnetic particle inspection is easily checked using a field strength

indicator *burmah castrol strip$.

1f cracks are detected and not easily removed by light polishing it is advisable to check

the crack depth by ultrasonic before proceeding.

#.'.' 1t is allowed to reduce the rule diameter by ' ? *corresponding to a decrease in

torsion strength of #= ?$ by machining or grinding. Therefore if crack depth deeper than#.6 ? or shaft diameter *shaft being rule si9e$ the shaft shall be reected. (epairs of

corroded or cracked shafts within limits given above shall be smoothly ground out to

reduce stress concentrations to a minimum. The hollows should be filled with propriety

metal filler if in way of sealing rings etc.

!light surface defects *corrosion or cracks$ can be machined out provided that rule

diameter is not reduced by more than ' ?.

#.'.5 1n the case of a propeller8shaft in normal steel and the propeller hub in stainlesssteel, the holes of the propeller8flange and the propeller8flange itself have to be carefully

inspected for electric8chemical corrosion.

!eawater has to be avoided and adequate protection is to be foreseen.

./5 Repairs to Propeller shaft cone


21/24

3orrosion on the conical part of the propeller shaft may be repaired by machining the

taper.

This will result in the propeller moving forward which must be contracted by fitting a

spacer between the shaft couplings. The maximum thickness allowed for this spacer is

&6 ? of the intermediate shaft flange thickness. 1t is therefore the intermediate shaft

flange thickness which determines the maximum amount which can be machined off the

cone.

e.g. 1ntermediate shaft coupling flange thickness #== mm, then maximum spacer which

may be employed J &6 mm, if propeller shaft taper J # in #& the radial amount which may

be machined J &6B#&J approx. & mm/

!urface contact of propeller bore to shaft cone should be checked using Prussian blue.

There should be a minimum of


22/24

2rrangements are to be made to allow any air present in these spaces to escape at the

moment of filling. 1t is recommended to test these spaces under a pressure at least equal

to that corresponding to the immersion of the propeller in order to check, after filling, the

tightness obtained.

./7 Propeller shafts with !ron8e liners

#.;.# +eneral

2lways check carefully the inboard part of the shaft where water from the stern gland

may have caused corrosion cracking, characteristic K8shaped fissures particularity on thecoupling -lange filled. This part of the shaft is best protected by a special coating.

)eware also of electro8chemical corrosion in the region of the end of the liner.

The bron9e liners protect those parts of the shaft which would otherwise be in contact

with sea water.

3ontinuous liners 8either in one piece or in several sections cover the shaft from forward

propeller boss to forward part of the stern gland. Parts of liner most liable to wear are

those in way of stern gland packing, or the liner can be eroded by vibration or hammering

of the shaft. !u obected to torque reaction with the shaft: the liner can crack *on its

surface, or in other places$. 3racks may also result from occasional over8heating. !ea

water can seep through the cracks and cause rapid corrosion of the shaft.

4ther types of corrosion are the result of liner assembly. 0iners are generally held to tail

shaft by shrinkage. !hafts are submitted to helical stress and it is unlikely that the same

distortions are equally applied over the whole length of liner.


23/24

!uch fretting is often the cause of corrosion noted under aft extremity of liners where sea

water filters in. Ahat has been said about shaft and liner relative motions is also true for

liner sections connected by *hammered or shrunk$ red copper oints. 3onnections of two

adacent liner sections are submitted to torque reactions and if copper oints no longer

ensure the necessary water tightness" corrosion is then frequent under oints and

adacent area.

#.;.& Chec4ing the fit and condition of liners

The !urveyor shall hammer test the liner and oints between sections 8 bearing in mind

that liners may be chamfered beyond the bearing surfaces and will, therefore, give a

different sound, not to be mistaken with that of a slackening liner.

!lackness is usually noted at extremities of liner. 1t may be caused by heating *of aft

bearing, gland$ or cracks in liner.

The !urveyor shall also examine carefully the surface of the liner for cracks or porosity,and if in doubt, he will carry out a non8destructive check.

2ny cracking or slackening of the liner *especially all, next to propeller$ or loosening of

copper oints will result in corrosion of the shaft.

for such defects, loose copper oints will need to be withdrawn and the liner surface in

way machined off and other corroded areas should also be machined so that the shaft

surface can be inspected.

The !urveyor will also check the bearing surface and wear in way of bush*es$ and stern

gland.

#.;.' Renewal9Repairs of liners

3racks, wear

-ully penetrating cracks always imply renewal of damaged part of liner.

-issures can be machined down provided that linerLs thickness remains within the limits

given below for wear, otherwise the damaged part shall be renewed.

Caor wear means that liner is unlit for use: the maximum wear allowed being as follows"

• &6 ? of rule thickness in way of the bearing area.

• 6= ? of rule thickness in way of out the stern8gland.


24/24

These measurements shall be taken alter machining of corroded or ribbed areas of the

liner. Ahen damage *fissures or wear$ is important and requires the renewal of the liner,

the !urveyor shall proceed as for the liner of a new shaft.

The new liner or liner sections ordered shall be submitted to the !ocietys factory

inspection test *quality of material, hydraulic test$, and liner lit and good condition *no

defects$ shall be checked alter machining.

Ahen renewal of the liner is not necessary and it is difficult or impossible to change onlya section of it without removing the part of liner in good condition, it is often easier to

have the damaged part re8metallic.

!ome yards can replace the damaged liner portion by two hail shells fitted on to the shaft

and welded together longitudinally. 2ny such repair shall be submitted to Technical 4ffice

for approval.

#.;.5 Ri!!ing in way of the stern0gland

(ibbing requires the complete 8 or part renewal of the liner only if thickness inside of

grooves is inferior to hall the regulation thickness. Ahen ribbing is slight, however, i.e.

when depth of grooves is ' mm, liner shall be machined over the whole length in way of

aft stuffing box.

!light ribbing needs only to be filed down or smoothed away with emery cloth.

Documents

Procedure for Ship Propeller Renewal