Ship Construction for Mariners

7/26/2019 Ship Construction for Mariners

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Bottom Structure

KEEL

is located at the center line of the bottom structure and are the backbone of the ship.

Contributes substantially to the longitudinal strength and distributes local loading

caused by docking.

Commonest form is flat plate keel which is fitted in ocean-going vessels. Bar keel is used in small vessels (e.g. trawlers, tugs).

When double is fitted, flat plate type is always used.

Duck keel is provided in some double bottoms of some vessel. It carries the double-

bottom piping.

Single Bottom Structure

theverticalplateopenfloorsarefittedateveryframespaceandarestiffenedattheir

upperedge.

Acenterlinegirderisfittedandonesidegirderisfittedeachofthecenterlinewhenbeamislessthan10m.

Whenthebeamisbetween10and17m,twosidegirdersmaybefittedandadditional

continuousorintercostalstiffenersarefittediftheaspectratiow/lofbottomshellpanel

isgreaterthan4

Awoodceilingmaybefittedacrossthefloorsbutthisdoesnotconstituteaninner

bottomofferinganyprotectioniftheouterbottomisdamaged.


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Double Bottom

composedofouterandinnerwatertightbottomplatingtoprovidecompletewatertight

integrity

Thedoublebottomspaceisutilizedtocarryoilfuelandfreshwateraswellas

providingtherequiredballastcapacity.

Theminimumdepthofthedoublebottomdependsonthesizeofthevesselandis

determinedbytherulerequirementsofclassificationsocieties.

Theincreaseintheinnerbottomheightisalwaysmadebyagradualtaperinthe

longitudinaldirectiontoavoidsuddendiscontinuityinthestructure

Oneortwosidegirders,(continuousorintercostal),arefitteddependingonthewidth

Thesidegirders,andplatefloorshavelighteningholestoreducethestructuralweight,

andmanholestoprovideaccess.

Doublebottominthewayofmachineryspacesthatareadjacenttotheaftpeakare

requiredtobetransverselyframed.

Innerbottomplating

Innerbottomplatingmaybeslopedatthesidetoformabilgefordrainage

Themiddlestrakeoftheinnerbottomistheupperflangeofthecenter-linedocking

girderandthusheavierthanotherstrakes.

Ifgrabsareusedfordischargingcargoes,theplatethicknessisfurtherincreasedora

doubleceilingisused.

Floors

Floorsattheendsofthebottomtankspacesaremadewatertightoroiltightbyclosing

anyholesorweldingcollarsaroundanymembersthatpassthroughthefloors.

Solidsplatefloorsarefittedtostrengththebottomtransverselyandsupporttheinner

bottom

Theyruntransverselyfromthecontinuouscentergirdertothebilge.


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Thespacingofthesolidplatefloorvariesaccordingtotheloadssupportedandlocal

stresses.

Manholesareprovidedforaccessthroughtanksandlighteningholesarecutineach

solidplatefloor.

Transverselyframeddoublebottom

Transversesolidplatefloors,andbracketedfloorswithtransverseframes,provides

theprinciplesupportfortheinnerbottomandbottomshellplating.

Solidplatefloorsarefittedateveryframespaceintheengineroomandinthe

poundingregion

Oneintercostalsidegirderisprovidedportandstarboardwhere1014m

Thesidegirdersextendasfarforwardandaftaspossible.


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WritedownthenamesofShipStructuralcomponentsinshipbottom.ORbottomstructure

1.

Keel

1)

Flatplatekeel

2) Barkeel

3) Ductkeel

2. Singlebottomstructure

1. Openfloor

2. Garboardstrake

3. Transverseplatefloors

4. Intercostalsidegirderorside

keelsons

5.

Centergirder

3. Doublebottomstructure(transverselyorlongitudinally)

1. Centergirder

2. Intercostalsidegirder

3. Solidfloor

4. Tanktoporinnerbottom

5. Bottomlongitudinals

6. Bracketfloors

7. Flatplatekeel

8. Marginplate

4.

Bilgekeel

Fore end StructureMajorcomponentsare

1. Stem

2. Bulbousbow

3. Chainlocker

4. Hawsepipes

5. BowsteeringArrangement

6. Bowthruster


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2.Bulbousbows

3.Chainlocker

Chainlocker,whosedimensionsaredeterminedinrelationtothelengthandsizeof

cable,isarrangedfwdofcollisionbulkhead.

Afalsebottommaybeformedbyperforatedplatesonbearersarrangedataheight

abovethefloorofthelocker.

Itwillhelptocleanupthemud.

On many ships, soft nose stem, which is a solid

round bar is fitted from keel to the waterline region.

In the event of collision, it will buckle under load

keeping the impact damage to a minimum.

Vessel operating at higher speeds and those with

high CB are fitted with bulbous bow to reduce the

vessels resistance.

It involves a greater degree of plate curvature

Floors are fitted at every frame space and a centerbulkhead is fitted if the bulb is large.

Shell plating has an increased thickness to cover a

area likely to damage by the anchors and chains.


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4.Hawsepipe

5.Bowsteeringunits

Double-endedferriesareprovidedwitharudderateitherendthatislockedinposition

whenitisattheforeendofthevesselunderway.

6.Bowthrusters

Formaneuveringinconfinedwatersatlowspeedsand/orwhenveryaccurate

positioningisrequired,lateralbowthrustersareprovided.

Theyconsistofcontrollablepitchimpellerfittedinanathwartshipwatertighttunnel.

Toreducetheincreasedhullresistancebecauseofthetunnel,flush-mounted,butterfly

action,hydraulicallyoperateddoorsarefitted.

Deck, hatches and superstructures

Decks

Decksatdifferencelevelsinshipservevariousfunctions

Watertightdecksarefittedtomaintaintheintegrityofthemainwatertighthull

Freeboarddeckistheuppermostdeck

Strengthdeckformstheupperflangeofthemainhullgirder

Weatherdeckarecamberedtofacilitatethedrainageofthewater

Deckplating

Asthegreatestlongitudinalbendingstresseswilloccurovertheamidships,the

greatestdeckplatethicknessismaintainedover40%ofthelengthamidshipsandittapersto

aminimumthicknesspermittedattheendsoftheships.

Alllargeopeningsarewell-roundedtoavoidstress,withinsertedplatesfitted,unless

thecornersareparabolicorellipticalwiththemajoraxisforeandaft,localstress

concentrationsbeingreducedifthelatteristypeofcorneriscut.

Itprovidesaneasyleadforthecablefromthe

windlasstotheanchors.

Tubularhawsepipesarefabricatedandcastings

areweldedattheshellanddecktopreventchafin


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Deckmaybeframedtransverselyorlongitudinally

Withinthefwd7.5%oftheLOA,theforecastleandweatherdecktransversesare

closelyspacedandthelongitudinalscantlingsincreased.

Hatches

Hatch coaming

The construction and means of closing hatches in

watertight decks are contained within the ConditionsAssignment of Freeboard of the Load Line Conventio

Folding hatch cover

Single pull hatch cover

Direct pull hatch cover

Rolling hatch cover

Piggy-back hatch cover

Heights of coamings and cover closing arrangements depend on the hatch positi

Position 1: On the exposed freeboard deck, raised quarter deck or superstructur

decks within 25% of the ships length form fwd

Hatches at position 1have coaming at least 600mm high

Position 2: On exposed superstructure decks abaft the fwd 25% of LOA

Hatches at position 2 have at least 450 mm high coamings.

Coamings of 600mm or more are stiffened by a horizontal bulb flat at the upper

Coaming s of less than 600 mm are stiffened by a cope at the upper edge


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Bulwarks

Superstructure

Superstructuresmaybedefinedasthoseerectionsabovethefreeboarddeckthat

extendtotheshipssideoralmosttotheside.Deckhousesarethoseerectionsondeckthat

arewellwithinthelineoftheshipsside.

Thesestructuresarenon-continuous.Attheseiscontinuitieslargestressesmayarise

andadditionalstrengtheningwillberequired.

Longsuperstructuresexceeding15%oftheshipslengthandextendingwithin50%of

thevesselslengthamidshipsreceivespecialconsiderationastheycontributetothe

longitudinalstrengthoftheship

Aft-end StructureMajorcomponentsinaft-endare

1. Sternframe

2. Rudder

3. Steeringgear

4. Sterntube

5. ShaftbossingorAbracket

6. Propellers

Bulwarks fitted on weather decks are provided as protection for

personnel

They are of light scantlings.

Free ports are cut in bulwarks forming wells on decks to drain wate

It should be at least 1m high on the exposed freeboard and

superstructure decks


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1.Stern

2.Sternframe

o Theformofsternframeisinfluencedbythesternprofileandruddertype.

o Thesternframemaybecast,forgedorfabricatedfromsteelplateandsections.

o Topreventseriousvibrationattheafterendtheremustbeadequateclearancesbetweenthe

propellerandsternframe.

o Sternpostisofastreamlineform.

3.Rudders

o Ruddersonpresent-dayshipsaresemi-balanced.

o Balancedrudderswithlargeareafwdofaxis(25-30%)andunbalancedrudderswiththefull

areaaftoftheaxisarealsofitted.

o Theobjectofbalanceistoachieveareductionintorquebutthefullybalancedrudderwillat

lowanglestendtodrivethegear.

Construction:

o

Modernruddersareofstreamlinedform.

o Onesideplateispreparedandtheverticalandhorizontalwebsareweldedandtheotherpla

calledtheclosingplate,istheweldedtotheinternalframing.

o Adrainholewithaplugandaliftingholeisprovided

o Interiorsurfacesaresuitablycoated.

Basicallythreekindsofsterntypesexist

a.ellipticalorelevatedstern

b.cruiserstern

c.transomstern

Ellipticalsternisfoundinancientships

Cruisersternpresentsmorepleasantprofileandis

hydrodynamicallyefficientbutthetransomsternoffersagreaterdec

areaaft

Construction

Cruiserstern:itsubjectedtolargeslammingforces.Solidfloorsare

fittedineveryframeandaheavycenter-linegirderisfittedrightaft.

Sternplatingisstiffenedbycantframesorwebsand/orhorizontalstringers.

Cruiserstern:Cantframeisnotrequired.Deepfloorsandacenter-li

girderisfittedatthelowerregionofthestern


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4.Rudderpintles:Pintlesinthegudgeonshaveataperontheradiusanditsbearinglengthexceedsthediameter.

5.Rudderstocks

Itmaybeofcastorforgedsteelanditsmeterisdeterminedinaccordancewiththetorque

andanybearingmomentitistowithstand.

6.Rudderbearing:carriestherudderweight

7.Ruddertrunk:rudderstocksarecarriedinruddertrunkanditslowerendisnotwatertight

8.Steeringgear:Steeringgearareusuallyelectro-hydraulictype.

9.Sterntube

Twoformsexist:water-lubricatedbearingswiththeafterendopentotheseaandmetal

bearingsurfaceslubricatedbyoilwithbothendsclosed.

10.ShaftbossingandAbrackets Multi-screwvesselshavepropellersshaftsthatleavethelineofshellatsomedistancefw

ofthestern.

Theysupporttheshaftoverhang.

Abracketsfittedinlieuofbossingtoreducetheresistance.

11.Propellers

Theboreofthepropellerbossistaperedtofitthetailshaftandthepropellermaybekeye

ontothisshaft.

ThebladesofCPParemountedseparatedonthebossinwhichthepitchcanbechange

Shroudedpropellersareenclosedinafixednozzletoincreasethethrust.Thenozzlehas

reducingdiameteraft.

Electricpoddedpropellersarefittedinlargecontainerandpassengershipstoreducenoi

andvibrationandimprovemaneuverability.

Bulkheads

Verticalpartitioninashiparrangedtransverselyorforeandaftarereferredtoas

bulkheads.

Theyaresubjectedtohosetested

Functions

1. Thebulkheadsdividetheshipintoanumberofwatertightcompartmentsandsupportthe

externalandstructuraltransverseloading.


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2. Theyserveasahullstrengthmemberandsupportdeck,andbottomgirders,and

longitudinals

3. Theyresistanytendencyfortransversedeformationoftheship.

4. Themainhullbulkheadsarewatertighttocontainanyfloodingifacompartmentis

breached.

5. Bulkheadsareeffectiveforcontainingfires.

6. Thestrengthofthewatertightbulkheadismaintainedtothestrengthdeck.

Spacing(location) of watertight bulkheads

Theminimumnumberoftransversebulkheadsisthreewhentheshiphasanaft

engineroomandfourwhentheengineroomisnotattheaftend.

Forcollisionbulkhead,aheavybulkheadisspecifiedandlocatedsothatitisnotsofar

forwardastobedamagedonimpact.(minimumdistanceis10mfromforeend)

Theaftpeakbulkheadenclosesthesterntubesinawatertightcompartment,preventinganyemergencyleakage.

Itislocatedwellaftsothatthepeakwhenfloodedwouldnotcauseexcessivetrimbythe

stern.

Machinerybulkheadsprovideaself-containedcompartmentforboilerandengines,

preventingdamagetothesevitalcomponentsoftheshipfromflooding.

Eachofthemainbulkheadmayextendtotheuppermostcontinuousdeck.

ForBulkcarriers,reducedfreeboardnecessitatesfurtherconsiderationintothespacingothewatertightbulkheads.

Forapassengership,thespacingofthewatertightbulkheadsmustcomplywithSOALS.

Construction of bulkhead

Twotypesexist:plainandcorrugated

Plaintype:theplatingofaflattransversebulkheadisgenerallyweldedinhorizontalstrak

withthethicknessincreaseswithdepth.

Verticalstiffeningisprovidedintheformofweldedinvertedanglebarsoroffsetbulbplate

Verticalstiffenersmaybesupportedbyhorizontalstringerstoreducethescantling

Theboundariesaredoublecontinuouslyfilledweldeddirectlytotheshell,decks,andtank

top.


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Corrugatedtype

Theyaredesignedtoprovidesufficientrigiditytotheplatebulkheadinorderthat

conventionalstiffenersmaybedispensedwith

Thesebulkheadsarenormallyfittedwithtopandbottomspool.

Ifpossiblethepassageofpipingandventilationtrunksthroughwatertightbulkheadsis

avoided.

Ifpipespassthrough,pipesareflanged

Ifaventilationtrunkpassesthrough,awatertightshutterisprovided.

Water tight door

Toprovideaccessbetweencompartmentsoneithersideofawatertightbulkhead,

watertightdoorsarefitted.


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Theopeningisframedandreinforcediftheverticalstiffenersarecutinwayoftheopenin

Thewatertightdoorsareeitheroftheverticalorhorizontalslidingtype.

Theyaresubjectedhosetest.

Deep tanks

Theywerefittedadjacenttothemachineryspacesamidshipstoprovideballastcapacity,

improvingthedraftwithlittletrimwhentheshipwaslight.

Theywerealsousedforcarryinggeneralcargoesandalsoutilizedtocarryspecialistliqu

cargoes.

Mostshipsnowarefittedwithdeeptanksforwardtoimprovethetriminthelightcondition

Construction

Bulkheadsthatformtheboundariesofadeeptankdifferfromholdbulkheadsinthatthey

areregularlysubjectedtopressurefromaheadofliquid.

Thegreaterplatingthicknessofthetankboundarybulkheadsincreaseswithtankdepth,andwithincreasingstiffenerspacing.

Toprovidethegreaterrigiditytheverticalstiffenersareofheavierscantlingsandmore

closelyspaced.

Verticalstiffenersizesmaybereducedbyfittinghorizontalgirders

Cofferdamsarefittedbetweendeeptanksespeciallywhendifferentliquidcargosare

carried

Toreducethefreesurfaceeffect,acenter-linebulkhead,whichmaybeintactorperforatemaybefittedwherethetanksextendfromsidetosideoftheship

Bothswedgedandcorrugatedplatingmaybeusedintheconstructionofdeeptanks

Topside tanks Theyareusedforwaterballastorsometimesforthecarriageoflightgrains.

Theyarestiffenedinternallybylongitudinalframingsupportedbytransverses.

Shaft tunnel Theyareusedtoenclosedthepropellersshaftsinawatertighttunnelbetweentheaftend

ofthemachineryspaceandtheaftpeakbulkhead

Construction

Thethicknessofthetunnelplatingisdeterminedinthesamemannerasthatforthe

watertightbulkhead.

Thetopofthetunnelmaybeflatorwellrounded.

Stoolsarebuilttosupporttheshaftbearings


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Awalkwayisinstalledononesideoftheshafttopermitinspection

Oncompletiontheshafttunnelissubjectedtohosetest.

Pillars

Functions

Theprimaryfunctionistocarrytheloadofthedecksandweightsuponthedecksverticaldowntotheshipsbottomstructurewheretheseloadsaresupportedbytheupward

buoyantforces.Pillarsincargoholdsfulfillthefunctionandareincompressionwithout

bracketconnectionsattheirends.

Thesecondoneistotietogetherthestructureinaverticaldirection.Pillarsinthe

machineryspacesservethisfunctionandareheavilybracketedattheirendstopermit

tensileloadings.

Holdpillarsmaybeusedasmainstructuralelementstoreducethescantlingofthedeck

transversesanddeckgirdersbyreducingtheeffectivespansoftheseheavystructural

members.

Spacing of the pillars

Sincepillarsinholdswillinterferewiththestowagearrangements,widelyspacedpillarso

largesectionareused.

Commonarrangementistwo-rowsystem,withpillarsatthehatchcornersmid-lengthof

hatchsupportingdeckgirdersadjacenttothehatchsides.

Asthedeckgirdersizeistosomeextentdependentonthesupportedspan,whereonlya

mid-hatchlengthpillarisfittedthegirderscantlingswillgreaterthanthatwheretwohatch

cornerpillarsarefitted.

Pillarscanbeeliminatedifaclearspaceistobeprovided,butthedeckgirderwillbelargeandmaybesupportedbywebsatthebulkhead.

Construction

Holdpillarsareprimarilysubjectedtocompression

Idealsectionisthetubular.Hollowrectangularandoctagonalsectionsarealsoused.

Pillarshaveabearingfitanditisimportantthattheloadsattheheadandheelofthepilla

shouldbewelldistributed.


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Machineryspacepillarsarefabricatedfromangles,channels,orrolledsteeljoistsandare

heavilybracketed.

Ship Building Quality SteelThe following steels are predominantly used in shipbuilding

1.

Rolled plain steel (for plates and profiles, foundation, etc.)2. Rolled special steel (high-tensile steel, low-temperature steel for LNG tanker,

corrosion resistance for product tanker, non-magnetic steel for compass area)

3. Cast steel (rudder, stern, stem)

4. Forged steel (for anchors, chains, etc.)

IACSgradedthesteelsintofivedifferentqualities(GradeA,B,C,D,E)withGradeAbein

anordinarymildsteeltoLRrequirement.GradeBisbetterqualityandusedwhenthickerplates

arerequiredinthemorecriticalregions.GradeC,D,Epossessincreasingnotch-tough

characteristics,withGradeCbeingABSrequirements.

GradesA,B,D,DS,CS,andEaremostextensivelyused.

The Composition

Themicrostructureofshipbuildingsteelsconsistsofiron-carbide(cementite)dispersedin

matrixofferrite.

Steelforhullstructureismildsteel(0.15%-.23%C)withhighMncontent.

BothSandParekepttoaminimum(


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Steels Production WeldabilityRimmedSteels

Producedwithoutdeoxidizers PoorqualityNotusedashullsteelsinthicknessover13mm

Semi-killedSteels

Partiallyoxidized BetterqualityUsedashullsteels

KilledSteels Producedwithstrongdeoxidizingagents

Bestquality

Special Shipbuilding steels

1.High Tensile Steel

Theyareemployedinthemorehighlystressedregionsoflargertankers,containerships

andbulkcarriers.Theyallowreductionsinthicknessbutleadtolargerdeflections.

TheycontainAl,NbandVasadditives.

2. Corrosion-resistance Steel

Usedincargotankscontaininghighlycorrosivecargoes.

3.Abrasion-resistance Steel

Usedincargoholdsofbulkcarriers

4.Steels for lowtemperature

Usedwhereextraordinarycoolingeffectsexist(e.g.inrefrigerationshipsandLNGcarrier

Heat Treatment of Carbon Steel

1. Annealing

Steelisheatedslowlyto850-950.Candthencooledataveryslowrate.

Thiswillrelieveanyinternalstresses,softenthesteelandbringthesteeltoacondition

suitableforanotherheattreatment.

2.

Normalizing

Steelisheatedasincaseofannealingbutcooledinair.

Becauseoffastercooling,aharderstrongersteel(thanannealingproduces)withrefined

grainsizeisobtained.

3. Quenching (or Hardening)

Steelisheatedasincaseofannealingandnormalizingbutcooledinwateroroil.

Thisproducesaveryhardstructurewithahighertensilestrength.

4. Tempering

Quenchedsteelisfurtherheatedupto680 .Candcooledfairlyrapidly.Thiswillrelievethe

severeinternalstressesproducedbytheoriginalhardeningprocessandtomakethematerial

lessbrittlebutretainthehighertensilestress.


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5. Stress relieving

Torelieveinternalstress,steelisheatedthatnostructuralchangesareoccurredandslow

cooled.

Aluminum AlloyThe advantages of Al alloy over the steel are

1.

Low density

2. High strength-to-weight ratio

3. Corrosion resistance in certain environment

4. Retention of toughness at low temperature

5. Non-magnetic (useful for naval ships)

A major disadvantage is higher initial cost and fabrication costs.

The alloys have relatively low melting points and tend to lose strength rapidly upon

exposure to elevated temperature. (must use appropriate insulation)

Al alloys are frequently used in superstructure, and for entire hull structure of some ferrie

and small boats.Non-heat-treatable Al-Mg alloys of 5XXX series are widely used for marine

structures.

AL alloys are anodic to steel and could lead to aluminum sacrificing. It is difficult to join tw

metals avoiding corrosion. Either bolted connections with washers or an explosively bonded

steel/aluminum transition piece can be used.

Al Alloy TestsAl alloy plate and sections are subjected to tensile tests and bar Al are subjected- to a

tensile test and dump test.

Dump test requires compression of the bar until its diameter is increased to 1.6 times of t

original without cracks.

Classes, Rules and Regulations and IACSInternational Association of Classification Societies is held by twelve leading classification

societies.

1 DNV GL 5 ABS

2 BV 6 KR

3 LR 7 RINA

4 CCS 8 RS

9 NK 10 CRS

11 PRS 12 IRS


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IACS is the only non-governmental organization with the observer status at IMO able to

develop rules. {It endeavors to ensure that IMO technical or procedural requirements are easily

applicable and less ambiguous.}

The government body of IACS is the council, which considers and adopts unified

requirement (URs) and unified interpretations (UIs) of international codes and conventions.

Typical examples of UR are

Minimum longitudinal strength standard

Fire protection of machinery spaces

Use of steel grades for various hull members

Rules and regulations of the ClassesThe classification society(CS) is responsible to assure that the ships and marine structures

presented to it comply with Rules and Regulations that it has established for design, constructio

and periodic surveys.

Classification itself does not judge the economic viability of a vessel, neither is the society

a position to judge whether a vessel is ultimately employed according to the stated intended

service for which it was created.

Classification controls strength and quality of materials and workmanship in connection

with the ship, when built under Class.

The Certificate of Class is issued upon completion of construction

The CS each publish rules and regulations concerning

1. strength and structural integrity of the ship

2. provision of the adequate equipment

3. reliability of the machinery

Ships are built in accordance with Rules and Regulations of a CS in a procedure involving:

1. Technical plan review

2. Surveys during construction

3.

Acceptance by the Classification Committee4.

Subsequent periodic surveys for maintenance of class


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Periodic surveys

To maintain the assigned class, the vessel has to be examined by the society

surveyors at regular periods. At annual surveys, the general conditions of the vessel (e.g. t

freeboard mark, closing appliances, watertight doors, structural fire protections, etc.) are

assessed.

In-water survey may be acceptable in lieu of docking if high-resistance paint has beeapplied. Special surveys are due at five-yearly intervals with the amount of inspections

increasing as the vessel ages.

Testing of Material

Stress and strain curve of mild steel

CS Tests for hull materials1. TensileTest

Aspecimenissubjectedtoanaxialpullandaminimumyieldstress,ultimatetensilestress

andelongationareobtained.

Astandardgaugelengthequalto5.65timesthesquarerootofthecross-sectionalarea,whi

isequivalentofagaugelengthof5timesthediameterisadoptedbytheCS.

Strength=ability to resist deformation

Hardness=ability to resist abrasion

Toughness=ability to absorb energy

Ductility=ability to be deformed before it fails

Ship structures are designed to work within the

elastic range and much lower than the ultimate

tensile strength to allow for safety factor


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2. ImpactTest

Charpy-VorCharpy-Unotchtestisspecifiedataspecifictesttemperaturetodeterminethe

toughness:abilitytowithstandfractureundershockloading.

Thespecimenisplacedonananvilandthependulumisallowedtoswingsothatthestriker

hitsthespecimenoppositethenotchandfracturesit.Energyabsorbedinfracturingthespecime

isautomaticallyrecordedbythemachine.

3. Hardnesstest

Itiscarriedoutbyindentingthesurfacewithanindenterhavingaspecificgeometryundera

specifiedloadandresultingimpressionisexamined.Softermaterialwillindentmore.

4. Fatiguetest

S-Ncurveisobtainedbyrotating-bendingtest.Forsteelfatiguelimitsrangefrom35%to60%

ofthetensilestrength.

5.

AlAlloyTests

AlalloyplateandsectionsaresubjectedtotensiletestsandbarAlissubjectedtoatensilet

anddumptest.Dumptestrequirescompressionofthebaruntilitsdiameterisincreasedto1.6

timesoftheoriginalwithoutcracks.

Stress On a ShipThestressesashipexperiencedare

1. Stillwaterbendingstresses

2.

Wave-inducedbendingstresses

3. Rackingstresses

4. Torsionstresses

5. Pantingstresses

6. Poundingstresses

7. Bucklingstresses

8.

Otherlocalstresses

Localstresses

Transversestresses

Hoggingandsagging


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1.Stillwaterbendingstresses

Eventhoughtotalbuoyancyandweightareinbalanced,buttheyarenon-uniform,which

resultsinverticalshearforces.

Avesselwithexcessweightamidshipswillsag(deckincompressionandbottomshellin

tension). Avesselbendinginthereversemannerissaidtobehog.

Bendingstressis yI

M

Thegreaterthesecondmomentofarea[I],thelesserthebendingstresswillbe. varies

thedepthsquaredandsoasmallincreaseindepthofsectionwillreducethebendingstress.

Zy

whereZisthesectionmodulus.sectionmodulusisthequantitythroughwhichthedesignercan

controlthemaximumhullgirderstressandsafetyfactor.

Bendingstressaregreateroverthemiddleportionofthelengthandmaximumscantlingsmustbeprovidedover40%ofthelengthamidships

2.Wave-inducedBendingstress

3.RackingStress

4.Torsion

Asawavepassesbyavessel,theworsthoggingmoment

willoccurwhenthemidshipisonthecrestofawaveandt

bowandsternareinthetroughs.Theworstsaggingmome

willhappenwhenthebowandsternareontwocrests,with

themidshipinthetroughbetween.

Whetherforsaggingorhogging,theworstconditionwill

occurwhenthewavelengthisclosetothevessellength.

Whenashipisrolling,thedecktendstomovelaterallyrelativetothe

bottomstructureandtheshellononesidetomoveverticallyrelative

totheotherside.

Transversebulkheadsresistracking


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5.Pantingstress

6.Pounding

Pitchingoccursinthebottomoftheforeshipasaresultofheavingpitchingoftheship,

whichcanbereducedbyincreasingthebottom-platingthickness.Itismostsevereinalightly

ballastedcondition.

7.Bucklingstresses

Bucklingmayoccursinstructureundercompressionatastresslevelalotlowerthanthe

yieldstress.TheloadatwhichbucklingwilloccursisafunctionofthestructuresgeometryandthematerialsE.

8.otherlocalstresses

Atthediscontinuityofthehullgirderattheendofdeckhousestructures,athatchandoth

openingcornersandwhentherearesuddenbreaksinbulwarks,highlystressedoccurs .

WeldabilityOrdinarystrengthshipbuildingsteelsarereadilyweldable.

StainlesssteelsarereadilyweldablebyGMAW,GTAW,FCAWorSMAWusingfillerwireofcompatiblecomposition.

AlalloysusedinmarinecanbeweldedwithGMAWorGTAWorFSWbutGMAWisused

moreb/ohigherspeed.Whenjoiningthecommonmetalssuchasstainlesssteeltocarbonand

tocarbonsteel,galvaniccorrosionmustbeconsidered.

Alisnotweldabletosteelbyconventionalmethods.Anintermediatecompositeplate

material(lconsistingofAlandsteel),whichismanufacturedbyexplosionbondingtechniques.

Ashipheadingobliquely(45.)toawavewill

subjectedtorightingmomentsofopposite

directionatitsends,twistingthehullandputt

itintorsion.

Aheavytorsionboxgirderstructureincluding

upperdeckresistthetorsion

Itiscausedbythefluctuatingpressuresonthehull

attheendsandcausestheshellplatingtoworkin

andout.

Itisseverewhenthevesselisrunningintowaves

andpitchingheavily.


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Welding AdvantagesFortheshipbuilder

1. Weldinglendsitselftotheadoptionofprefabricationtechniques.

2. Easiertoobtainwatertightnessandoiltightness.

3. Jointsareproducedquickly

4.

Lessskilledlaborisrequired.

Fortheship-owners

1. Reducedhullsteelweight(MoreDeadweight)

2. Lessmaintenance

3. Smoothhullwhichresultsinreductionofskinfrictionresistance

Welding Processes used in Shipbuilding

Welding Processes generally used in Shipbuilding

1. Gas Welding

2. Shield metal arc welding(SMAW)

3. Gas Metal arc welding(GMAW)

4. Submerged arc welding(SAW)

5. Flux Core Arc welding(FCAW)

6. Stud welding(SW)

7. Tungsten inert gas welding(TIG) or(GTAW)

8. Metal inert gas welding(MIG)

9.

Plasma welding

10.Electro-slag welding(ES)

11.Electro-gas welding(EW)

12.Laser welding

13.Thermit welding

14.Fusion-stir welding(FSW)

1. Gas welding

Gas welding normally use oxyacetylene flame (3000.C).

It is slower than other fusion welding processes b/c process

temperature is lower than metal melting temperature.

The welding is obsolete nowadays in ship building.

2. SMAW

It is a process where heat is produced by an electric arc between a covered metal electrode and the work

Slag-shielded welding

Gas-shielded arc welding

ding


24/32

3. GMAW

It is an automatic or semi-auto process in which a welding arc is formed between the work and bare

electrode, which is continuously feed from the spool.

GMAW is the most important welding technology in shipbuilding.

4. SAW

Itis semi-auto or auto process where an arc is maintained between a continuous fed spool and a work ar

The welding zone is completely buried and shielded under a flux from a feed tube.

5.

SWAn arc is kept between stud and the work and heated for a time.

The stud is brought to the work by spring pressure.

It is used to attach studs, clips and hangers and insulation pins to structural members.

6. TIG or GTAW or TAGS

The arc is drawn between a water-cooled non-consumable tungsten electrode and the plate and shielded

by inert gas.

7. MIG or MAGS

Similar to TIG, but electrode is consumable metal wire.

8. Plasma Welding

Similar to TIG, but the tungsten electrode is within the body of the torch and the plasma arc is forcedthrough a fine-bore copper nozzle. Three modes can be achieved

Micro plasma

Medium current

Keyhole plasma

9. ES and EW

Are high-deposition rate process

Cause a greater degree of grain growth in HAZ and require local normalizing treatment afterwards.

ES

Used for heavy casting structure components such as stern frame.

Current passes into the weld pool through the wire.

Welding is achieved by resistance path heating through the flux.

EW

It is arc welding with features of gas-shield welding and ES.

Used for welding thick plates with square or vee edge preparations.

10.Laser Welding

1. Two type of laser sources: 1.CO2 and 2. Nd: YAG crystals

The laser beam focuses via mirrors on the surface of the work piece. After reaching the vaporization

temperature, a steam capillary is formed in the work. This allows deep, narrow welds with practically

parallel sides with small thermic loads and small brittle Heat Affected Zone.Used for sandwich panel structures.

11.Thermit welding

Used to join large steel sections such stern frame.

It is a fusion process heated by a mixture of powdered Al and iron oxide.

12.Friction stir welding

It is a solid state process that relies on the friction between two parts to generate heat to soften the met

and provide a joint.

Currently used only for welding Al alloy plates for high-speed crafts and honeycomb panels.


25/32

Welding practice

Edge preparation (2015)

Forplatethicknesslargerthan5-6mm,multi-passweldsareneededtoachieveafull

penetrationweld.

Unlessapermanentbackingbaroronesidedweldingisused,abackrunisrequiredaftechoppingorgouging.

Tackweldsarelightrunofweldmetalusedtoholdpatesandsectioninplacepriorto

completionofthefilletoffullbuttweld.

Theseareshortlightrunsofweldmetalwhichmaybeweldedoverorcutoutduringthe

finalweldingofthejoint.

Filletweldsmaybecontinuousorintermittentinachainorstaggeredfashion.


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Weldingthickerplatesnecessitatebevelingtheedges,whichisdonebygasorplasmacuttingormechanicalmethods.

Platesofvaryingthicknessmaybebuttweldedasshowninthefollowingfigure.

Welding Distortion (14,12)

Distortionsarisesformexpansionofthemetalwhenheatedandcontractsuponcooling.

Thecausesofdistortionarecomplexandinvolveanyresidualstressesinthesteelplate.

Tocontainthein-planedistortionsuchasshrinkage,theplatesarecutover-sizedsothat

theeffectofshrinkageistobringthemtothecorrectshape.

Highdepositionelectrodes,automaticwelding,andhighweldingcurrentsreducedistortio

Theleastamountofweldmetal,depositedwithfewpasses,isdesirable.

OnDouble-Vjoints,weldalternatelyonbothsidesoftheplate.

Jointsthatmayhavethegreatestcontractiononcoolingshouldbeweldedfirst.

DistortionControl

1. Avoid over-welding

2. Edge preparation & fit up

3. Intermittent welding

4. Minimum no: of pass

5. Welding near neutral axis

6.

Balancing weld around neutral axis

7. Backstep Welding

8. Pre-bending

9. Back to back welding

10.Weld sequence (Joint)

11.Sequence weld (Scatter fillet welds)


27/32

Welding FaultsVariousfaultsmaybeobservedinbuttandfilletwelds.Thesemaybeduetoanumberof

factors:baddesign,incorrectweldingprocedure,useofwrongmaterials,andbadworkmanship


28/32

Welding Sequences

Non-destructive testing1. Dye penetrant

2.

Magnetic particle3. Visual examination

4.

Radiographic

5. Ultrasonic

6. Gauging

7. Sound or percussion test

8.

Pressure testing9. Penetrate fluorescent test

10.Sonic test

11.Eddy current test12.Thermography

Dyepenetrant

Itwillshowasurfaceflawafterthecastinghasbeenwashedafterapplyingthedye.

Itisoftenluminousandisrevealedunderanultraviolentlight.

Rarely used nowadays

AtTintersectionsitisnecessarytoweldthe

buttfirstfully,thengougeouttheendstorenewtheseamedgepreparationbeforeweldingthe

seam.

Generalpracticewhenweldingshellpanels

istostartbyweldingthecentralbuttsandthen

adjacentseams,workingoutwardsboth

transverselyandlongitudinally.

Thelowersideplatingseamsshouldnotbe

weldedbeforetheupperseams.


29/32

Magnetic particle

It is carried out by magnetizing the casting and spreading a fluid of magnetic particles on t

surface. Any discontinuity such as a surface crack will show as the particles concentrate where

there is an alteration in the magnetic field.

Visualexamination

Exceptsubsurfaceandinternaldefects,incorrectbeadshape,highspatter,undercutting,badstopandstartpoints,incorrectalignment,andsurfacecracksareallfaultsthatmaybe

observedbyvisualinspections.

Itisaroutineprocedureanditscostislow.

Radiographic

Itisdonebyrecordingchangesinradiationdensityemittedfromonesideofasubjectwh

itsanothersideisexposedtoradiation.

Itisusedtorecordtheconsistencyoftheweldmetal.(avoidwillshowupdarkershadow

ontheradiograph.)Itposespotentialhazardstotheoperatorandinspector.

Ultrasonic

Ultrasonicenergyissaferandusefulforlocatingfinecracksmissedbyradiography.

Anultrasonicimpulsefromacrystalpassesthroughthematerialandreflectedbacktothe

crystal.

Anydiscontinuitywilldeterminetheproportionofimpulsereflectedbacktothecrystal.

Thepatternofreflectionisrevealedonacathoderaytubeandanexperiencedoperator

recognizesflawfromthedisplay.

Classification society weld tests: destructive test CSspecifydestructivetestsareintendedtobeusedforinitialelectrodeandweldmateria

approval.Testsaremadeforconventionalelectrodes,deeppenetrationelectrodes,wire-gasan

wire-fluxcombinations,consumablesforelectro-slagandelectro-gaswelding,andconsumable

forone-sidedweldingwithtemporarybacking.Tensile,bendandimpacttestsarecarriedouton

thedepositedweldmetalandweldedplatespecimens.

Shell plating system Thebottomandsideshellplatingconsistsofaseriesofflatandcurvesteelplatesgenera

ofgreaterlengththanbreadthbuttweldedtogether.

Bottomshellplating

Throughoutthelengthoftheshipthewidthandthicknessofthekeelplateremainconsta

whereaflatplatekeelisfitted. Itsthicknessisneverlessthanthatoftheadjoiningbottomplatin

Strakesofbottomplatingtothebilgeshavetheirgreatestthicknessoverthe40%ofthe

LOAamidships.Thebottomplatingthentaperstoalesserthicknessattheendsoftheship.


30/32

Sideshellplating

Thegreaterthicknessofthesideshellplatingismaintainedwithin40%ofthevessels

midshiplengthandthentaperstotherulethicknessattheends. Thethicknessmaybeincreasedinregionswherehighverticalshearstressesoccur.

Theupperstrakeoftheplatingadjacenttothestrengthdeckiscalledshearstrake.

Itisdressedsmoothandtheweldingofbulwarkstotheedgeofthesheerstrakeisnot

permittedwithintheamidships.

Allopeningsinthesideshellhaveroundedcorners,andopeningsforseainletetc.areke

clearoutofthebilge.Whenthisisnotpossible,theopeningsaremadeelliptical.

Transversframingsystem Itwillconsistofmainandholdframeswithbracketstopandbottom,andlightertweende

withbracketsatthetopsonly.Scantlingsofthemaintransverseframesareprimarilydependen

ontheirposition,spacinganddepth,andontherigidityoftheendconnections.

Webframes,i.e.built-upframesconsistingofplatewebandfaceflat,wherethewebis

considerablydeeperthantheconventionaltransverseframe,areoftenintroducedalongtheside

shell.

Webframesisintendedtoincreasetherigidityofthetransverseshipsection.

Webframeisrequirednotmorethanfivefamespacesapartat

1. Machineryspaces

2. FwdofthecollisionBHD

3. Inanydeeptank

4. Intweendecksabovedeeptanks

Webframeisrequiredateveryfourthframeapartinthetweendeckabovetheaftpeaktank.


31/32

Longitudinalframingsystem

Ifthesideshellislongitudinallyframedoffsetbulbsectionswilloftenbeemployedwithth

greatersectionscantlingsatthelowersideshell.Directcontinuityofstrengthistobemaintaine

Transversewebswhicharespacednotmorethan3.8mapart,inshipsof100mlengthorless

arefittedtosupportthesidelongitudinals.Largershipsrequiredtohaveadoublehullare

longitudinallyframedatthesideswithtransversewebsarrangedinlinewiththefloorsinthe

doublebottomtoensurecontinuityoftransversestrength.

Bilge keel

Itsfunctionsare

1. tohelpdumptherollingmotionofthevess

2. toprotectthebilgeongrounding.

3. Toincreaselongitudinalstrengthatthebilg

Thegroundbarthicknessisatleastthatofthe

bilgeplateor14mm,andthematerialgradeisthsameasthatofthebilgeplate.

Connectionofthegroundbartotheshellisb

continuousfilletweldsandthebilgekeelis

connectedtothegroundbarbylightcontinuouso

staggeredintermittentweld.

Bilgekeelsaregraduallytaperedandfinishin

wayofaninternalstiffeningmember.


32/32

1isfortheflatorhorizontal(piperolled)position. Fisforfillet2isforthehorizontalorvertical(pipe)position. Gisforgrooveweld

3isforverticalposition 4isforoverheadposition

5isforapipeinfixedhorizontalposition 6isforapipein45 Risforrestrictedposition

Throat thickness is leg length * cos(45) or .7 leg length

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