Docking Survey

8/13/2019 Docking Survey

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DOCKING SURVEY

PrefaceThis document describes the general background of a "Docking Survey," which

has an important role in a classification survey, and is meant to be used as areference for surveyors before they carry out field inspections.This document was prepared by Ichiro Ishikawa, former Chief Surveyor, and isbased on the prereuisites described below.

1-1. Underwater inspection!n underwater inspection that replaces a docking or slipway inspection which iscarried out by a company approved by the ClassificationSociety. The bottomshell, rudder and propeller should be inspectedindirectly by observing the television images transmitted by an underwater cameraused by a diver.

Detection of abnormalities should fundamentally conform to the contents of thisdocument therefore,details of underwater inspection are not specially describedhere.

1-2.Method of repairing damage#arious types of damage, such as damage due to stranding and contact with thebottom shell, may be detected during a docking survey. Such damage is usuallyrepaired by the shipowner under insurance, but in this document details ofrepairing methods will not be described. These tems will be introduced in theseparate home page describing "Damage and $epair" in futuer.

1-3. PropellerThe propeller and propeller shaft are inspected at the same time as a bottominspection. %owever, shafts need not necessarily be inspected during a DockingSurvey because "&ropeller Shaft and Stern Tube Shaft Surveys" are independentfrom the Docking Survey under the responsibility of machinery surveyor but briefe'planation is entered in this document.

1-4. Anchor and Chain Cable!n inspection of the anchors and anchor chains is not a reuirement of a DockingSurvey these items fall under the purview of a Special Survey. %owever, as it is

customary to inspect these items during a Docking Survey, they are covered in thisdocument.

1-5. amages in !ottom('cept for defects that occur because of stranding and contact with ob)ects or thesea bed, defects in the bottom shell, such as deformation and corrosion almostnever occur une'pectedly they occur gradually over a long period. *ecause the


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most repairs to the bottom shell involve repairs to double bottom tanks, consideringthat the tank should be emptied and cleaned before starting repairs and hydrostatictests carried out after repairs, the period for repairs should be estimatedapro'imately. Therefore, the data below should be collected before performing abottom survey.

1-".#t$d% the histor% of the ship*efore carrying out an inspection, have a look the survey report file submittedtogether with the survey reuest application, and check the recommendations andthe precautionary items if any .!nd read old survey reports as far back as possible,at least until the previous bottom inspection. Dents in the bottom shell may beunder+ or over+estimated, or overlooked depending on the position to be inspected,increase or decrease in the intensity of light rays, and arrangement of blocks.Dents that have not appeared in reports in the last few years, may have beenreported already in the past. There have been instances

1-&.'or(ing #ched$leThe schedule for docking , undocking and sailing dates are determined by theshipowners sailing schedule and the shipyards docking schedule therefore, theseinformations should be obtained for reference. If the docking period is as short astwo or three days, both shipowner and shipyard are unlikely to carry out the bigrepairs to the bottom or side shell unless the shell is heavily damaged. The dockingperiod gives you an appro'imate idea of the e'tent of the bottom shell works that islikely to be carried out. Information such as the time the ship will bedocked-undocked , how many hours does it take the dock will be dry, and capacityof discharge pumps of the dock should be obtained for reference.

1-).Marine cas$alties!fter the previous docking, instances where the ship hits the uay, or the bottomshell came in contact with the sea bed or floating ob)ects, should be correctlyentered in the log book. It is recommended to ask the superintendent or the asterabout the instances of marine casualties before starting inspection . If there areany report of bottom contact, the bottom inspection should be carried out withspecial care sometimes , In this case the ma)or repairs to the bottom shell may benecessary. !nother method of collecting data is to be reuest shipyard supervisorto show the specifications for repairs carried out to the ship, if possible.


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&hoto /+/ 01CC in Dry Dock2ne of the world largest ship, &iere 3uillaumat in 1IS4!#( argueira 5ard in

/678 Dimensions 1pp 9:/./: ' * ;


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*efore /6;9 the docking survey was reuested every year, becauseat the!nnual survey, docking was reuested. Some shipowners put their ships twice inthe year. *ut now the docking is only >timesin =years. The reasonof this

rela'ation was the improvement of paint. !t that time the effectiveness of paintscontinued only one year or less. If the ship was not docked for more than one year,the paint would peel off and alrae and shellfishes would stick to the hullunder thewater line, resulting in a drop of the ships speed . Aor the shipowners at that timedecreased speed was bigger problem than the e'pence of docking.

3. +he #$r*e% ,tem*ottom survey should be carried out after the bottom shell is cleaned after removalof the barnacles ,algae and shell+fishes and with the bottom shell is in the dry

condition. %owever when the dmamge to the bottom is suspected after anyaccident in the previous sailing, It should be inspected immediately after the waterin dock is discharged, then, the repair methods and the scope of repair should bedecided as soon as possible. the scratch or small indents in the bottom shell arere+inspected after the bottom shell is dry and cleaned.

/ Side and bottom shell> *ilge keel


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4. +%pe of r% oc(To inspect the bottom of a ship, the ship may be transferred to land or the bottommay be inspected through images on T# screens transmitted from underwatercameras used by divers. 0nderwater inspection entails various conditions all parts

of the bottoms of large ships with lengths and breadths in the order of >:: m and


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1IS4!#( argueira 5ard in &ortugal in /678

?ooden DockTodd Shipyard in *rooklin 4ew 5ork, /6;=E

9+< Aloating DockThis is a pontoon with length and width suitable for accommodating a specific si@eof ship. The pontoon is immersed into the sea deeper than the ships draft, and the


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ship is transferred to the pontoon the ballast in the pontoon is discharged so thatthe pontoon rises to the surface together with the ship on the pontoon. Dependingon the construction, there are three types of floating dock as shown below. The 1+type floating dock is not popular.

1+type

&ontton Type

The bottomonsists ofseveralpontoon.


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!STIC!4Ship 5ardin 3ranCanaria,Spain /67=

Ship on thetraverserwhichshifts right

or left.


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Cyncro+liftwinch

5. #afet% in oc(&oints for ensuring safety during inspection are listed in the other "3uidelines for&reventing !ccidents for Surveyors." Some of these points are repeated here toemphasi@e the precautions and to ensure that you do not suffer from an accidentsduring inspection.

/ (nter the dock only after the water has been completely pumped out and afterconfirming safety. If you enter the dock when almost all the water has been

pumped out, there is a chance that the sea water might gush back temporarily ifdirt or plastics etc. have clogged the pump strainer for filtering dirt this isdangerous because the sea water might gush into the dock with tremendouspressure and force.

> ?atch carefully for ob)ects falling from above when you are close to the sideshell or close to the dock wall. !n instance has been reported in which a lifeboatfell on a surveyor inspecting a ship, causing immediate death.


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barnacles using a high pressure water )et is widely used. Direct impact of this highpressure water )et on the body is dangerous. you shout reuesting the )et to beturned off.

Cleaning with highpressure water )et

; ?hile lowering the anchor and chain cable, sometimes they slip off suddenly.


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&hoto ;.> 5ou should be carefull under the anchor and chain cable.

&oto ;.< Staging?hilethe stagings are erecting around the rudder or propeller, sometimesstaging board is not yet binded. During erecting staging we should be careful.

8 In the floating dock there are no hand rails on both ends.


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6 Suspded stage

". Proced$re for !ottom #$r*e%Similar to other inspections, a bottom survey is a kind of visual inspection.Tools used during a bottom srvey are a test hammer, light, measuring tape, and astretched string for measuring the depth of dents. ! large hole or indent in bottomshell can be detected easily by anybody, but it is very difficult tofind any small indent or cracks while walking around the dock. The bottom area ofthe worlds largest tanker, "5ahre #iking," has an area of appro'imately


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still wet and uncleaned, we should inspect damage as soon as possible to deciderepair method and e'tent. In this case the bottom should be inspected again afterthe shell plate is dry and cleaned.

".2 ,nspection before Painting

Shell plating is to be inspected before re+ painting. *ecause in a wet paintedcondition we cannot detect fine cracks. If you refuse bottom inspection on holidaysor weekends, and carry out the inspection on the following working day, there is apossibility that painting will have already commenced and small cracks will becovered with paint.

".3 #%mmetrical amination4otwithstanding the bottom survey, the hull structure is generally symmetricalabout the centreline. ?ith the e'ception of local damage, such as dents due tocontact and cracks, if we find a crack on the starboard side of the hull, there is ahigh probability of finding a similar crack on the port side at the same location,although there are e'ceptions to this case. ?e need to check both port andstarboard sides paying attention to both sides.

".4 irt% #pots2n both bottom and side shells, if we find spots that are dirtier than thesurroundings, there is a possibility of a flaw in the vicinity. The area where the painthas peeled off due to abrasion must be carefully e'amined.3enerally, such an area will be badly corroded.

".5 'et 0ocationsIf we find partly wet spots in a dry shell area, small cracks may be concealed. !ftercleaning the shell plate, sometimes algae or barnacles remain at wet areas. Suchlocations often develop cracks. Arom this point of view, the bottom inspectionshould be carried out when the shell is completely dry.

"." ow to etect ents1arge local dents can be easily detected but it is easy to overlook a dent thate'tends over a wide area. In particular, dents in the curved shell plate in the bilge,fore and aft peak parts are difficult to identify. If the side shell plate is vieweddirectly from the dock side, dents can be overlooked easilybecause of the effect of light rays striking the plate at this area. There was aninstance of a large dent being detected in the side shell plate after all inspectionsand repairs were completed and the ship was )ust about to sail.

1/ #ide shell plateIf the side shell plate is inspected by looking at it from various angles or by lookingup from the dock , dents can be detected easily. 1ocations that are suspect may beobserved later by looking down and inspecting the shell plate from the deck. ! dentin the plate can be overlooked if the shell plate is e'amined from position !. The


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plate must also be viewed from position * to check for dents.

! dent in the plate can be overlooked if the shell plate is e'amined from position"!". The plate must also be viewed from position "*" .%ave a look the side shell plate in the vertical and fore+aft directions.

2/ !ottom shellSmall dents in the bottom shell plate can be detected easily if we bend our waistand look backwards to view the bottom shell between legs, thereby lowering yourline of vision. ?hen the beam of light is pro)ected parallel to the bottom, a dent, if

present, can be detected as it will appear dark. %owever, in a ship of rivetedconstruction, the lapped parts of the bottom shell appear shaded and are likely tobe mistaken for dents.If we find a clearance between the keel block and the keel, a dent is likely to e'istin the keel.?hen the big and widly repairs works to the bottom are carried out , in the ne'tdocking widly dent may appear in the same area.

In case the floating dock , the dock itself may deform as the same as bottom. Inthis case a clearance between keel blok and keel may not be appeared.


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Aig.;./ ('aminationof *ottom Shell /1ower our line of vision, If we inspect the side shell by looking down from thedeck,we can easily detect dents .

Aig. ;.> ('amination of *ottom Shell >point the light parallel to the shel l

".& Meas$ring and ecording of entsIf the dent is minor and repair is not necessary at that time , it may be recorded inthe survey report without outstanding recommendation. !t the ne't docking survey

the same atra should be re+ measured. if the si@e of the dent is increased, repairsshould be recommended.

".&.1 ow to Meas$re entseasurement using a stretched string is easier. 0se two magnets for securing bothends of the string to the bottom shell, and measure the dent using a scale. Thismeasure+ment can be performed single+hand. The measurement using transit isalso useful,


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".&.2 Preca$tions d$ring Meas$rement*ecause the measurement is to be carried out to determine whether a dent hasincreased in depth by measuring the same location again during the ne't docking,care should be taken to record the measurement points and the reference pointsfor measurements correctly, so that the dent can be measured at the same locationand compared to the previous measurement. !s shown in the figure below, ! andC are taken as reference points, and the depth of the dent is recorded as &$.During the ne't measurement, if ! and * are taken as reference points and thedepth of the dent is taken as &, it indicates that the dent has reduced. The fwd+aftposition and position in the breadth direction of the reference points should berecorded for future reference, as shown in the figure below. The reference pointsshould preferably be taken at bulkheads or other locations where movement isconsidered to be minimal. In the case of a double bottom, record whether the tankis empty or full during the measurement.

Aig.;.9 Deformation of bottom shell


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Aig.;.= easurement of Dent /

Aig.;.; easurement of Dent

".) !end in !ilge eel!lthough no reuirements for bilge keels are prescribed in classification rules, ifbilge keels are fitted, they should be inspected. *ilge keels might bend because ofcontact with the sea bed or contact with floating ob)ects.


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If we view the bilge keel from end to end, we can easily detect a bend.

Aig. ;.7Damage in bilge keel

".6 amage to ,nternal Members(ven a minor dent of bottom shell plating it may accompany a damage of internalmembers such as frame, bulkhead or floor. In this case not onlye'ternal inspection in the dock but also internal inspection in that tank orhold should be reuested.If a minor dent is located in the fuel oil tank, the remaining fuel oil must be shiftedto other tanks to carry out the internal inspection. In winter,sometimes transferring fuel oil is very difficult because of its low viscosity, so weshould negotiate with the shipownwers to carry out the internal inspection at thene't docking depends on the condition of damage.

&hoto.;./Slight Dent


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&hoto. ;.>Inside the Double *ottom Tank in !rea fo a slight Dent

".17 #hell Plate +erminolog% and #hell pansionPlan$efer to the Shell ('pansion &lan when we want to check the si@e, type andthickness of a shell plate in which damage has occurred. The Shell ('pansion &lanshows the bottom shell and side shell on one sheet of drawing with a /B> scale forunits in the longitudinal and transverse vertical directions. That is, if the scale inthe length direction is /B/::, the scale in the width direction is /B=:. In addition toshell data, the positions of holds and tanks, frame spacing and dimensions of allframes are also shown in this drawing. &lates on the shell are named as followsBF for keel plate plates ad)acent to the keel starting from the garboard strake are

named seuentially as !, *, C, D, (, A, 3, %, H, 1 not F as "F" is used for the keelplate not "I" as it is likely to be misunderstood for some other symbol. Thetopmost strake sheer strake is named S using the initial letter of sheer strake.Aor the same strake say %+strake, the plates are numbered /, >,


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and bulkheads that fall on the side shell are indicated by broken lines the framesare indicated by single dot and dash lines. The number above mark is the platethickness to distinguish it from other values. Class D, Class (, etc. indicating thekinds of stee,such as D class steel etc. The mark J shows a )oint in the breadthdirection of the plate a long S shows a )oint in the length direction or a block )oint.

Aig.;.8 Shell ('pansion / Aig ;.6 Shell e'pansion


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Aig.;./: Shell ('pansion


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&artly renewB 2nly deformed part

$enew B all plate renew

Aig.;+// $epair symbol mark

Aig.;+/> ('ample of repair mark

S+/= $enew ,S+/;&artly renew4+/= and 4+/;BAair in place,S+/= >; ( means B >; is the thickness of plate and ( is the grade ofsteel. (+grade steel, * is *+grade steel"-12 ow to Predict efecti*e 0ocationsIf defects such as dents are found in the side shell plate or the bottom plate, thelocation of the part where the defect has occurred should be recorded. %owever, ahold or tank with a dent cannot be identified from the outside. This has to be

)udged later by observing the Shell ('pansion &lan, but the methods described

below may be used to confirm the appro'imateposition of the defect.


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Aig.;./> Identification of hold from outside mast or bottom plugI/ Hudging the position of dent by the mast or crane postIf the dock is wide, move the dock side so thatwe can see the mast or crane poston the deck. These are usually installed on a bulkhead. Aor instance, you can

)udge whether the dent is between 4o. > %old and the 4o. < %old. %owever, if thewidth of the ship covers almost the entire width of the dock, this method cannot beapplied.> Hudging the position of the dent looking for the bottom plugs In double bottomtanks, bottom plugs are installed at the aft end of the tanks near the centreline of

the ship for draining residual bilge in the tanks when the ship is docked. Theseplugs are coveredwith cement therefore, if you observe a raised part similar to asmall dish, it is a bottom plug. Arom the bottom plugs, you can aee theappro'imate position of the aft end of each tank and estimate the position of thedamage.


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Aig. ;./< Identification of double bottom tank

&. Co$rse in oc(There is no specific procedure for inspecting the hull under the water line for shipsof a specific si@e and an arrangements of keel blocks however ,the followings arean e'ample of a course for walking around the dock and inspecting the bottomdamage so that defects are not overlooked.Docks are usually perpendicular to the coast +line. The customary practice is tostart from bow and walk towards the stern on & or S sideThis is the procedure recommended .

4umbers in the circle corresponds to the followings.Aig. 7./ course of Docking Survey


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CheckEpoints at each position are as followsB/ 8ront *iew/ ! bend in the stem by comparing the port and starboard sides, or a bend due tocontact of the stem with some ob)ect can be detected only when viewing the shipfrom the front.

> Dents in the shell plate at the bow and corrosion due to the anchor chainrubbing !rea of shell chafed by chainCarefully observe corrosion due to chafing with chain . 0se a ladder for inspection,if necessary. Corrosion mainly occurs in the hatched areas shown in the figurebelow instances of grooved corrosion have been freuently observed. If corrosionis severe, these area should be gouge the welded beads and re+weld. If the ship isto operate in coastal water routes and is likely to anchor freuently, a half+roundsteel bar fitted near to the seam will prevent chafing of the welded beads.

Aig.7.> Aront #iew Aig.7.< !rea caffled by chain cable


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between keel and blockl, the forward bottom may be lifted or the top surface of keelblock is not correct.3/ 8orward bottom/ Carefully Inspect for dents that might occur in the keel or ! strake because ofpanting.

&hoto.7./ 1ifting forward bottom

Aig.7.= !nchor position / Aig.7.; Damage due to anchor pea


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&hoto. 7.> !nchor position >Aluke end does not contact to the shell plate

Aig. 7.7 Chafed welded beads!. Chain rubs against the shell plate and peels off paint on the welded beads


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*. The portion of the beads where paint has peeled off and sub)ected to becorroded.C. Corrosion progerssesD. !ppearance of grooved corrosion

&hoto. 7.8 %alf round bar protects the corrosion of welded beads

> ?atch the area between keel blocks where the keel plate will be corroded.*ecause during previous drydocking top of blocks ware not paintedThe welded )oints of the keel are likely to corrode easily.

4/ !ilge (eel fore end!ftre walking under the bottom shell, go to the sip side, and look through the allbilge keel from fore end to the aft end. ?e can easily find out the deformationof bige keel .

/ Simultaneously check the fore end of the bilge keel. Sometimes the crackappears at the fore end. (nsure that the crack if it e'ists does not e'tend to thebige strske. !lso check for corrosion, because corrosion freuently occurs at thefront of the bilge keel.

> Inspect the side shell in this area.

Sometimes the crack of bilge keel propagates to the side shell.


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body are listed below.

/ Condition of shell amidships?hen the ship has the side ports, as in a refrigerated cargo ship, check at the fourcorners carefully. Cracks happen at the corner because of shearing force.

> Check the freeboard mark, The mark might have been disappered or theremight be a mistake in the characters. !lso check the draft marks.

Aig 7+8 Side Shell to be carefully e'amined.

Aig. 8.7 Corrosion of *ilge strake


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9 Inspect the deck scupper opening.

= (ngine room areaIn case of the ship with midship engine, the followings are to be e'amined.

/Sometimes crack appears at the corner of sea chest and valves.These items are carefully e'amine after erecting of stagings and cleaned.and also look into the inside of the distance peaces.> Corrosion often appears in the shel plate behind the boiler blow +off opening.

"/ and &/ 9bli:$e stern part1/Aft end of bilge (eeelthe same as 92/ #hell plateInspect the shell in the aft region. The thickness of the shell plate in this region isless than the midship region. In aged ships samall holes appearesbecause ofwear and tear.3/ ngine room&lease refer to idship part.

8 #tern part4ot only hull constructio we have to e'amine the rudder and propeller.// +he clearance between the (eel bloc(s and the (eel e'amine the clearance carefully. The stern frame might be raised because ofhitting the bottom or impact with other ob)ects. Details of the stern frame damageand repair works will be introduced in the other home page in future.2/ Propeller and r$dder

!lthough the propeller falls under the responsibility of the achinery Surveyor, butthe %ull Surveyor has to inspect the propeller during bottom survey. The achinerySurveyor starts his inspection after the sea chest cover is removed and staginghave been erected around the propel for inspection. Thus the inspection by theachinery Surveyor might be a few days later than the inspection by %ullSurveyor. a)or damage to the propeller blade or the guard ring can be easilydetected observe the conditions of the propeller and guard ring and if we findabnormalities, report them to the achinery Surveyor after the *ottom Survey.*ecause the date of undocking of a ship is fi'ed, if repairs to the propeller arereuired, they should be carried out at an early stage.The following points including propeller should be e'amined.

/ Is the shoe piece raised E> Is there an abnormality in the stern frame E


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Aig.7+6 Check point for stern part

6Aft ;iewInspect the stern and the rudder from this position./ ?hether the rudder is amidship position E> Is the rudder centred E


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). #hell efects). #hell Plating

!t the renewal of the cracked or weared out plates, it is necessary to see the "Shell('pansion &lan" . *ecause there are many kind of steel plate such as mild stee

platel, hightensile steel plate etc. !mong them there are many kind of steel such as!+grade, *+grade,C+grade etc. ?hen renew the shell plate, the same steelshould be used.

Typical defects found in the bottom and the side shell are as follows.).1 !ottom #hell1/ !ottom scratches and entsost damage to the bottom shell is due to contact with ob)ects on the seabed.*ottom scratches are slight damages. Such damage happens when the shipoperates in shallow waters such as the ississippi river, near the coastline, etc. Inmany instances, bottom damage due to contact starts from the forward part and

disappears around midship.*ecause of scratches, the bottom paint has peeled off and corrosion occurs. In thiscase, remaining paint and rust should be cleaned by shot blasting and properly re+painted . ?hen the bottom has had contact with a coral reef or rocky seabed, largedents and-or holes appear with scratches. In this case, as a matter of fact,fractured shell plate should be cropped and renewed with damaged internalmembers. If the dents are relatively small, they may be left as they are with someeffective internal reinforcement.If we find a large fractured opening during the bottom inspection, naturally weshould recommend repairs. %owever, there have been many instances where theshipowner has believed that there were no abnormalities and dents were found

during the bottom inspection, which naturally gives the shipowner a headache. Theshipowner usually decided sailing schedule beforehand, they hate prolongingdocking period because of ma)or repairs, they persists in putting off ma)or repairs,and try to carry out simple repairs within the drydocking period. That is why sparksusually fly between the Surveyor and the shipowners representative.$egardless of e'perience of bottom inspection, the surveyor always feels uneasybefore docking survey.

Aig.8+/ Damage in bottom shell


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2/ ents d$e to panting?hen the ship sails in rough weather without reducing speed, dents might occur inthe keel and ! strake starting from the fore peak tank to the middle part of 4o./?ater *allast Tank , because of the relation between ship speed and curvature ofthe forward bottom. In the worst case, the floors in the tank and bottom stiffeners

buckled.4aturally, the Surveyor should recommend repairs to the shell, as well as theinternal members.

3/ Corrosion of (eel and ad


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Aig.8+> Cracks in Sea Chest

&hoto 8./ Corrosion of Feel and ! strake in way of forward bottom


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&hoto. 8.> Ship with Aalse Feel?hen the ship with a fales keelis seated on the ordinary keel blocks, fales keel and

center girder may be heavily damaged.

i&hoto. 8+


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&hoto 8+9 *ig damage in bottom >*ig damage can be detected by anybody

&hoto 8+= Slight Dent! slight dent in a curved plate is difficult to detect


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&hoto 8+; Corrosion of welded *ead /Corrosion in a welded bead of a bottom shell plate looks like a crack, but is not acrack. !s shown in the macro etching, this corrosion appears in a heat+affected@one.


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&hoto 8.7 Corrosion of *eads > acro (tching

&hoto 8+8 $eed Screen *ottom &late CorrosionStress corrosion due to buckling in the midship region of the bottom plate in atransversely+ framed construction the dent itself is small. $einforcement by fitting acarling inside the tank is recommended.


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6.2 !ilge eelIn large tankers with the midship coefficient approaching /.:, the bilge keel maynot be fitted when the ship is newly built. If bilge keels have not been provided onboth sides during the bottom inspection, check whether the ship had no bilge keelswhen the ship was constructed or whether they have been ripped off during a

marine casualty. If there are traces of welded beads on the bilge strake, we mayconclude that the bilge keels have been ripped off during a marine casualty.Damage to the bilge keel is as follows/ *ilge keel dropped off, a part of bilge keel ripped off, kinks in bilge keelThe bilge keel is a member that does not need to conform to classification societyrules. %owever, if it is damaged, it is normal to repair the bilge keel, usually underinsurance.

> Cracks at ends!ged ships which constructed with rivet not weld. $ivets at the ends of the bilgekeels often worked loose. In a welded ship, the welds at the both ends areprovided with large leg lengths, but sometimes cracks are found at the ends.


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&hoto 8+6 Drformationof bilge keel

&hoto 8./: Corrosion of the *ilge Strake above the bilge keel

The bilge keel is not directly welded to the shell it is generally connected to theshell through a flat bar. If it is welded directly to the shell, there is a strongpossibility that cracks might develop in the bilge strake when the bilge keel suffersdamage.


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Aig. 8+< ('ample of *ilge Feel

Aig. 8+9 Crack at *ilge Feel (nd /

Aig. 8.= Crack at *ilge Feel (nd and )oint of bilge keelCracks tat the )oints of the bilge keel might develop, causing cracks in the bilgestrake.

Aig. 8+; ('ample of *o'+type *ilge Feel


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).3 #ide shellThe followings are the e'ample of the defects in the side shell./ Corrosion> Dents and fracture due to contact with uays or floating ob)ects


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in car carriersand ships operating in narrow waterways, such as the St. 1awrencewaterway are also observed to have dents at these area.

> Aore and aft body near the waterlineDents appear in these area when the ship is pushed by a powerful tug boat while

berthing.

+>

; 4ear the hatch openingsIn ships that load-unload cargo from-to barges, dents are often caused when thebarge or the cargo comes into contact with the ship.

7 &ropeller and rudderThe propeller and rudder might hit floating ob)ects, get fouled in fishing nets,propeller blades might be bent, guard ring might fall off, and the portable bo' forthe rudder sometimes drops off.8 *ilge keelInstances have been reported of a part of or the entire bilge keel dropping off aftera ship hit a floating ob)ect. The dmage of the bilge keel have been observedfreuently. Carefully check the deformation of billge keel lookimg throughfromfore end to aft end.

3/ Crac(sCracks in the shell plate mostly develop from cracks of the internal members andthey spread to the shell plate. Cracks might occur in the transverse or longitudinaldirection some cracks appears in the shape of a star.

1/ Aft end of collision b$l(head! large number of internal members, such as frames and stringers, are provided ina relatively small area of the fore peak tank. It means that the fore peak tank is arigid constructioncollision. ?hile the hold ad)acent to the fore peak tank is a large,broad space with a small numbers of internal members per unit volume. oreover,this region is often sub)ect to large wave impacts, which cause cracks in 4o. /hold.


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!s the reinforcement against panting, classification rules reuest side stringers orbrackets in the region between the collision bulkhead and :./=1 from the bow. *utat the end of these members crack appears and develop to the side shell.Therefore, the vicinity of the ends of these members should be carefully inspected .Initial cracks appear in the vertical direction and have a length of =: mm to /::

mm.


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Aig.8+6 ('tension of internal crack to shell plate /

Aig. 8+/: ('tension of internal cracks to shell plate >


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Aig.8+// Crack near the bulkhead

3/ !ilge (eel #ee #ection 6.2.

4/ =5/ Crac(s in the sheer stra(e at the ends of s$perstr$ct$resCracks sometimes appear at the sheer strake at the fore and aft ends of thesuperstructure *ridge of "Three Islander" ship and long &oop or long Acle shipsbecause of hoging and sagging.Sheer strake at the break of the superstructure should be carefully e'amined

Aig.8./> Crack at the sheer strake.

"/ #hell plate in wa% of the the aft pea( tan(In ships with a long aft peak tank such as ocean tugs boats or some car carriers,aft peak above the rudder is flat and wide. sometimes crack because of sternvibration appears in the !&T and may propagate to shell plate. Care should be


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taken.

&/ !ilge partCracks at the lower ends of frames in cargo holds sometimes e'tend to the shellplate. Cracks in the shell plate appear in the hori@ontal direction

.)/ ;icinit% of b$l(headsCracks may also occur in the vertical direction along the bulkhead due to thedifference in rigidity of the frame and the bulkhead. these cracks propagete toshell plate. This situation is shown in the figures below. Shell plate In the vicinity ofbulkhead should be carefully e'amined not only outside but in the hold side.especially in aged ships6/ Crac( in r$dder plate > &lease refer to the $udder section.

4/ CorrosionThe shell plate is generally painted when the ship is in drydock but in the hold it isnot well painted. In the following area shell plate is thinner than other area. Ifnecessary the tickness should be measured in aged ships. 1ocations to bechecked carefully are shown in the figure below.

Aig.8+/< Corrosion from inside4umber in the circle corresponds th he folowings..1/ Chain loc(er bottom#entilation of the chain locker is not enough and bilge water accumulates in thebottom, resulting in the rapid onset of corrosion. In large ships, the chain locker isisolated from the shell plate, corrosion does not appear in the shell plate. %owever,in hte normal ships, the shell plate forms a part of the chain locker, side shell platecorresponding to chain locker bottom shoul be carefully e'amined.


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Aig. 8+/9 Chain locker bottom

2/ +an( topCorrosion at the sides of the tank top plate proceeds faster than other area, but it isnot faster than in chain locker. If corrosion at the sides of the tank top plate in theaged ships is neglected, it e'tends to the shell plate and sometimes it leads tocorroded openings appear in the shell plate. In ships where the sides are raised,such as bulk carriers, this problem does not occur.3/ Aft end of ?tween dec(In ships with a tween deck, bilge water generally accumulates at the aft end of thedeck and causes corrosion that e'tends to the shell plate. This is not a ma)orproblem, e'cept in aged ships.4/ @ear the forecastle aft b$l(head*ilge water in the forecastle accumulates at the aft end on both side. Therefore,forecastle end wall on both lowest corners to be carefully e@amined .5/ Corrosion below side sc$ttlesStarting with Special Survey 4o. >, it is mandatory to measure the thickness of theshell plate below side scuttles. $ules prescribe inspections of the condition of theshell plate below side scuttles after removing the lining during Special Survey 4o.


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the surrounding shell plate. If rusting is e'cessive, enter the cabin after completionof the bottom inspection and ask to remove the lining and e'amine the state ofcorrosion in the superstructure side plate.

$ef. The Classification $ules In the Special Survey 4:.< reuest as follows B "The

lining in way of the side scuttles is to be removed as reuired by the surveyor, andthe shell plating should be e'amined."

Aig.8+/= &ay attention to the area below the side scuttles


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&hoto 6.//!ttention to the lower area of side scuttle

"/ 8orward and aft of b$l(heads #ee )/7 0pper edge of bilge strakeSee = of Section 6.> for e'ternal corrosionof the bilge strake.,Section4o.

#tern 8rame('cept the rudder bearing, the propeller shaft and the boss, stern frames in mostships today are fabricated from steel plates. It is called as built up stern frame.In the past, they were made of cast steel however, due to the complicated shapeof the stern frame, casting and heat treatment were difficult, blow holes weresometimes detected at the connection of propeller post and shoe piece, andrepairs were not easy. These problems do not e'ist today. Serious damage doesnot appear in the stern frame unless the ship is stranded or the stern frame hits anob)ects in the bottom. The stern frame today is hte most safe member of the ship.%owever, recently it is not totally free from any damages. Sometimes crack isrepotred in the ariner type stern frame. !t the connection of rudder horn to sternshell plate the cracks are reported.

The figures below show e'amples of the construction of stern frames.


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Aig.6+/ 2+type Stern Arame

&ractically we can not see in these days.This type has a propeller post on the foreside and a rudder post aft side with severalgudgeons.In large ships both posts were rivetted.

fig.6+> 3+type Stern Arame

0ntill around /6;=, stern frameswere mostly made of cast steel. Theywere )ointed to the shellplate by rivetting or welding.


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Aig.6+< C+type stern frame Inthese days stern frames aremostlyfablicated from steelplate. This is C+type SternArame for a small ships. Inother word it is called a built upstern frame.

Aig.6+9 ariner type Stern ArameAig.6+= ariner typt Stern Arame&erspective

6.1 #tern 8rame amage


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Damage to stern frame has two typesB minor damage is the cracks and slightbends in the shoe piece and big damage is fracture, twist, and bending of shoepiece due to stranding or touching bottom.

17.2 ow to find the defects in #tern 8rameIf the clearance between rudder and shoe piece is less than the reuired distancein the drawing, for instance >=mm=mm or


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Aig.6+7 Clearances between rudder and shoe piece >If the value c and d are different, the shoe piece is twisted.

Kinc anodes for preventing corrosion are fitted to the stern frame and the rudder.Steel members in the vicinity of the stern frame are likely to corrode because thepropeller, which is located nearby, is made of copper alloy. If @inc anodes arefitted, they corrode instead of the steel members. !lthough @inc anodes are not a

rule reuirement, but if they are worn out, replacement with new @inc anodesshould be recommended.

6.3 Minor amege1/ #hoe piece and propeller post Connecting brac(et

! thick bracket is generally fitted connecting propeller post and shoe piece. If acrack is found in this bracket, replacement of bracekt rather than re+welding isrecommended, depending on the si@e of the crack.


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Aig.6+8 Crack in bracket

2/ $dder horn connectionIn mariner type stern frame rudder horn is )ust hanging from stern. thereforeSometimes cracks appear at upper end. These cracks occur at the welding part ofthicker horn plate to thinner shinner stern shell plate. These welding isa little difficult. The cause of cracks seem the defective welding at the new building.


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Aig.6+6 Crack at the rudder horn

Aig.6+/: ('ample of crack at the section !+!(ither the defective weld should be repaired by re+welding it after adeuit edgepreparation or the structure should be reinforced if there is a structual discontinuity.

Aig.6+// ('ample of crack at the section *+*3/ Crac( in slot weld of shoe pieceSimilar to the rudder, cracks sometimes appear at the slot welds of the cover plateof the shoe piece and water enters into the shoe piece. (ven if water enters intothe shoe, the plate is very thick and the internal corrosion is not big problem,%owever, it is better to re+welded after discharging of water in the shoe piece.


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&hoto. 6+/ Crack of slot weld in the bottom of shoe piece

6.9 a)or Damage due to Strandinga)or damage to the stern frame includes the damage due to stranding andtouching the bottom ma)or damage is very rare with a probability of appro'imately:.>L, or / in =:: ships. !lthough many ships are stranded or suffer from touchingwith the bottom, the damage generally occurs in the double bottom but infortunallyat the same time the lower part of stern frame such as shoe piece suffers the bigdamage.The e'ample of big damage of shoe is as

followsB in this case lboth rudder and propeller are also damaged.


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&hoto.6+> Damage to built up stern frameTwo dimensions shoe piece is bent and twist, The shoe piece is offset tostarboard by


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&hoto.6+< Damage of stern framethree dimensional damageShoe piece is bent to the starboard side by 8:mm, lifted by >:=mm andtwisted counter+clockwise by /= degrees.

1/ !rea(ing of shoe pieceIf the shoe piece breaks, a new shoe piece can be manufactured and re+fitted.?hile repairing, it means welding or local heating, displacements in the vertical,longitudinal and transverse directions ans also twisting should always be measuredwhile. the gudgeon hole should be bored on site.

2/ !ending of shoe pieceIf the shoe piece bends in the vertical and transverse directions, the bend is athree+dimensional bend. 4aturally, some damage would also have occurred to therudder. Depending on the e'tent of damage, the bend should be heated by setting

up aprovisional heating furnace around the bent shoe piece, and the shoe piecefaired by using oil )ack . !fter fairing up the shoe piece, the center of rudder shouldbe re+aligned. In some cases, the pintle si@e might need to be increased, thegudgeon hole filled up by welding, and re+boring carried out. Temperature controlwhen fairing the bend is difficult. This work should be performed by a shipyardse'perienced in such work. If e'cessive bending has occurred, it is easier to cut thebent portion and replace it with a new shoe piece.3/ +wisting of shoe piece


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The twist in the shoe piece might be local or e'tend over the entire length of theshoe piece. Aairing a twist is very difficult. %owever, depending on the e'tent ofdamage, the twist can be faired by a similar procedure as the shoe piece. If thetwist is minor, and the gudgeon thickness allows, It can be repaired by re+boring ofgudgeon and fitting a thicker new bush

Aig.6+/> !d)ustment of rudder center/ If the thickness of the gudgeon is greater than If the bend is such that the thickness mentioned above cannot be obtained,

filling can be carried out by welding, followed by boring.


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Aig.6+/< Aair in place of shoe piece >$epair work of the shoe piese which lifted >:=mm upwards

&hoto.6+9 Aair in place of heavily damaged shoe piece


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Aig.6+/9 Aair in place of shoe pieceThe furnace is under the propeller boss. 2n the S+side there are oil )acks and onthe &+side there is a strong support between dock wall and the fore end of the shoepiece. The heat treatment after the repair work is most important. This repair workwas carried out at the !(S!, 2laveaga, Spain.

17. $dderThe rudder is the most important part of the ship. If the rudder becomes defective,the ship can no longer operate, even though the condition of the hull andmachinery is satisfactory. Similar to the propeller, the rudder is normally immersedunder water, therefore, details of its condition can be observed only during abottom inspection when the ship is docked. Inspection of the rudder also includesinspection of deformation, checking for cracks and the condition of rudder bearingwear down.17-1 +%pe of r$dderThere are many types in rudder. The followings are the typical e'amples .


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Aig./:+/ hanging ridder Aig./:+> Symple' rudder

Aig./:+< $udder with one pintle Aig./:+9 ariner rudder


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Aig./:+= T+Type rudder with > pintles Aig./:+; ariner rudder with > pintles,

Colt no@@le rudder !ctive rudder


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Aig./:+= 2ld type $udder with many pintles Single plate rudder

Santa aria Cutty Sark /


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Cutty Sark > 4elsons AlagShip#ICT2$5

Alap rudder , Aig. missingAig.//+; Special rudders Aig. missing

17.2 0ifting and emo*ing $dder!t first the rudder bearing clearance *etween inner diameter of bush and rudderstock or pintle should be measured when inspecting the condition of the bearing. Ifan abnormality is found, the rudder should be lifted or removed, depending on itsconstruction. In conventional rudders with upper and lower pintles or lower pintle

only, the rudder has to be lifted. %owever, for a hanging rudder or a ariner typerudder, the rudder should be lowered for a Simple' rudder, the rudder post shouldbe removed. In any case, the tiller of the steering gear should be overhauled andremoved, in such a way that the rudder and steering gear should be disconnected,and the )umping stopper removed. !n e'ample of the seuence for lifting therudder is shown in Aig. /:+; If the rudder is lifted by a )ack, the )ack should bepositioned under the vertical frame of the rudder, otherwise it might dent thebottom plate of the rudder. If the seuence is not followed correctly, the ruddermight drop and break the shoe piece therefore, work should be carried out with


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much care.

/ Step /*efore lift > Step >


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connecting a casting in the rudder and the rudder plate. cf. Aig. /:+7


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Aig./:+7 $udder partly lost

If the cracks is found in the hori@ontal direction at the upper part of the rudder ,carefully check the cracks after the stagings are erected.

17.4 $dder #toc( 8ail$re$udder stock failure is very rare, but in the past, there was an incident when awhale in a dying condition hit the rudder of a whale catcher boat operating in the

!ntarctic 2cean, the rudder broke and dropped into the sea. 0nfortinately therudder was a hanging rudder without shoe piece.

Aig./:+8 %anging rudder will drop when rudder stock is broken

3enellary no such incidents have happened. *ut in /6;:, a tanker of


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&hoto./:+ *roken surface Aig./:+ Temporaly repair17-5 Crac( in r$dder plate/ !t the slot weldThe rudder plate and rudder frame can be welded directly on one side of the

rudder, but the cover plate on the other side can not weld directly.So these members are )oined by slot welding. If assembly accuracy is poor, slotwelding is incomplete and cracks occur. Conseuently, cracks appear in the rudderplate only on one side.

Crack appears

holo@ontally Cracl at the slot weld&hoto. /:+/ Crack in the rudder plate at the slot weld2/ !oth endsSometimes cracks are found at the front edge and-or aft end.


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#ertical crack at front endSuddenly ships speed dropped.

Crack appears at the end17.5.1 etecting ingress of water into r$dderIf we find some wet area in the rudder platet, it is likely that cracks have occurred inthe rudder plate and sea water has ingressed. (ven if water has entered into therudder, only the buoyancy of the rudder is lost and no ma)or casualty will occur.%owever, internal parts of the rudder might corrode, therefore, the plug in the

bottom plate of the rudder should be opened and water should be drained out. Ifwe strike the rudder plate with a test hammer, we can detect the ingress of waterfrom the sound. In large ships, the rudder is high above the dock floor if we cannotstrike it with a test hammer, pick up a stone or something in the dry dock and throwit agsinst the rudder. ?e can find the ingress of water from the sound made by thestone hitting the rudder.


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Aig./:+8 ('amination of Ingress of sea water throwing stone orsomething in the dry dock

17.5.2 Meas$res when crac(s are detected/ 2pen the plug at the bottom of rudder plate and drain the sea water from therudder.

> !fter close the plug fill the rudder with air to perform the air test and check thecracks.


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we may conclude that the portable bo' has been lost.

!fter removal for lifting rudder 2rdinaly &ortable bo'Aig./:+6 &rtable bo'

17-& PintleIf we consider the rudder is a hinged door, the pintle is analogous to the vertical pinin the door hinge. Conseuently, if the pin is damaged, the door cannot be openedor closed. Similarly, when the pintle damaged, the rudder loses its freedom ofmovement and the ship is unable to sail under its own power. !lthough the pintle isa small component, it plays a very important role. Depending on rudder type thereare one or two pintles in the rudder.

17-&-1 Pintle constr$ctionThe bearing surface of pintle is covered with a copper alloy sleeve. !fter a taperedpart as shown in Aig. /:+/:, the end of the pintle has threads cut into it. The pintleis secured with a nut. If the nut loosens and comes off, the pintle will droptherefore, the nut is kept with nut stopper.The shrink+fitted sleeve is only cylinder or with bottom. In small ships, a removableheel disk is often fitted to the bottom of the pintle this heel disk support the weight


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of the rudder.

Closed sleeve Cyrindorical sleeveAig./:+/: Construction of pintle

17-&-2 amage to pintle*ecause the pintle is short, it does not bend. The damages to the pintle are asfollows./ Aracture> Sleeve drops off


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Aig./:+// 4ut above 2rdinary rudder

?hen the nut is loose or lostand at the same time portable bo' is lost, pintle willfall down into the sea and also, if the nut secuing device is out of order,pintle

drops off. *ut this case is very rare. *ecause in almost case, the nut is fitted on thetop of the pintle.The nut securing device is provided with means to prevent it from working loose.During inspection, the securing device should be carefully checked.To prevent the nut from rotating, steel pieces are welded as shown in the Aig./:+/>. This welded nut stopper is not thick about =mm. ?hen the nut stopper ise'cessively corroded, the stopper should be renewed.Some ship has a split pin through the nut and pintle head. *ut pin is very thinand easily corroded. The split pin is not prefarable.In most case, the nut does not become loose but it should be checked by tapping itwith a test hammer .


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Aig./:+/> 4ut below ariner rudder(ven if the nut is heavely corroded or disappeared, the pintle does not drop off.

Aig./:+/< 4ut stopper /


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Aig./:+/9 4ut stopper >

Aig./:+/= Cement cover

Aor prevention from corrosion generally the nut is covered with cement.If the cement is defective, it should be renewed.


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2/ 'itho$t lifting the r$dder?ithout lifting the rudder,we can measure the clearance using a feeler gaugeinserting between the bush and the sleeve. The method of measuring clearancesusing a feeler gauge is shown in the Aig./:+/6.The measurement is the same as above ie. fore+aft and & and S side.*ut in this case we can not measure the clearance at the middle section.


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Aig./:+/8 Aeeler gauge

The feeler gauge is a collection of thin metal plates of various thickness.

easure from bottom easure from top

Aig./:+/6 easuring pintle clearance

Clearances in the longitudinal fore and aft and transverse directions & and Sshould be measured in the similar way as before mentioned.2-1/ 8alse clearance?hen measuring the pintle clearance using a feeler gauge, the measurement ofclearance at the end of the bush sometimes shows a smaller value while the actualvalue of the clearance is bigger. !s shown in Aig. /:.>: and >/, the end of thebush should be chipped off and the clearance should be measured accurately.


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Aig./:+>: Aales clearance

Aig./:+>/ ('ample of actual measurement


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1eft B 4ew bush

$ight B ?eared bush,2nly lower end is normal.

2-3/ #tandard Clearancei/ PintleAor a newly built ship, the standard clearance is /.= mm.Aor a ship in service, Maim$m allowable clearances between pintle and b$shis " mm.IA the actual clearance e'ceeeds ;mm, the bush should be renewed.

3/ @ec( bearingClearance in the neck bearing can be measured after the rudder is overhauled.0nless other wise the measurement is carried out using a feeler gauge.Thestandard clearance is 9.: mm, If the clearance e'ceeds =.:mm, the bush shouldbe replaced. !ctually the wear down of the neck bearing bush is smaller than thepintle.

4/ amination of the #$r*e% eport in pre*io$ss$r*e%If the clearance of the pintle is =.= mm, e'amine the past measurement results inthe survey report. Aor instance, if the clearance at the previous inspection was .= mm. Then the clearance in the ne't survey willbe increased up to 8.:mm. so the renewal of the bush should be stronglyrecommended.If the clearance is =.: mm in the previous survey, In this case the wearingis only :.=mm. renewal may be deferred until the ne't inspection. There are noclearly+defined standards for carrier+bearing clearances however,e'amples of pastmeasurements of various bearings are given below. The "" mark indicates thatbush renewal was recommended The "!" mark indicates that renewal wasdeferred until the ne't inspection.


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Aig./:+>


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Aig./:+>9Clearance of carrier bearing


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Aig./:+>= Intermediatebearing

17-&-5 'ear of b$shThe bearing cannot be oil lubricated because the pintle is always in the water.Conseuently, very hard wood from tropical !merican trees, called lignumvitae,which is a suitable material for water lubricated bearings, was used in the past.*ecause this wood is a natural material and its uality varies if lignumvitae of a

soft uality is used, wear is faster. Arom /6;: onwards, synthetic resins such asTeflon rubber and phenol resins were used e'perimentally. &henol resins werefound to make e'cellent water lubricated bushes there is no variation of uality asin lignumvitae and with a ma'imum allowable pressure of , twice that oflignumvitae and good wear characteristics, almost all bushes today are of phenolresin.


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&hoto./:+> 1ignumvitae

*ut in case of phenol resin, in some ships the wear to the bush is relatively fast.

This is because of the misalignment of rudder center line. !fter the rudder isremoved and the rudder center is re+ aligned , further abnormal wear to the bushwill be eliminated. %owever, it takes considerable time and money to align therudder center, therefore, some shipowners prefer to economi@e by renewing thebush at every docking survey rather than aligning the rudder center.

&henol resin or copper alloy is used in the bush of the neck bearing and copperalloy is used in the carrier bearing. The material used in the bush is always softerthan the material used in the sleeve, so the bush wears out faster than the sleeve.The advantage is that the bush can be easily replaced when it wears out.17.&." #lac( of slee*e

The cylindrical sleeve is e'panded by heating, and when the inner diameterbecomes large, the pintle is inserted by shrinkage+fitting. The twomembers are only held against each other physically therefore, the sleeve mightbecome slack due to vibrations or ingress of sea water between the members. Ifthe slack is e'cessive, the sleeve drops. ?hen the rudder is lifted, strike the sleevewith a test hammer and check for slack. If we press the sleeve lightly with a fingerwhile striking it with a test hammer, we might feel a slack of sleeve. If we find someslack, strike all around the sleeve with the hammer and record the slackedlocations. If the slack is found over >-< rd of all surface , the sleeve should bereplaced.


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Aig./:+:: Aalse clearance!ctual clearance 1eft side is much bigger than the value measured withfiller gauge.

Aig./:+:: ('amination of actual measurement


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Aig./:+:: ('aninination of sleeve sluck with test hammer,If the sleeve is sluck, the finger feels somthing like vacant.

Aig./:+:: Sketch showing sleeve sluckSlack is bigger in both & and S side

17-&-& Corrosion of b$sh retainer or s$pportThe bush retainer and support are a comparatively thiner welded rings made of

steel plate. If some part of this ring is corroded, bush might work loose and fall off.?hen they become e'cessively thin, the bush retainer or support should bereplaced, If the bush has been shrinkage+fitted into the shoe piece, it will not falloff however, there are instances of the bush disappered. The worn bush turnedinto a fine pieces, which in turn found its way between the pintle and the shoepiece then disappeared.


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Aig./:+


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Aig./:+ Corrosion of pintle /


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/ &intle corrosion> &intle corrosion and sleeve slack


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&hoto./:+< Corroded pintle

17-) 0ifting and 0owering $dderThe rudder weight is supported at the top or the bottom.It is suspended from a thrust bearing in the rudder carrier in the steering gearroom. %owever, in small ships, the rudder is supported with a heel disk below therudder. If the thrust disk or the heel disk wears out, the rudder itself comes down. Ifthe rudder comes down e'cessively, its connection with the steering gear becomesdefective therefore, the clearance between the shoe piece and the rudder shouldbe checked carefully during a bottom inspection. 3enerally, the designd clearancebetween rudder bottom andshue piece is >: mm to


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Aig./:+


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Aig./:+


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Aig./:+


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Aig./:+


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&hoto./:+9 Scratched thrust disk

&hoto./:+9: Combined thrust disk and bush

Thrust disk with integral bush is not recommended because when the disk isrenewed the sound bush also renewed.

17-)-3 $mping stopperIf the rudder is lifted when underway due to the wave impact or the contact withfloating ob)ects, and or bottom contact, the steering gear may be damaged. Toprevent such damage, a )umping stopper is provided.The )umping stopper, asshown in Aigure , may be fitted over the gudgeon or assembled in the ruddercarrier. the designed clearance is >.: mm ma'imum.There are no instances of damage or corrosion to the )umping stopperitself. %owever, if the clearance measured is found to be large, it can be

concluded that the rudder has moved down. *ecause a hanging rudderdoes not have a shoe piece, one does not know whether the rudder hasmoved down or not therefore, we recommend that you enter the rudder trunk andmeasure the clearance between the base of rudder carrier and the )umpingstopper.


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Aig./:+9/Humping stopper on the gudgeon


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Aig./:+9>Humping stopped under rudder carrier

Aig./:+9< easuring of the clearance between )unping stopper and the base ofrudder carrer in the rudder trunk


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17-6 $dder Corrosion17-6-1 Corrosion of r$dder plateIn old ships, the rudder plate corrodes and its thickness decreases, similar to wearto the shell plate. %owever, the rate of wear of the rudder plate is gradual and is

much smaller than that of the shell plate instances where the worn rudder platehas been cut out and replaced after measurement with a thickness gauge are veryrare. This is attributed to the large number of @inc anodes fitted for preventingcorrosion of the rudder plate.If the worn rudder plate is cut out for replacement, or a large thick double plate hasto be provided. 0nlike the hull structure, centring of the rudder is likely to beadversely affected because of welding the deformation.Therefore, the rudder plate should be removed, placed on a level block, andwelding work carried out while the centring of the rudder is checked.

Aig./:+99 Centering of rudder Aore + !ft and & +S side


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Aig./:+9 Aabrication of rudder

&hotp./:+= Centering of rudder on a level block

The rudder plate is placed on a level block and measured the center line. 1IS4!#($ocha, &2$T03!1

17.6.2 Corrosion d$e to erosionIrrespective of the age of ships, the upper, middle, and lower parts of the rudderplate and the gudgeon in fine high+speed ships sometimes suffer from e'cessivespongi form corrosion. This phenomenon is called erosion. The water flowgenerated by propeller rotation generates air bubbles in the flow at local locations


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where flow rate is high. ?hen these bubbles impinge on the rudder, they burst anddisappear, but cause microscopically large impacts on the rudder resulting in localcorrosion of the rudder plate.

Aig./:+9= (rosion of rudder

If the surface is eroded, and there is continuous flow of water over this surface,corrosion advances further. There are no fool+proof measures against corrosionthe rudder plate is sometimes built up by welding, and forged parts such as thegudgeon are sometimes covered with cement or Devcon, but at the ne'tdrydocking, similar corrosion can also be found in the cement therefore, effective

repair methods have not yet been discovered. %owever, as corrosion is localised,the strength of the rudder is not affected significantly, provided there is no hole inthe rudder through which water can enter therefore, this form of corrosion shouldnot be of much concern.

17-17 +wist in $dder #toc(!mong the damages of rudder the most troublesome damage is twisting of therudder stock. In furthermore, In most cases twisting is accompanied with by bendof the rudder stock.

!s mentioned in 6 of Section 8., ?hen we watch the rudder )ust aft in the drydock and the rudder is found to have swung to any & or S side, then the rudder

stock is likely to have twisted. *ecause when the ship is in dry dock always therudder is kept )ust midship.Twisting is caused due to the e'ternal force to the rudder plate in case ofgrounding, touching with mud, rock or floating ob)ects. ?ithout knowing that therudder is fi'ed, when the rudder is taken by force of steering gear the rudder stockwill be twisted. ?hile sailing , if the rudder suddenly responds strangely andbecomes heavier than usual, the rudder stock has probably twisted. %owever, ifthe angle of twist is small, there is practically no effect on steering


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?hen the twisting angle is less than two degrees, there is no problem.*ut when the ship heavily stranded, the twisting combined with bending of rudderstock.

17-17-1 Position of twist4ot the same as dents and cracks, It is very difficult to find the position of twist .The rudder stock above the neck bearing is slender, so the most cases it may beassumed that this part of the rudder stock will be twisted, *ut it is very difficult tocheck a position correctly.The twisting angle is measured after the rudder stock is oberhauled and placed onthe level block. The difference of the position of key way on the top of rudder stockand the position of rudder flange. In this case only we recogni@e the twisting anglebut we can not find the position of twisted area becaus there is no referencelongitudinal line on the rudder stock.

The rules of the 3ermanischer 1loyd the 3erman classification society prescribethe replacement of the rudder stock when the angle of twist is greater than /:degrees.

If the twist is /: degrees, the case where the twist has occurred throughout thelength of the rudder stock, say over a range of < m, is uite different from the casewhere the twist has occurred in a range of =: cm in the rudder stock while thetwist in the former is :.< degrees per unit length, the twist in the latter is nearly si'times this value. Aor instance, the report does not have an entry such as "twist wasfound over a distance of /,=:: mm from a point >,::: mm above the coupling inthe upward direction", because nobody knows the range of twisting. 2ne reasonfor this is that permissible values of twist have not been decided. In the newbuilding a reference line in the longitudinal direction should be marked on therudder stock.

17-17-2 Act$al eamples of twist!s mentioned above, 31 reuires replacement of rudder stock if the twist e'ceeds/: degrees, but we are inclined to think that this reuirement has been simplifiedbeyond our reasoning. $esults of damage and repairs of twisted rudded stocke'perienced during survey are as follows

17-17-3 epairing twistTwist occurs because of stranding and bottom contact, therefore, repair costs aregenerally covered by insurance. Aor this reason, there are many instances ofrenewing the rudder stock. %owever, as the rudder stock is a large forged block, aconsiderable time is reuired to procure materials. It is customary to carry outtemporary repairs and renew the rudder stock later.The following precautions should be taken during repairsB


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Aig./:+9; !d)ustment using a new bigger key

Aig./:+97 !d)ustment of uadrant


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> *igtwist angleIf the twisted angle is so large that repairs to the key alone are inadeuate, thekeyway can be built up by welding, the welded part checked for flaws by ultrasonictests, and a new keyway cut to suit the twisted angle. The rudder stock can beused even though it is twisted. %owever, because of the twist, the rudder stock

might have flaws that are not visible to the eyes therefore, it should be e'aminedby non+destructive tests such as ultrasonic flaw detection, magnetic particle test ordye penetrant test colour check.If very small cracks are detected, depending on the si@es of the cracks, they maybe chipped out or other measures adopted to eliminate them.This is a temporary repair method after repairs are carried out , the shipowner hasto procure a new rudder stock and replaced. however, these repairs may beaccepted as permanent repairs.

The wire rope test is described here for reference. In addition to the breaking testof the wire rope, after individual core wires of the rope is sub)ected to twisting testand coiling test. In the twisting test, one end of each core wire is fi'ed and theother end is rotated to twist the wire. If the core wire breaks before reaching aspecified number of turns, the rope is considered to be defective, irrespective of itstensile strength. Aor e'ample, in a =< mm diameter, 4o. < rope ; '/6 used formast stays, the diameter of one core wire is 9 mm. If the core wire is gripped at alength of 9:: mm and the twisting test performed, it should withstand at least /7turns before breaking. That is, the 9 mm diameter core wire should not breakbefore /7 rotations /7 '


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consideredB it should be ;: tuenes per minute.

8ig.17-4) Ad$stment of twistingThe old key way shown in full line is built up by welding a new key wayin dotted line is cut to suit the twist of the rudder stock M theta and thethe tiller position is ad)usted to suit the rudder.17-11 9thers17-11-1. 8lap r$dderIn order to improve the response of the rudder.The flap is fitted behind the rudderplate. This rdder is called *ecker rudder. Thepointofthe inspection is asfollowsB

The link mechanism and the connecting hinges including the flange are to becarefully inspected . If necessary, wear in the bearing may be measured at anoverhaul inspection. !t Special Survey, in addition to above inspection, operationtests are to be carried out .


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Aig./:+9= Alap rudder

17-11-2 ,ntermediate bearingThe rudder is generally supported at three points In case o f a hanging rudder, thesupporting poinnt is two. %owever, in rare cases, some ships have rudderssupported at four points, with an additional intermediate bearing below theuppermost support, namely the rudder carrier.

Aig./:+9; $udder with 9 bearings Aig./:+97 Intermediate*earing


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The bush in the intermediate bearing always shows abnormal wear and atthe every dodking, bush is renewed. This is because the centring of the rudder isincorrect. In this case it is better to abolishthis bearingto take off the bush andchange from four point supports to three points. !fter removal of the intermediatebearingthere is no problem in rudder operation.Three support points are

adeuate for a normal rudder.

17.11.3 $dder carrier!lthough no rerationship to bottom inspection, the rudder carrier is an importantpart connecting the rudder and the steering gear in the steering gear room. Aig. /:+8+> shows an e'ample of the construction of a rudder carrier the construction ofthe thrust disk carrier disk has already beendescribed .The points for inspecting the rudder carrier are listed below.

/ 1ooseness of bolts connecting rudder carrier to deck are to be e'amined withthe test hammer.> Cracks in deck connection part

Aig./:+97 Ai'ing the rudder carrier

In the construction shown in the figure on the left, crack will not apear in the deck.*utin the figure right, cracks might appear in the welded )ointat the inserted liner to the deck. when the thicker liner plate is welded to deck.Sometimescircumferenc cracks might be appeared in the weld )oining to thedeck.


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Aig./:+98 Ai'ing the rudder carrier fi'ed with edge

9 ?ear to thrust disk carrier disk cf. &hoto /:+9('amine wear and scratch to the thrust disk and the conditions of securing screws,as described in Section /:+8+> . ?hen the wear of the disk is minor but there islocal scratch on the carrier disk because of inadeuate lubrication, the disk may bereversed, oil grooves newly cut into the disk, and the disk reused, depending onthe saratch.

In ships euipped with electrohydraulic steering gear, always check the following

points when inspecting the rudder carrierB/ 1oose studs for gland of the hydraulic cylinder and oil leakage> !re there any flaw or scratch in the ramE


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should be carafully e'amined. Sometimes propeller shaft should bewithdrawn.The causes of this damage are contacting with a submerged or floating ob)ect orsmall material defect during manufacturing which developt to hair cracks, and ormetal fatigue.

11.1.2 !end of blade*end occurs because of impact of the propeller with other ob)ects they can bedetected easily even before the propeller is cleaned.11.1.3 Crac(sSmall cracks are overlooked in many cases. They cannot be detected unlessstagings are erected and after cleaning of each blade. (ven the hair cracks theyhave a possibility of e'panding and breaking the propeller blade. Thse hair cracksare discovered by dye penetration test.3enerally this test need not be carried out for the entire surface of the blade it iscustomary to check only the area from the root to :.9$ of the blade.In the previous dock if a stop+hole has been drilled at the crack end and the holehas been filled with a wooden plug, pay attention whether crack ia e'tended or not.In this case refer to previous Survey $ecord on this matter.

&hoto.//+/ *lade broken /


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&hoto.//+> *lade broken >


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&hoto.//+< *lade bent

11.1.4 CorrosionSimilar to the rudder, the propeller blade may be sub)ected to spongiform corrosionerosion due to cavitation. There is no good repair method the surface can besmoothed using a grinder, or depending on the position, the blade can be built upby welding, If the corrosion is severe, the corroded part may be cut out and usingthe approved material and repairedby welding. These welding repairs should beentrusted to the propeller manufacturers because weldingof copper alloys is verydifficult.


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&hoto.//+9 %air crack on the blade


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&hoto.//+= *lade errosion

11-2 ,nspection of !lades!ccording to data on cracks and broken blades, the blade is freuently cut at thelocation called the & point therefore, this part should be inspected with particularcare. The & point lies on the pressure side of the blade, and it is the point wherethe thickness of the blade is ma'imum and where the rounded radius of the bossterminates. The indication of the position on the propeller is similar to the conceptof the frame space indicating the position of the frame and beam shown in thefigure //+/ below.

The blade is divided into parts formed by measuring arcs from the centreof the propeller at every /:L of the radius of the propeller, such as :.9$, :.7$.The names of the blades are generally assigned as !, *, C, D and( or /, >,


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Aig.//+< The area for dye penetration test

Aig.//+9 &ropeller blade$ N $adius, Ct N Chode lenght in rudius r


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Table //+>+> Find of repair

11.4 8all of $ard ing! guard ring also called a rope guard is fitted between the propeller front face andthe stern frame to prevent floating ob)ects such as fishing nets from being fouledwith the propeller shaft. The guard ring is a split ring welded to the boss of thestern frame. It can come off easily if an ob)ect hits it. ! guard ring is not prescribedby the $ules, but if it has fallen off,it must be replaced by manufacturing a new ring and fitting it in place.

Aig.//+9 3urd ring

12.5 Clearance Meas$rementThe clearance between the propeller shaft and the bearing should be measured during thebottom inspection. There are two methods of


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measuring clearance, depending on the waterOsealing method for the shaft. Aor therudder, the clearances in the longitudinal fore+aft andtransverse p+s directions of the rudder shaft are measured, but for the propeller shaft,because the lower surface of the shaft is in contact with the bearing, only the clearance ofthe upper surface of the shaft has to be measured in case of a water++lubricated system.

Aig.//+= Clearanceof stern tube bearingAor an oil lubricationsystem, also measure the clearance at the lower surface.%owever, for an oilOlubricated system, clearances of the upper and lower surfaces haveto be measured, because the shaft sinkage is small. Clearances in the transverse directionneed not be measured because the shaft is rotating all the time.11.5.1 Clearances of sea waterBl$bricated bearingsSimilar to measuring the clearance of the rudder pintle, remove the guard ring, insert thefeeler gauge or the measuring wedge from the stern tube side and measure the clearance.*efore the lignumvitae dries out after the ship is drydocked, measure the clearance of theupper surface and record the results of the measure+ments in the Inspection $ecord Aorm+/. Aora ship with twin shafts, item /. in the form is for the propeller on starboard side, and item >.

is for the port side. If a twinOshaft ship has shaftbrackets, enter the measurements in the lower Dart of the form

Aig.//+; easurement of Clrarance


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Table //+> $esults of mesurement /The allowable ma'imum clearances according to shaft diameter are given below. If thevalues below are e'ceeded, the stern tube bearing material should be replaced orrepaired.

Table //+< !llowable ma'. clarance12.5.2 'eardown of oilBl$bricated bearings

0nlike lignumvitae used in waterOlubricated bearings, metal can be used in oilOlubricated bearings, and the clearance between shaft and bearing can be reduced. ?ear isalso small, and most modern ships use oilOlubricated bearings.Clearances should be measured at the same shaft positions as the previousmeasurement. To specify the shaft position, use the position ofthe propeller blade or the position of the main engine piston. 3enerally, this position isspecified according to the position of the propeller blade for e'ample, measure clearancewith blade ! at the top. If no hole for measuring sinkage is provided in the guard ring, theguard ring should beremoved, the screwed cap of the measuring hole removed, and a measuring instrumentsuch as #ernier calipers, soOcalled wear down gauge, inserted and distances from thebearing to the upper and lower surface of the shaft measured. The measued records is to

be entered in the survey report showing the position of measured point sucha sa the FeyTop or 4o. ; Crank Top. however, unless the bonnet is removed, the key position cannotbe )udged therefore, it is convenient to take a specific blade cylinder as the reference forsinkage measurement. In large ships today, propellers are generally keyless. Sinkage isthe difference in measurement at the time of inspection and measurement when the shipwas built. The standard limit for sinkage is :.< mm irrespective of the shaftdiameter. Sinkage should be determined by studying the properties of lubricating oil, andthe history of temperatures of the lubricating oil and bearing material. !n e'ample of theInspection $ecord is shown below.


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/ 2riginal

> 2verhaul of guard ring and cap bolt


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2/ ample of meas$rement res$lts for sin(age easurement results for two ships and their graphs are provided below forreference.The part above the kinked line shows the top, and the part below the kinked lineshows the bottom measurement values. The position of the blade does not

conform to the key top position but the 4o. 8 piston topposition.Ship / B Tanker, 7>, B Tanker, 9-/68/ 7>.7-7.;-7=-/68; 7>.6-7


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Aig.//+7 2il leakage from propeller boss

11.& !ow +hr$ster and #ide +hr$sterThese items are shipowners options, therefore, they need not be inspected underclass reuirements. %owever, if these items areinstalled on the ship, they should be inspected at the docking survey. Areuently

observed damage includes damage to guards at sea water ports due to impactwith submerged or floating ob)ects, and bent propeller blades. If the shaft seal isdefective, water entersin to the ship however, such incidents are not reported.Inspection results should be entered in the Survey $eport.?hen the stainless plate is used in the surface of the no@@le, the corrosion ofad)usent steel platesuould be carafully inspected.


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Aig.//+8 Damage of side thruster guard

Aig.//+6 Damage to side thruster


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12. Anchor12.1 eneral

!nchors, anchor chain cables, mooring ropes, and towing ropes are collectivelycalled "(uipment" . The number, weight and si@e of the euipment are determined

by the (uipment 4umber calculated according to the si@e of a ship.Conseuently, ?hen the dimensions of the hull are modified or the arrangement ismodified and the euipment 4umber e'ceeds the present number, the e'istingeuipment has to be changed tonew one.

Inspections of anchors and anchor chains are not the reuirements of the DockingSurvey but they are an inspection items in a Special Survey and IntermediateSurvey. *ut the inspection of the anchor and chain cable are carried out costomaryat the Doking Survey. !t the Docking Surveyanchors and anchor chain cabless are ranged on the dock floor and the surveyor

carry out the survey.%ereinafter e'plain the survey points and the e'amples of dmage and repairmethods.

&hoto./>+/ !nchor and chain cable ranged on the dry dock

12-2 ind and m$mber of anchor1ong time ago anchors are made of stone or wood. *ut in later days many kinds ofanchors are invented. %owever in these days anchors are made of steel and thefollowing types are widely used.


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1/ #toc( anchorI

&hoto./>+/ Stock anchor from "TheSea Aellow"

Aig./>+/ Stock anchor

2/ #toc(less anchor4ow almost all ships have a stockless anchor which euipped at bow on both &and S side.r.%arkins invented the stockless anchor in /8>< and r. atinse took a patent in/8=9. *ut the shipowners did not pay much interst in this new anchor.

!fter long testing, in /668 0F 4avy finally accepted ths anchor and graduallystockless anchor becomes popular. 2n the other hand, r.Scot invention the veryuseful %ause pipe. 4ow the stockless anchor and hause pipe are indespensableeuippment to all ships.


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&hoto./>+> Stockless anchorfrom ?ikipedia

Aig./>+/ Stockless anchor

Aig./>+< Terminology of stocklessanchor parts


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3/ @$mber of anchor!ccording to the old $ules , at least three anchors including the spare anchor areto be provided. %owever, from /68;, omission of the spare anchor has beenapproved at the reuest of the shipowners.

4/ #$r*e% items4ot only the inspection of !nchor and chain cable the Classification rules reueststhe following survey itemsB "!nchors are to be e'amined, and when the chaincables are ranged, they are to be e'amined. %awse pipes, chain lockers and cableholdfasts are to be e'amined. The Surveyor should ascertain that sufficientmooring ropes are provided on board. !s described above, note that in addition toinspection of anchors and anchor chains, inspection of chain lockers and chainstoppers is included in the Special Survey. Inspection of ropes generally includesconfirmation of the number, and it is customary to carry out a visual inspection ofropes."

12-3 efects and preca$tions d$ring inspection1/ !rea( and Crac(*reaks or cracks may develop in the shank or the arm because of defects in thecasting during manufacturing. 4aturally anchor should be renewed. It takes severalmonths to manufacture the new anchor.So the surveyormake the outstanding recommendations considering the delivery period for a newanchor. It is customary about si' monthsSmall cracks sometimes appears at the corners of the hole in the under surface ofthe crown. This part should be carefuly inspected after sludge is removed andcleaned. Depending on the degree of damage, repair can be carried out out byrewelding.

&hoto./>+< *roken shank / &hoto./>+9 *roken surface /


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&hoto./>+= *roken shank > &hoto./>+; *roken surface >

&hoto./>+7 *roken arm &hoto./>+8 *roken surface

&hoto./>+6 Crack at the end of arm


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&hoto./>+/: Crack at stopper

&hoto./>+// Crack at shank

2/ !end?hen the anchor is resting on the dock floor, sometimes both fluke ends do nottouch to the floor, it means, one fluke is raised higher than the other, then th

Docking Survey

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