SSC-220

A LIMITED SURVEY OFSHIP STRUCTURAL DAMAGE

This document has been approved

for public release and sale; its

distribution is unlimited.

SHIP STRUCTURE COMMITTEE

1971

MEMBER AGENCIES:

UNl IEO STATES COAST GUARD

YAVAI stIIt>sYslm4s CO MMANO

M(1 llARY SF.Ai (FT (:COMMAND

MARITIME ADMINISIRA IION

AM! RI(:AN B(IRt AU of SHIPPi NC

SHIP S’VRUCTURE COMMITTEEAN INTERAGENCY ADVISORY

C04MITTEE DEOICATEO TO IMPROVING

THE STRUCTURE OF SHIPS

AODRESS CORRESPONDENCE TO:

SECRETARY

SbllP STRtll:l(lHE COMMITTEE

u.S. CO*3T Gk’A1V2 IHEAOOUARIE IIS

WASHIN(+IIIN, !I.C. MM 205(10

S1{ 1891.971.

In the continuing <:ffort to maintain a high degree of

structural reliabi:.ity in new ship designs , the Ship

Structure Commit tef, has undertaken a project to identify

areas of structural:,.weakness through the systematic

survey of vessel d:lmage reports. From this i.dentificat.ion

structural improvement can easily follow.

This report contail,s a description and results of the

first step i.n this systematic survey.

A-2%’fz”W. F. REA. 111

Rear Admiral. K!.S. coast Guard

Chai rrnan, Ship Structure Committee

SSC-220

Final Report

on

Project SR-189, “Ship Structure Reliability Analysis”

to the

Ship Structure Committee

A LIMITED SURVEY OF

SHIP STRUCTURAL OAMAGE

Seth Hawkins,

by

George H. Levine, and Robert TaggartRobert Taggart, Inc.

under

Department of the NavyNaval Ship Engineering CenterContract No. NOO024-70-C-5214

This document has been approved for public re lease and

sale; its distribution is unlimited.

U. S. Coast Guard HeadquartersWashington, D. C.

1971

ABSTRACT

A limited investigation, conducted to determine theavail abil ity of data on ship casualties involving structuraldamage, revealed 824 applicable cases. A method was devisedfor reducing reported casualty data into a format adaptableto automatic tabulation and analysis. Collision with fixedand mobi 1e structures was found to be the predominant causeof structural damage; heavy weather damage to the forefootand forward weather deck al so occurred with significant fre-quency. Patterns of damage frequency and location exi st.edon a number of cl asses of shi ps. These have been interpretedto indicate how structures could be altered to reduce thedamage sustained. Recommendations are made to continue thedata CO1 lection and analysis program and to investigate moreextensively the ways in which significant structural designinformation can be extracted.

ii

CONTENTS

PaJg

INTRODUCTION . . . . . . . . . . . . . . . . . . . . ...1

SOURCES OF CASUALTY DATA..... . . . . . . . . . . . . 1

CASUALTY DATA COLLECTION. . . . . . . . . . . . . . 3

SCOPE OF STRUCTUR,!L CASUALTY DATA . . . . . . . . . 3

STRUCTURAL CASUALTY PROBLEM AREAS . . . . . . . . . 8

Collision Damage . . . . . . . . . . . . . . . . ...8

Heavy Weather Slamming Damage . . . . . . . . . . . . 13

Heavy Weather Damage, Forecastle and Weather Deck . . 18

INTERPRETATION OF STRUCTURAL CASUALTY DATA. . . . . . . 21

CONCLUSIONS AND RECOMMENDATIONS . . . . . . . . . . 24

iii

LIST OF ILLUSTRATIONS

m

1

2

3

4

5

6

7

8

9

10

11

~

SAMPLE DATA FORM . . . . . . . . . . . . . . . . ...4

LONGITUDINAL AND VERTICAL LOCATIONOF DAMAGE, ALL CAUSES -- ALL SHIPS . . . . . . . . . 7

LONGITUDINAL DISTRIBUTION OF COLLISION DAMAGE. . . . . 9

VERTICAL DISTRIBUTION OF COLLISION DAMAGE. . . . . . 9

DAMAGE LOCATION PROBABILITY CONTOURS FROMCOLLISIONS WITH PIERS, QUAYS, AND LOCKS. . . . . . . .11

DAMAGE LOCATION PROBABILITY CONTOURS FROMCOLLISIONS WITH VESSELS ALONGSIDE. . . . . . . . . . .11

EXTENT AND LOCATION OF SLAMMING DAMAGEFOR VARIOUS CARGO SHIP DESIGNS . . . . . . . . . . . .14

CUMULATIVE EXTENT AND LOCATION OF SLAMMING DAMAGE. . .15

STRUCTURAL DETAILS IN AREA OF BOTTOM DAMAGE. . . . . .16

ARRANGEMENT OF FORECASTLE AND BULWARK. . . . . . . . .ZO

SKETCH OF BULWARK, DESIGN ‘A’. . . . . . . . . . . .21

iv

LIST OF TABLES

Table—

1

2

3

4

5

6

7

8

9

10

11

12

13

STRUCTURAL CASUALTY DATA BASE . . . . . . .

GENERAL DISTRIBUTION OF STRUCTURAL DAMAGE . . .

DISTRIBUTION OF FAILURES BY STRUCTURAL ELEMENTS

DISTRIBUTION OF TYPE OF FAILURE . . . . . . . .

CLASSES OF SHIPS SELECTED FOR

F%NJg

. . 5

. . 7

. . 7

. 7

OETAILED OAMAGE ANALYSIS. . . . . . . . . . . . . . . 8

VERTICAL DISTRIBUTION OF OAMAGEDUE TO STRIKING PIERS . . . . . . . . . . . . . . ..1O

VERTICAL DISTRIBUTION OF OAMAGEFROM VESSELS ALONGSIDE. . . . . . . . . . . . . . .10

VERTICAL OISTRIBUTION OF DAMAGEDUE TO STRIKING LOCKS . . . . . . . . . . . . . ...10

FAILURES RESULTING FROM STRIKING PIERS. . . . . . . .12

FAILURES RESULTING FROM STRIKING VESSELS ALONGSIDE . .12

FAILURES RESULTING FROM STRIKING LOCKS. . . . . .12

SUMMARY OF BOTTOM SLAMMING DAMAGE . . . . . . . . . .13

SUMMARY OF WEATHER DECK DAMAGES IN HEAVY WEATHER. . .19

v

SHIP STRUCTURE COMMITTEE

The SHIP STRUCTURE COMMITTEE is constituted to prosecute a researchprogram to improve the hul1 structures of ships by an extension of knowledgepertaining to design, materials and methods of fabricati on.

RADII W. F. Rea, III, USCG, ChairmanChief, Office of Merchant Marine Safety

U. S. Coast Guard Headquarters

Capt. J. E. Rasmussen, USN Mr. E. S. DillonNaval Ship Engineering Center ChiefPrince Georges Center Office of Ship Construction

Maritime AdministrationCapt. L. L. Jackson, USNMaintenance and Repair Officer Mr. K. Morland, Vice PresidentMilitary Seal ift Command American Bureau of Shipping

SHIP STRUCTURE SUBCOMMITTEE

The SHIP STRUCTURE SUBCOMMITTEE acts for the Ship Structure Committeeon technical matters by providing technical coordination for the determinationof goals and objectives of the program, and by evaluating and interpreting theresults in terms of ship structural design, construction and operation.

NAVAL SHIP ENGINEERING CENTER U . S. COAST GUARD

Mr. P. M. Palermo - Chairman LCDR C. S. Loosmore, USCG - SecretaryMr. J. B. O’Brien - Contract Administrator CDR C. R. Thompson, USCG - MemberMr. G. Sorkin - Member CDR J. W. Kime, USCG - AlternateMr. H. S. Sayre - Alternate CDR J. L. Coburn, USCG - AlternateMr. 1. Fioriti - Alternate

NATIONAL ACADEMY OF SCIENCESMARITIME ADMINISTRATION

Mr. R. W. Rumke, LiaisonMr. F. Oashnaw - Member Prof. R. A. Yagle, LiaisonMr. A. Maillar - MemberMr. R. Falls - Alternate SOCIETY OF NAVAL ARCHITECTS & MARINEMr. R. F. Coombs - Alternate ENGINEERS

AMERICAN BUREAU OF SHIPPING Mr. T. M. Buermann, Liaison

Mr. S. G. Stiansen - MemberMr. F. J. Crum - Member

OFFICE OF NAVAL RESEARCH

Mr. J. M. Crowley - MemberBRITISH NAVY STAFF

Dr. W. G. Rauch - Alternate Dr. V. Flint, Liaison

NAVAL SHIP RESEARCH & DEVELOPMENT CENTERCDR P. H. H. Ablett, RCNC, Liaison

Mr. A. B. S*avovy - Alternate WELOING RESEARCH COUNCIL

MILITARY SEALIFT COMMAND

Mr. R. R. Askren - Member Mr. K. H. Koopman, LiaisonLt. j.g. E. T. Powers, USNR - Member vi Mr. C. Larson, Liaison

INTRODUCTIONThegoalofProjectSR-189,“ShipStructureReliability

Analysis”,istoconducta surveyofshipstructuralfailuresasrelatedtotypes,frequency,andlocationinordertodevelopmeaningfultrendsandtoassessthepossibilityofeliminatingorminimizingthesefailuresandsoimprovestructuralreliability.Thisreport,coveringoneyear’seffort?presentsthedatacollectedduringthesurvey,togetherw~thconclusionsandrecommendations.

Briefly,theplanwasto:

0 Surveydatasourcestodeterminetheamountandkindsofdataavailable.

● Developa datacollectionformatcompatiblewiththeinformationavailableateachsource.

.Collectavailabledatafromeachsource.● Analyzethedatacollected.● Reporttheresults.

TheshipsrepresentedinthedatabaseareU.S.built,subsidizeddrycargoships,anda fewMSCtankers.ModernshipdesignsdifferfromtheirWorldWarIIpredecessorsinmanyrespectsandmodernshipsteelsgainedbroadacceptanceinthemid-1950’s;accordingly,onlyseagoingshipsbuiltafter1955areincludedinthisstudy.SOURCESOFCASUALTYDATA

ShipstructrualcasualtydatawereobtainedfromthefilesoftheU.S.CoastGuard(USCG),theMaritimeAdministration(MARAD),andtheMilitarySealiftCommand(MSC).Thisinformationcomprisesthedatabasefromwhichanalysesweremadeofstructuraldamage.AmericanBureauofShipping(ABS),U.S.SalvageAssocia-tion,andSalvageAssociationofLondonreportswereoftenapartofthefilesoftheaforementionedagencies,andprovidedamajorportionofthedetailedinformation.

A few~ommentsareinorderregardingthekindsofinforma-tionderivedfromeachsource:

AmarinecasualtymustbereportedtotheCoastGuardwhen-everitresultsindsmagetopropertyinexcessof$1,500.00,materialdamageaffectingtheseaworthinessorefficiencyofthevessel,strandingorgrounding,lossoflifeorinjurywithincapacitationfinexcessof72hours(46Cn97.01-1).Inaddition,aReportofStructuralDamage,CollisionDamageorFireDamage(FormCG2752)issubmittedincasesof:

..—

2

1. ClassI StructuralFailure:a failurewhichhasweakenedthemainhullgirdersothatthevesselislostorisina dangerouscondition.

2* ClassIIStructuralFailure:a failurewhichdoesnotendangerthevesselbutinvolvesthemainhullstructureata locationwhichexperiencehasindicatedisapotentialsourceofdangerousfailure.

CollisionorGroundingwithdamageinexcessof$1,500:60.

4* FireorExplosionwithdamageinexcessof$1,500.00.CasualtieswhichhavebeenreportedtotheCoastGuard,butforwhicha Form2752hasnotbeencompleted,werenotincludedinthisstudy.

MARADfilescontaindataonU.S.shipsparticipatinginthesubsidyprogram.Recordsforsubsidizedvoyagesduringtheperiod1966throughmostof1969wereavailable.Mostoftheearlierrecordshavebeendestroyedbutsomedatawereobtained,onspecificstructuralcasualtiesoccurringduringtheperiod1961through1965,fromothersourcesatMARAD.Itisworthyofmetitionthatsomeshipsgoinandoutofsubsidy,thusinformationonstructuralcasualtiesoccurringduringout-of-subsidyoperationmaynotbeincludedinthefiles.ThemajorityoftherelevantdatacontainedinMARADfilesare intheformofinvestigativereportsfromoneormoreofthefollowingorganizations:U.S.SalvageAssociation,ABS,andSalvageAssociationofLondon.

FilesoftheMSCcontaininformationonshipsoftheirfleetfromdateofconstruction.ThemostusefulsourcesofdatafoundinthesefileswereABSsurveyreports.

Insummary,directaccesstostructuralcasualtyfileswaspossibleattheU.S.CoastGuard,MARADandMSC.Informationatthesesourceswhichbecameapartofthedatabaseforthisprojectcomprised:

1. CasesforwhichaUSCGReportofStructuralDamage(FormCG2752)wasfiled.

2. CasesforU.S.flagshipvoyagessubsidizedbyMARADduringtheyears1961through1969.TherelevantinformationintheMARADcasefilesis,forthemostpart,intheformofreportsfromU.S.Salvage,ABS,orSalvageAssociationofLondon.

3. CasesforMSCships,fromtheirdateofconstruction,whereABSsurveyswereconducted.

3

CASUALTYDATACOLLECTIONAttheoutsetoftheprojectatentativelistingofinfor-

mation~equirementswasderived.Aftervisitingthevariouspotentialdatasourcesandperusingrepresentativecasefiles,arevisedformatwasdevelopedforuseintheactualdatacollec-tioneffort.A copyofthisformisshowninFigure1.

Inadditiontoa casenumber,thedesiredinformationisdividedintotenbasiccategories:

1.2.3.4.5.6.7*8.9*10.

ShipDataInformationSourceCircumstancesCauseDispositionExtentTypeofFailureTypeofStructureLocationRemarks

Eachbasiccategoryisthendividedintosubcategorieswithcodeddesignationsforeachitemandsub-itemsoastopermittheuseofautomaticdataprocessingequipment.Theentiredataformatasshowncanhereducedtoa singlecardforbasicshipdataandanothercardforthedetailsofthespecificstructuralfailure.Thusfora givenshipforwhichtherearetenindividualstruc-turalcasualtycases,therewouldbeelevendatacards.

Costofrepairisnotincludedonthedataform.Formostofthecasesinvestigatedinthisstudy,costinformationwasnotavailable.

SCOPEOFSTRUCTURALCASUALTYDATAThesurveyofstructuralcasualtyrecordsresultedina data

baseof824casesfrom146shipsoverthe15yearsconsidered.ItisdifficulttodeterminethetotalnumberofU.S.Flagshipsoperatedduringthatperiod.However,forcomparisonpurposes,inmid-1969therewere244subsidizedmerchantshipsofover1000grosstonsinanoperatingstatusintheU.S.FlagFleet.InadditionMSCwasoperating23shipsbuiltafter1955.

Table1representsabreakdownofthedatabasebyallegedcauseofthecasualty.

SHIPSTRUCTURERELIABILITY ANALYSIS l.ca== No.2.N.me 3.Off,No.

SHIPDATA ABSRec. 4. TypeofVe$mlO?her

5-Length 6- Brnadth 7’ Depth 8. Draft 9. Displacement tc.n5

10-YeCIrBuilt ““Gross Ton. 12.H.11Material:lh.oln 13-N0. of Holds

i4.‘=”=:=:%’ ---??aY..BY

Yaorof Last MalorConversion

17. 18. 20.MachineryLocation: lDMidshi Ps SuperstructureLength Bulb

2~ Aft 19. 21.SuperstructurePosition ‘b

24. a) FilesINFORMATIONSOURCE

24. b) Surveyreport“1 HUSCG2 ❑MARAD

1 ❑ AB52 ❑ USSALVAGE

22.S.rvey Date 3 flMSTS 3 ❑ SALVAGEASSOCIATIONLONDON23.S.rv.y Lo..ti.n 4 D ABS

5 ❑uSSALVAGEOther

25.G=og.L..atI.. 26.Ra.t. FromCIRCUMSTANCES OR 27.To

28.1funknown,fail. refound.. annualsurveyl~ or drydockingzn

29. ShipSpeed I30”Course 31.LoudConditions:1 ❑BollcIst L32-Date97 nA. chored 999❑Mane.verirjg 2 11 Partial

99rilnDrydock II 98fl Moored I I 3H Full Load 33.Time

42.1 mUtidetarminad2DH0avY Weather3n Fire4~ Flooding

%%::270 Vibra,ion~rshock

:9Lounchingor Drydo.kingCorgoShifting

10~ West.ge]1flExPlo. io.12DIC.313 D%uck Obiectin WCJt*r

CAUSE1

4’. ln Alleged 2 m Proven DISPOSITION1

43.1 D Repairedat Sea2 ❑TemporaryRepair3 ❑Part Repaired4 m Repairat Next For?5 ❑Repairat NcIxtDrydocki.g

F====44. PreviousRelatedFailure:

TYPE OF STRUCTURE I47.1 D Bulkhe~d(l.cl. stiffefiifig)

I

2 n Dack(lncl. stifftanimg)TYPE OF FAILURE

46.1 D Frocwre

~ ~ ~he~;~l. .+iff.ni.g)

5 D Floorsz D Buckling 6

B

From..3 H Deformation(Bulging, 7 Plating

Indentation,Setup) 8 stem4 D Crocks 9 n Star. Fmmne5 D B~.di. g 10 n Bilge Keels6 u F.ilumof Weld

~~ BHatchCoaming

7 D w6<tOga WebFrame,

i

IOther

REMARKS 54.

39”WaveLm.gth

40”WaveDirection

~ “—45-1 D Catastrophic-Ship I-$f

2 D Maiar- U.ableto proceed

3 ❑Minor- No delny-repair.ndnrwayorat next port

4 a Local - Repair.+ Convenience

LOCATION I Bott.mnBilgeTonktopSideWeatherDeckInteriorDecksup*r%truct”reForecastle

5’” TonkNos.

53-FramoNos. I

Fig.1 - SampleDataForm

.. -—.

5

Table1 - StructuralCasualtyDataBase

ALLEGEDCAUSE

CoUsiontitiVe8se{sNongsi~ ‘A”’Coil.isionswithPiersQuays

CollisionsWithLocks ~ **CollisionswithVesselsUnderwayMiscellaneousCollisions

{HeavyWeather,BottomSlamming

<HeavyWeather,ForecastleandWeatherDeck~eavy Weather,MiscellaneousGroundingStruckObjectinWaterIceWastageFireLaunchingorDryDocknngLoadingorDischargingCargoMiscellaneousUndetermined

NUMBEROFCASES

203179756627482317371478‘42

181086

PERCENTOFTOTAL

24,621.79.18.o3.35.82.82.14.51,71.01.01.01.02.2L2

10.4824 100.0

Unfortunately,informationonthedollarcostofdamagewasnotgenerallyavailable.Thefollowingdiscussionofthefrequency-of-occurrenceofaparticulartypeofdamagedoesnotincludecost.Frequencyaloneisnotnecessarilyameasureoftheseverityofdamage.

VarioustypesofcollisiondamagecomprisethelargestPortionofthetotalcases--67%.Heavyweathercauses,result-inginforefoot,forecastleandweatherdeck,orothermiscellane-ousdamage,arethenextlargestgeneralcategory--11%ofthetotal.Casesforwhichthecauseofstructuraldamagewasunde-terminedamounted,toalittleover10%,andtheremaining12%fellintoeightothercategoriesasshown.

Collisionswithpiers,quays,andotherfixedmooringstructurescomprise203casesor25%ofthetotal.TownsendandHamrinfounda similartrendfor100shipssurveyedoveraperiodofayear(MARINEENGINEERING/LOG7“ShipDamagell,p.51,Vol.LXVIII,No.11,October1963).Collisionswithlockscomprisedalittlelessthan10%ofthetotaldatabase.Shipsofsomedesignsdidnothaveanyreporteddamagefromthiscause,suggestingthattraderouteconsiderationsareamajorfactor.

—

6

Structuraldamagesustainedthroughcollisionswithothervesselsalongsidealsoconstituteoneofthemajorcategoriesofcasualties.Tugsassistingshipsduringmooringmaneuvers,lighters,cranebarges,andlandingcraftofvarioustypeswerefrequentlypartiesinsuchcollisions.AnumberofthereportedcasualtieshappenedinSoutheastAsiawherecargoshipswereunloadingdirectlyintolandingcraftandlighters.

Structuralcasualtiesofundeterminedcauseofthedata.Thesecasualtieswereallminorandrevealedinthecourseofroutinesurveys.

Thirty-sevengroumdings--4.5%ofthedataOfthese.31involveddeformationandbucklingof

comprise10.4%generallywere

--werereported.variousunder-

waterportionsoftheships,withonlysixcasesofholingorfracturingofbottomplating.In23cases,ofwhichfourinvolvedbowbulbs,onlyshellplatingdamageoccurred.Fivemorecasesinvolvedinternalstructuralmembersaswellasshellplating,andnineadditionalcasesincludeddamagetobilgekeels,plating,andinternals.Aboutone-thirdofthedamagedareaswerelooatedintheforebody,aboutone-halfaroundthemidbody,andtheremainderaft.

Threeothercategoriesofstructuralcasualtieswarrantbriefmentioninthissummary.Damagecausedbystrikingobjectsinthewater,forthemostpartwasconfinedtoships’bottoms(9outof14cases),indicatingthatthevesselseitherstruckanuncharteredobjectoractuallygrounded.Mostofthesecasesinvolveddeforma-tionandbucklingoftheshell,ortheshellandinternalstructuralmembers.

Structuraldamagecausedbyicewasrevealedduringthesurvey.Thetotalnumberofcaseswassmall(7)but,sincealloccurredontankers,thismaybeofspecialinterestrelativetoA~cticshipdesign.Itisworthmentioningherethat,withoneexception,damageattributedtoicewasfairlyextensive,involvingnumerousplatesonthesidesorbowand,inonecasebucklingofthemain~eck,internalbulkheads,andfracturingofframingandshell.

Withfomexceptions,thestructuraldamagewhichoccurredduringloadinganddischargingoperationsisofonlyincidentalinterest.Fourcaseswerefoundwherestructuraldsmageresultedfromfillingtanksunderpressure;threeoccurredontankersandthefourthona cargoship.Inoneinstancetheproblemwastracedtoaventball-checkvalvewhichwaspluggedwithrust;whethertheremainderresultedfrominadequateventsizeorthroughcarelessness,isnotknown.

Figure2showsthelongitudinalandverticallocationofdamageforallcasesandallshipsononetypicalprofile.Thetransverselocationisnotindicatedbutmostcasualtiesaffectedprimarilytheshellorcontiguousstructure.-Damageindicatedonthebaselineinthisfigurewasgenerallyduetoslammingandconcentratedatthecenterline.

. —

“ —.. .10 9 8 7 6 5 4 3 2 1 n

Fig.2 - LongitudinalandVerticalLocationofDamage,AllCauses- AllShips

TherelativelocalizationofshipdamageislistedinTable2. Thestatisticalcenterofdamageisforwardofamid-shipsandgenerallythedamageoccursintheoutboardportionsofthehull.ItalsoappearsthatcertaintypesofstructurearemoresusceptibletodamageasshowninTable3. Here58%oftheoccurrenceswereintheshellandstiffenersand19%intheframing.Table4indicatesthatthepreponderanceofcasualties(79%)resultedindeformation.

Table2 - GefieralDistributionofStructuralDamage

Polw 49% FORWARDCENTER 9% MIDSHIPSSTARBOARD 42% AFT

Table3 - DistributionofFailuresbyStructural

Elements

rypI?ofStructure13ulkheadDeckShellBulwarkFloorFramingPlatingStemBilgeKeelWebFrameRemainder

%Occurrence56

5832

1912121

34%40%26%

Table4 - DistributionbyTypeofFailure

TypeofFaihrreFractureBucklingDeformationWastageDeformationandBucklingDeformation,Buckling,andFractureDeformationandFractureCracks,Bending,WeldFailure,WireCutting,Holing

%Occurence31

7917153

8

STRUCTURALCASUALTYPROEIIEMAREAS

Analysisofthestructuralcasualtydatarevealedthreeareaswhichwarrantdetaileddiscussion.Whiletheseareasarenotintendedtobeall-inclusive,theyarepresentedtoindicatethevalueoftheprograminidentifyingandlocalizingproblems.Someneedadded~esearchwhileothersneedtobebroughttotheattentionofdesignersforrefinementofdesigndetails.Thesethreeareasarecollisiondamage,slammingdamage,andforecastleandweatherdeckdamage.

Some13specificshipdesignclasseshavebeenselectedforamoredetailedinvestigationofthesethreeproblemareas.ShipsofeachoftheseclasseshavesustaineddamageattributedtooneOTmoreoftheproblemareasasindicatedinTable5.

Table5 - ClassesofShipsSelectedforDetailedDamageAnalysis

Design

ABcDEFGHIJKMN

ShipsInClass

118845662

266512

DeliveryDates

1962-63196(F621961-631960-611964-661962-631962-631966

1960-651964-651961-65

19581961

ApproximateSpeed,Kts.

21191818212020231823201620

MachineryLocationMidshipMidship

AftMidshipMjdshipMidshipMidshipMidship

AftMidshipMidship

AftMidship

DAMAGECASESANALYZEDCollision SlammingWeather

48 14 430 1116 711 418 218 230 2

1145 331 116 1

7551

CollisionDamage

Tencargoshipdesignswereselectedforcollisiondamageanalysis.Shipsofthesetendesignswereinvolvedinalmost80%ofthecasualtiesrelatedtocollisionswithpiers,vesselsalongside,andlocks.

Threespecificfactorswereinvestigated:

1. longitudinalextentandlocationofdamage

2. verticalextentandlocationofdamage

3. ty-peofdamage.

The followingpa~agraphscoveranalysesofeachofthesefactors.

— —.. —-

9

100 90 80 70 60 50 4(I 3(I 20 ~fJ OPercentofLengthFromStem

Fig.3 - LongitudinalDistributionofCollisionDamage

Usingthesurveydata,andbasicinformationfortherespectiveshipdesigns,plotswerederivedofthelongitudinalextentandloca-tionofcollisiondamage.Collisionswithpiers,vesselsalongside,andlocksweretreatedseparatelyinordertoascertainwhetherchar-acteristicdifferencesexistedbetweenthesetypesofdamage.

Comparisonsofindividualshipresultsbycausedidnotshowanymarkeddifferencessotheywere-combined.‘Figure3showsthe

\ I r I

l+heer

1st

2nd

3rd

4th

I5th

6th

)Bilge~ 20 30 40

PercentofTotalPlates

Fig.4 - VerticalDistributionofCollisionDamage

._—

longitudinaldistributiofiof~amageduetostrikingpiersandquays,damagefromcolli-sionswithvesselsalongside,anddamageduetostrikinglocks.

Thedataforthesametenshipdesignsprovidedthebasisforanevaluationofver-ticalextentandlocationofdamagerelatedtothesamethreecauses.Informationfromthesurveydatasheetsonindividualdamagedplateswastabulatedforeachdesign.Thisinformationwasthentotaledandanalyzedtodetermingtrendsinverticaldistributionofdamage.Tables6,7,and8 summarizetheresultsforpier,vesselalongside,andlockcollisionsrespectivelyandtheresultsaredisplayedgraphicallyinFigure4.

ItcanbenotedfromFigures3and4thatthelongitudinalandverticaldamagedistributionsfromcollisionswithpiersand.locksaremarkedlysimilarwhereascollisionswithvesselsalongsideresultindistributionswithdifferentcharacteristics.Pierand.quaycollisionstendtocausesomewhatgreaterdam-ageatthewaterlinethandocollisionswithlocks. Lockcollisionstendtoproducemoredamagejustbelowthesheerstrakewhichisprobablyrelatedtoaccidentsoccurringwhenshipsareonthelow-watersideofthelock.

10

Table6 - VerticalDistributionofDamageDue

NumberofPlatesInvolvedPerStrake

toStrikingPiers

StralreBelowSheerSi,rakeDesign CasesperClass.

A 17B 16c 11D 8E 7F 9G . 19I 52J 10K 9

TOTALS x

PERCENTOFPLATES

SheerStrake 1st—

232

10 12

30 543

G Y6

9.6 1s.3

2nd 3rd 4th 5th 6th— —T ~8 71 -

22 16 l--11 10 l--18 26 l--

5 s2-5 ----272473

57 1 ~. 1195 ---

16.1 31.7 14.9 6.0 3.4

Table7 - VerticalDistributionofDamageFromVesselsAlongside

i!lumberofPlatesInvolvedPerStrakeStrakeBelowSheerStrake

Design CasesperClass SheerStrake 1st q: 3+ AS ~ 6_t+TumofBilgeA 13 1 -iBcDEFGI

.JK

TOTALS

115348

1160117

=3

2

51

13

9 46 28 4 - -4 15 16 4 - -12----.- 14––431----- 4 15 9 –91 14 SI 3 3 1623 70 44 7 - --- 252-.— —

G3GG 70 23 19

2

7

PERCENTOFPLATES 3.6 22.2 25.o 30.4 11,63.8 3.1 0.3

Table8 - VerticalDistributionofDamageDuetoStrikingLocks

NumberofPlatesInvolvedPerStr*eSt@reBelowSheer!Mrake

Desigu Casesperckss 8heerStrake 1st 2nd 3rd 4th 5th 6thA 18 7 —3 T To m-zB 3 254 ---E 7 7 71-F 1 1 3–---”–1 33 5 22 - 17 11–J 10

TOTALS T2

PERCENTOFPLATES 4.7 24.0 14,7 26.0 18.7 9.2 2.7

11

Thelongitudinalandverticaldamagedistributionsforcollisionswithpiers,quays,andlockshatiebeencombinedtoproducethecontoursofFigure5. Thesearecontoursofequaldamageprobability;theyarelabelledwithanarbitraryscalerangingfrom1to10,i.e.,fromlowesttohighestprobabilityofdamageintheregionofthehullalongthelinesofthecontours.Asimilarsetofcontours,basedondatafromcollisionswithvesselsalongside,isgiveninFigure6.

100 90 80 70 60 10 0

---=---~ \/-

1

Sheer

\\\= “-2-7zA\\- ?//// / 4th

1- -+/ II l“’-A” \——L -JBil,g~

$trake90 80 70 60 54 40 so 20 10

PercentofLengthfromStem

Fig.5 - DamageLocationProbabilityContoursFromCollisionsWithPiers,Quays,andLocks

100 90 80 70 60 w 40 M m 10 0

\90 80 70 60

Percent0[ LengthfromStem

Fig.6 - DamageLocationProbabilityContoursFromCollisionsWithVesselsAlongside

12

Table9 - FailuresResultingFromStrikingPiers

Design Total ShellDeformationShell&InternaiDeformation,Cases Only _Deformation Buckling

A 17 8 4 3

InternalFracture

Misc.Fracture

2BcDEFGIJK

TOTALS

1611879

1952109

E

561538

3355

E

115716

101043

G

. ———

— —

.

—

-o --i15

Table10- FailuresResultingFromStrikingVesselsAlongside

Design TotalCx

A 13B 11c 5D 3E 4F 8G 11I 60J 11K 7—

TOTALS133

ShellDeformationOnlv

7531368

45107—

95

Shell&InternalDeformation

44221

381

T5

Deformation,Buckling

11

ShellFracture

1

InternalFracture

Misc..J

—

—

—

1—

1—.—

T

5 1 1—

—

-7—

—3 3

Table11H FailuresResultingFromStrikingDesign Total ShellDeformatimShell&IntemalDeformation,

Cases Only Deformation BucklirrgA 18 11 5 2B 3 1 1 1E 7 4 3F 1 0 1I 33 10 21 1J 10 3 ~ —

TOTALS~ G 38 4

LocksShell

Fracture—

InternalFracture

Misc.

—

——

—o

— —1 0

TheShipStructureReliabilityDataSheet(Figure1)listsseventypesoffailures:fracture,buckling,deformation,cracks,bending,failureofweld,andwastage.Asapracticalmatter,agivencasemayinvolvemorethanoneofthesecategoriesincon-junctionwithoneormorestructuralmembers.Analysisofthefailuretypedataforthetencargoshipdesignsinvolvedsum-marizingtheoccurrencesofeachtypeoffailure,takingintoaccountthepracticalaspectsoftheproblemmentionedabove.Tables9,10,and 11 summarizetheseresults.

13

Ascanbeseen,thevastmajorityofthecases,regardlessofcause,consistedofdeformationofjusttheshellplatingortheshellplatingandinternalstruct~al‘embers”Indeed,outof363casestherewereonly26 casesinvolvingdeformationandbucklingofinternalstructuralmembersandonly8involvingfracturedstructures.Ofthe8 fracturecases,only3involvedshellplating;lessthan1%ofthetotal.

TherelatzveoccurrenceofcollisiondamagewithpiersinU.S.andforeignportswasinvestigated.ThirtyninepercentOf>. thecollisionswithpiersoccurredinU.S.portsand61%inforeignports.Whileamuchhigherpercentageofthesecollisions

“ withpiersoccurredinforeignports,onemustbecarefulnottomakeimproperassumptionsaboutshiphan~ingorpierconstmction~Forinstanteritwasnotpossibletod@terminetherelativeC~~herofportsofcallbetweentheU.S.andforeigncourrkmes.informationforcollisiondamagewasnotobtainedduringthesurvey.

HeaWWeatherSlammingDamage

Thetotalnumberofoccurrencesofbottomslammingdamageamountedto48.AlloccurredondrycargoshipdesignsasshowninTable12.Sincethenumberofcasualtiesfoundduringthesur-veywaslimitedbytheavailabilityofrecordsfromeachsourceofdata,thenumberofcasualtiesshowndoesnotnecessarilyrepresentalloftheoccurrencesofslammingdamagefortheshipdesignslisted.

ThelongitudinalExtentandlocationofslammingdamage,asa functionofshiplength,isshowninFigure7foreach~hipofeachdesign.Ingeneral,this@Pe ofstructuraldamage1scenteredatapproximately20%ofthelengthfromthebowandextendsasfarforwardas5%ofthelengthfromthebowandasfaraftas35%.Figure8 showsthedistributionofslammingdamagerelativetoshiplength.

Table12- SummaryofBottomSlammingDamage

Design ShipsinClass CasualtiesinDataBase

A 11B 8c 8D 4E 5F 6G 6H 21 26J 6K 5

TOTALS G

1411742221311

~8

CasualtiesperTotalShips

1.271,370.881.000.400.330.330.500.120.170.20

ShipsHavingCasualties

116532221311

0.55 37

CasualtiesperShipInvolved

1.271.831.400.751.00Loo1.00Loo1.001.00Loo1.30

.

14

DESIGN

m

40 30 20 10 0LocationofDamage- PerfientofLengthfromBow

Fig.7 - ExtentandLocationofSlammingDamageforVariousCargoShipDesigns

Themostprevalenttypeoffailurewasdeformationofhullplating,inparticulartheflatkeelandA-strskesportandstar-board.A smallernumberofcasesinvolvedadditionaldamagetootherstrakes,floors,andinternalstructuralmembers.Furtherdetailswillbediscussedinthetreatmentofindividualdesigns.

All 11 shipsofDesign‘A’encounteredslammingdamage,atonetimeoranother;a totalof14caseswerereported.TheyencounteredthereporteddamagewhileoperatingintheNorthAtlanticbetween1963and1966.Eightofthe11 shipssuffereddamagebetweenthemonthsofNovemberandMarch,oneinAugustandfortheremainingtwocasualtiesnodatesweregiven.FourofthecasualtiesinvolvedtheflatkeelandA-strakesportandstarboard,oneadditionalcaseinvolvedthekeelplate,A-strakesandfloors;theremaining9 casesinvolveddamagetocombinationsoftheflatkeel,floors,andshellextendingouttotheC-stra,ke.

15

,—-——” . ----- -——— -.. —. ~.

I

I

I

G

rJ....................................:...................*....

30 20 10PercentofLengthfromStem

Fig.8 - CumulativeExtentandLocationofSlammingDamage

ThebodyplanofDesign‘A’indicatesgenerallyU-shapedforebodysectionstypicalof~nY‘O‘“~argoship‘esi~sgFigure9 showsa sketchofthestructuralarrangementm theareaofinterest.Althoughdetailswerenotavailable,itwasascertainedthatallshipsinthisclasssustaineddamageofthetypedescribedaboveduringtheirfirstyearof.operation.Afterrecognizingthisslammingdamageproblem,addlt~onallongitudinalwereaddedonallshipsofthisclass.Nofurthercasualtieswereexperienced.

SixoftheeightshipsofDesign‘B’haveincurred11casesofslammingdamage.SixcasesofdamageresultedfromoperationsintheNorthAtlanticduringthewintermonths.!l?hreeofthecasualtiesoccurredintheSouthAtlanticdu~ingJulyandAWst(winter),oneoccurredintheIndianOceaninMarch,andthe.dateofonecasualtywasnotgiven.EightcasesinvolvedtheflatkeelandA-strakes?portandstarboard?twoinvolvedtheflatkeelaloneand,inonecasejusttheA-strake.In10 casesthehullplatingwasdeformedandonecaseinvolvedminorcrackingofthekeelplat@.

16

DESiGN‘B’

DESIGN‘D’

1 BO’ITCMPLATINGKEEL2 FLOOR3LONGITUDINAL4INNERBOTTOM5 CENTERVERTICALKEEL6FULLSIDEtiEELWN7 PARTIALSIDEKEELWJN8FLATBARSTIFFENER

4’ 5

DEWGN‘c’

Fig.9 - StructuralDetailsinAreaofBottomDamage

17

Figure9 showsa sketchofthestructuralarrangementsofDesign‘B’inthemajorregionof failures.Ovaraperiodofyearsstructuralmodificationsweremadetosomeoftheshipsinthisclassinordertoobviateslammingdamage.Detailsastoexactlywhatimprovementsweremade,andwhethertheyweresuccessful,havenotbeenascertained.

FiveoftheeightshipsofDesign‘C’sufferedsevensl~-mingdamagecasualties.SixofthecasualtiesoccurredintheAltanticandoneinthePacific.Fiveoccurredduringwintermonthsandtwointhesummerandfallmonths.Thelocationandextentoftheslammingdamageonshipsofthisdesiqisinte~est-inginthatitgenerallyoccurredalittlefartherforwardthanwasthecasewithallbutoneoftheremainingdesigns(seeFi@re7).Thecenterofdamageisapproximately16%ofthelengthfromthebowandisgenerallyconfinedtotheareabetween10%and20%ofthelength.

AllbutoneofthecasualtiestoshipsofDesign‘C’involvedtheTlatkeelandA-strakes,portandstarboard;theremainingcaseinvolveddamagetotheflatkeel.Allcasesresultedindeforma-tionoftheplating.Figure9showsstructuraldetailsinthisarea.Somestructuralmodificationshavebeenmadetoshipsinthisclassbutdetailsofthesemodificationsandtheirrelativesuccessinreducingslammingdamagewerenotfound.

Design‘D’comprisesfourcargoships,threeofwhichincurredslsxmningdamage.ThreeofthecasualtiesoccurredintheNorthAtlantic,twointhewinterandoneinApril;thefourthcasualtyoccurredinthepacificduringthewinter.Thelocationandextentofthisdamageisalsointerefltingsincedamagewasconfinedgener-allytotheforward10%to20%ofthelengthandconsistedprimarilyofdeformationoftheflatkeelandA-strsXes,portandstarboardintheareashowninFigure9. Noinformationwasobtainedregard-ingstructuralmodificationtotheseships.

Designs‘E’,‘F’,‘G’,and‘H’aresimilarandincurredslammingdamageonfrom30%to50%oftheshipsineachclass.TheslammingdamagetoDesigns‘Etand‘1?’occurredduringthewinterintheAtlanticand,toDesigns‘G’and‘H’,duringthewinterinthePacificandMediterraneanrespectively.SixofthesevencasualtiesinvolvedtypicaldeformationoftheflatkeelandA-strslces,portandstarboard,aswellasinternals;theseventh,onDesign‘G’resultedina fractureoftheE-strakejustabovetheinnerbottom.

Designs11’,lJ’,and‘K’incurredheavyweatherslammingdamageonlessthanone-thirdoftheshipsperclass,FiveofthesixcasualtiesoccurredduringwintermonthsineitherthePacificorAtlantic.ThreeofthecasualtiesforDesign‘I’involveddeformationofplatesinoneormorestrakesbothportandstarboard.ThetwocasualtiestoDesigns‘J’and‘K’involveddeformationoftheflatkeelandA-strake.

18

Designs‘A’through‘D’areclassesforwhichrea~onableproofhasbeenobtainedofsusceptibilitytodamagefromslamming.Foreachofthesedesignsallormostoftheshipshavesufferedslammingdamageatonetimeoranother.Mostprobably,ifmorecompleterecordswereavailable,additionalcaseswouldbeaddedtothosealreadyrevealedinthissurvey.

..Theremainingeightdesignsl‘E’through‘K’,apparently

fallintotwoadditionalcategoriesrelativetostructuralresist-ancetoslammingdamage.Thesecategoriesare:

Thosedesignshavingsustainedslammingdamage“butnottotheextentthattheycanreasonablybeconsideredasbeingstructurallydeficient(Designs‘E’,‘F’,‘G’,and‘H’);

● Thosedesignshavingsustainedslammingdamageunderextenuatingcircumstanceswherestructuralsufficiencyisdifficulttoevaluate(Designs111‘J’,9 and‘K’).

Furthermonitoringofstructuralcasualtydatashouldprovideagreaterinsightintotherelationshipbetweenstructuralsufficiencyandsusc~ptibilitytodamagefromslamming.

P~ecisedetailsastothecircumstancesunderwhichthecasualtiesoccurredarelacking.Othe~thanthefactthatthemajorityofthecasesoccurredduringwintermonthsonvarioustraderoutes,littleadditionaldatacouldbefound.Shipspeeds,loadingconditions,andotherenvironmentaldetailsatthetimeofthecasualtieswere,inmostinstances,eitherunreportedorstatedinveryqualitativetermssuchas“mountainousseas”.

Noneoftheslammingcasualtiesresultedincatastrophicor‘unabletoproceed’damage.Indeed,mostofthecaseswereminortotheextentthatsomeoftheshipswerenottakenoutofservicespecificallytorepairthatdamage.Somecostdatawereobtainedintheinstanceofslammin

idamagetoships.The

averaecostofrepairswasfoundtobef

27,700witha spreadfrom4800to $68,700.

HeavyWeatherDamage.Forecastleand.Weather.Deck.Thenextmostprevalentformofheavyweathercasualty

lmcoveredduringthesurveywasdamagetostructuralcomponentsontheweatherdeck.Outof23cases17occurredintheareaoftheforecastleandtheremainderatlocationsfartheraft.Mostinvolveddamagetobulwarksandsometodecksandinternalstructuralmembersaswell.

Table13 summarizestheinfo~mationforsixspecificdesigns.AllofthedesignsarecargoshipswiththeexceptionofDesign‘Mlwhichisa tanker.

19

Table13- SummaryofWeatherDeckDamagesinHeavyWeather

Design NumberofShips Numberof NumberofShipsHaving LocationinClass Casualties Casualties ForecastleAft

.1 6 7 4 6 -iii 5 5 3 5M 1 5 1 5–A 11 4 3 1 3G 6 1 1 1N 2 1

TOTALS T1 %1

T7 ‘6

Fourofthedesignswarrantfurtherdiscussion.FourofthesixshipsofDesign‘J’hadatleastseven

casualties,sixoccurringontheforecastleandoneinvolvingbulwai-ksfartheraft.Thetypesofstructuralfailuressympt-omaticofthisdesignare:

1. forecastledecktornordeformed;2. bulwarkandbulwarkbracketsandstiffeners

fractured,buckled,anddeformed;3. internalbeams,longitudinal,and

framesdeformedorfractured.

Mostofthisdamageoccurredwithintheforward20to30feetoftheforecastleintheregionshowninFigure10.

ThreeofthefiveshipsofDesign‘K’sustainedatotaloffivecasualtiesintheforecastlearea.l?orthemostpartthedamageoccurredinanareabetween6feetand35feetaftoftheforecastlehead.Bulwarkbracketsandkneesaswellasdeckplat-ing,deckbeams,andgirdersweredeformedorfracturedintheareashowninFigure10.

Design‘M’isa tankerwhichhashadfivestructuralcasual-tiesintheareaoftheforecastle.Threeofthecasesinvolvedonlyfracturingofbulwarkbrackets.Onecase,howeveryincludeddeformationandfractureofthebulwarks,deckplating,andinte-rnalstructuralmembers.Inthisinstancethebulwarksweresetoutandthedeckplatingwassetup,indicatingthatforthiscasualtythedamageresultedfrommovingwatertrappedontheforecastle.Theremainingcaseinvolvedfracturedanddeformedhullplatesinthevicinityofthehawsepipebothportandstar-board,Figure10alsoshowstheforecastlearrangementofthisship.

20

Design‘J’

—.

“u-Fig.10

DeE@‘M’

- ArrangementofForecastle

21

Design‘A’alsosustainedweatherdeckdamagewhichisofinterest.Threeofthe11shipsinthisclasshadatotaloffourcasualties.Onecasualtyinvolveddamagetotheforecastleandappe,a?stobeanisolatedinstance.Theotherthreecasualties,however,involveddamagetobulwarksmuchfartheraft,byhatchnumbers3,5,and6. Inoneinstance60feetofbulwarkwastornawayandmissing;inanother30feetofbulwarkwasseriouslydis-tortedalongwiththefracturingofanumberofbulwarkbrackets.Sincesidebulwarkdamageocmrredrelativelyinfrequentlyand,sinceone-halfoftheoccurrenceswereonshipsofthisdesign~itissuspectedthatthebulwarkarrangemento-nDesign‘A’ismarginallyadequateatbest.Figure11showsa sketchofthebul-warkstructuraldesignforthisshipintheareawherethedarnageoccurred.

~8;’x3%’’x16#L

m

\\\

+

\\ Fig.11- SketchofBulwark,Design‘A’\

;’12.75#ll!I

‘bJ====-FShell

INTERPRETATIONOFSTRUCTURALCASUALTYDATA

Inthelimitedsurveyofshipcasualtiescoveredbythisreportitisnotpossibletoextractallofthemeaningfulinfor-mationwhichmaybecontainedintheaccumulateddata.Yettherehaveevolvedanumberoftrendswhichgivesomeinsightintowhatmaybelearnedbymoreexhaustiveanalysisofthesedataorfrommoreextensivesurveysofthistype.Additionallythelimitedanalyseswhichhavebeenmadecanbeinterpretedtoindicatealogicalpathtofollowinfutureresearch,development,anddesignyrojectsaimedatimprovedshipstructures.

Firstitisimportanttorememberthata shipcasualtyinvolvesbotha causeandaneffect--andthetwoarenotalwaysseparable.Furthermorebothcauseandeffectmayeachcompriseanumberoffactorsrelatedtotheenvironment,operationaltech-niques,economics,andchance,aswellastothemanycomplexelementswhichenterintothedesignofamodernmerchantship.

22

Anyinterpretationofshipcasualtydatawhichhasasi’t~goaltheimprovementofoneaspectofshipdesign,suchasshipstruc-tures,mustnecessarilytakeintoconsiderationallofthefactorsinvolved.

A cogentexampleofthiscauseandeffectrelationshipisfoundinanalyzingstructuraldamageresultingfromcollisions.Acollisionmaybecausedbyenvironmentaldisturbancesoverwhichnocontrolcanbeexercisedsuchashighwindorunexpect-edlystrongcurrent.Itcanbecausedbyimpropershiphandlingbythecrew,bypilotsanddockmasters,orbythecrewsofvesselsalongside.Thecausemayalsobelaidtothedesignerandbuilderwhoprovideinadequatemaneuveringcontrol,ortomalfunctioningofcriticalequipment.

Theeffectofa collision,asfarasthisstudyisconcerned,isdamagetothestructureoftheship.Thepertinentquestionisthenwhethertheshipstructuraldesignercandoanythingtoamelioratethedamageresultingfromcollisions.Thesurveydatacanbeinterpretedtoshowthat,tosomeextent,hecan.ReferringbacktothecontoursofdamagelocationprobabilitygiveninFigures5and6itispossibletomakesomeobservationsrelatedtothecauseandtheeffectofthecollisionswhichproducedtheseresults.

Collisionswithbothfixedandmobilestructurescauseddamagemostfrequentlyintheregionoftheloadwaterline.Colli-sionswithfixedstructuresalsoincurreda fairamountofdamagejust”belowthesheerstrake;boththewaterlineandabove-waterlinedamageconcentrationscenteredprimarilyatone-thirdofthelengthandsecondarilyattwo-thirdsofthelengthfromthestern.Theseconcentrationsofdamagelocationcouldindicatethatcollisionswithfixedstructuresoccurredmostoftenwhentheshipsweremovingforwardandthatcontactwasmadeintheregionofmaximumhullcurvature.Damagefromcollisionswithvesselsalongsidecenteredinaboutthesameregionofthewaterlineforward,buttheafterdamagecenteredatabout80%ofthelengthfromthestem.Alsodamagefrommobilestructuresoccurredwithgreaterfrequencyaftthanforwardindicatingthateitherthedamagedshipwasmovingasternorthattheotherpartytothecollisionwastheculprit.Itmightbementionedthatthisafterdamagecenterisa favoredregionforpushingwithtugswhenmovingawayfromapier.

Theforegoingdiscussionrelatesprimarilytoa surmiseofcausativefactorsincollisionsasindicatedbythesurveydata.Ontheotherhandthesedamagelocationprobabilitycontourscouldbeinterpretedasevidenceofa fa,ilureoftheshipstructuretowithstandcollisionswithfixedandmobilestructures.Bothsetsofcontourshaveamarkedsimilarityinthisrespectinthatthedamageoccurredmostfrequentlyattheweakestpointsofthehullstructure.

A conventionalhullgirderisdesignedwithmajorstrengthmembersalongtheupperandlowerextremities,i.e.,themaindeckandsheerstrakeandthedoublebottomandbilgestrake.Midship

23

shellplatingisdesignedheaviertoresistbending.aftpeaktanks,withtheirheavyinternalstructures,greatdealofstrengthtotheforwardandafter5*ofIfthistotalstren.dhpatternissuperimposedonthe

Theforeandprovideathelength.contoursof

I?igures5and6it;an~eseenthat~hep;ohabilityofsustainingdama,geisinverselyproportionaltothestrengthofa conventionalhulldesign.

Whetheritiseconomicaltoattempttodesigna shipstructuretoresistoramelioratedamagefromcollisionsissomewhatquestion-able.Howeverthedataobtainedinthissurveywouldindicatethatifsuchanattemptismadeitwouldlogicallyincludeinstallationofstringersalongtheshellatthewaterlineandwebframesintheregionsofone-thirdandthree-quartersofthelengthfromthebow.

Althoughdesigntoreducecollisiondamagemaybeopentoquestionthereappearstobenodoubtthatstructuraldesigntoreduce”heavyweatherdamageismandatory.Thisappliesbothtoslammingdamageanddamagetotheforecastleandweatherdeck.Thebasiccauseofheavyweathercasualtiesisobviouslytheenvironment.Theoperatorhassomecontroloverbothcauseandeffect;hecanreroutetheshiptoavoidheavyweatherandhecanslowdowr””tolessenthechanceofsustainingdamage.Howeverbothofthesecontrolmeasureshaveaneconomicconnotationinthattheyinvolvethelossoftimeanda correspondingreductionofrevenue.Thusitdevolvesuponthedesignertoprovidea vehiclewhichoffersmaximumprotectionagainstheavyweatherdamage.

Thelikelihoodofslaniningandoftakinggreenwaterovertheforecastleandweatherdeckisalsorelatedtothehullformandtheconfigurationoftheabovewaterbodyoftheship’.Weatherdeckdamagecanalsobeavoidedtosomeextentbytheerectionofprotectiveharriers.Ifitisassurriedthatevery-thingpossiblehasbeendonetominimizethehydraulicimpactsitthenisnecessarytoprovidea structuretowithstandtheloadingswhichmaybeimposed.

Thesurveydataalonedonotrevealmuchinformationonwhatcanbedonestructurallyasapalliativeforslammingdamage.Howevertheydoshowthespreadoffrom10%to30%ofthelengthoverwhichthedamageextendedandthatdamagewasgenerallyconfinedtotheflatkeel,A-strekes,andfloorsinthisregion.Thisshowsthelimitoftheareaoverwhichstruc-turalstrengthmightbeincreased.Furthermore,ifdetailswereavailableonthemodificationsmadetoDe-sign‘A’,itwouldbepossibletopointtoonestructuralarrangementwhichapparentlyprovidedsatisfactoryresistancetoslammingdamageononecla,ssofships.

Fromthemeagerdataavailableonforecastledeckdamage,onlytentativeconclusionscanbedrawnastowhatstructuralmodificationsmightbewarranted.Ap~rentJyconventionalbul-warkstructuresareadeqwatetowithstandthehydraulicimpactincurredasthebowpitchesdownward.Themajordamageseemstohavebeenincurredaftergreenwaterengulfedtheforecastleon

24a down-pitch;asthebowlifted,theupwardaccelerationofthemassofentrainedliquiddevelopedforceswhichdeformedtheforecastledeckandloweredthebulwarksoutboard.

Apparentlythedeckdrainageaffordedbyline-handlingopeningsinthebulwarkisinadequatetocopewiththisproblem.Oneinterpretationmightbetoeliminatethebulwarkandprovidea considerableamountofcambertotheforecastledeck.Ifthebulwarkisrequiredasa sprayshieldinlesssevereweather,itmightbereplacedbyrowsofspray-deflectingslatswhichwouldpermitmorerapiddrainageoftheforecastle.Thesameapproachmightbeconsideredinareas”ofthemaindeckabafttheforecastletoprovideprotectionfordeckcargo--particularlyinthecaseofcontainerships.

Theinstancewherea tankerincurreddamagetoplatingandstructurearounditshawsepiyepromptsaprecautionarynoterela-tivetostructuraldesigninthebowregion.Arigidelementsuchasthiscancreateahardspotwhichrestrictsflexingofthestructureinresponsetoheavyweatherimpacts.Thiscanresultinlocalizeddamageintheareawheretherigidelementisattached.Excessivestiffeningoftheforefootortheforecastledeckcouldhavea similarlyundesirableeffect.CONCLUSIONS..OTllREC!ONDD3NDATIONS

Ithasbeenshown,evenfromthelimitedquantityofcasualtydataobtained,thatsignificanttrendsofstructuralfailureareevident.Fromthedataevaluatedinthissurveyithasbeenpossibletodrawa fewconclusionsastodamagerelatedtoheavyweatheratseaandtherelativesusceptibilityofvariousshipstructurestodamagefromcollisionswithfixedandmobilestructures,

Althoughthesetrendsaresignificant,theyhavenotyetbeensufficientlyvalidatedtorecommendandjustifyspecificstructuralmodifications.Itisbelieved,however,thatamorethoroughexaminationofthecasualtieswhichproducedthesetrendswouldbeofvalue.Particularlyincasesofslammingdamage,andtoalesserextentcasesinvolvingdamagetotheforecastleandweatherdeck,itwouldbepossibletoattaina betterunderstandingbyfurtherexaminationoftheenvironmentalconditionsandofthehullformandabovewaterconfigurationinthebowa,reaofeachshipinvolved.

IncasesofcollisioncasualtiesitappearedthattheWmagecenteredintheweakerregionsofthehullstructure.~t thesedamageconcentrationswerealsologicallyrelatedtooperationalfactorsassociatedwithshiphandlinginrestrictedwaters.Theunderstandingofcauseandeffectincollisioncasualtiescouldbema,rkedlyimprovedbyaddingmoretankercollisioncasualtydatatothedatabase.Thelongitudinalframingoftankersappearstobeinherentlymoreresistivetodamageofthistypeandthus,ifstructuralchangescanindeedreducetheextentofcollisiondamage,thiswouldbecomeapparentInanalysesofsnchanexpandedcollectionofdata.Suchaddi-tionaldataontankercasualtiesareavailableinthefilesoftheU.S.SalvageAssociation.

25

Anystatisticalsmaryofamassofdatahasbotb.advan-tagesandlimitations.l’hestatisticalapp~oachcanaidinpointingoutareasofdamageattributabletospecificcausesandthephysicalextentofsuchdamage.Thegreaterthemassofdatathemoreistheauthoritywithwhichthefingercanbepointedatareasofdeficiency;thusthereisa strongtendencytoperpetuateanydatacollectionandanalysisprogram.However,inthispar-ticularcase,itisbelievedthatcontinuationiswarranted.Atpresentitisevidentthatthedatacollectionandanalysispro-gramhasyieldedinformationofspecificvalueasrelatedtocertaintypesofstructuraldamage.Withtheassimilationofadditionaldataitwillbepossibletolearnmo~eaboutthesespecifictypesofdamageandtoisolateothertypesofdamagewhichoccurfrequentlyinvariousclassesofships.

Thedatafarm,Figure1,derivedasapartofthisstudyisgenerallyadequatetorecordthemaximpmamountofinformationavailablefromknownsourcesofcasualtydata.Althoughtheformprovidesfornumerousentriesrelatedtotheextentofdamage,theapplicableinformationisseldomprovidedincasualtyreports.Oneadditiontotheformissuggestedwhichwouldmakethedatamoremeaningfulinthisregard--thecostofrepairs.Costwouldbeusednotasaneconomicindexbutasananalyticalweightingfactorasameanstoassesstheextentofdamage.

Itisalsoconcludedthat,whilestatisticalanalysesoftheaccumulateddataarevaluableandshouldbecontinued,theultimateworthofstudyingcasualtiesishighlydependentuponanengineeringevaluationofallcasualtysituations.Fromadesignviewpointitisessentialthatcauseandeffectbeisolatedandcategorizedsoastodeterminewhataspectsaredesignf~ctionsandwhataspectsareoutsidetherealmofthedesigne~.Inthissensethedesigner’srealmincludessuchelementsaspropulsionandmaneuveringcontrol,hullconfigura-tion,andarrangementsaswellasthehullstructureitself.Thesedesignelementsareallinterrelatedintheperformanceofa shipandmustbetreatedtogetherwhenexamininghowtotalperformancecanbeimprovedbothtechnicallyandeconomically.Thuscasualtydataanalysesshouldbeundertakenbycompetentengineerswhoareawareofalldesignelementsandwhohaveareasonableunderstandingofthemanycomplexitiesofshipopera-tion.Whenexaminingcasualtydatatheyshouldhaveaccesstopertinentdesigndetailsoftheshipsinvolved,includinghulllinesandmachineryarrangementsaswellasstructuralplans.

A finalrecommendationonthecontinuedcollectingandanalysisofshipcasualtydataisthattheprocessbeexpandedtoincludealldataavailableforthelastfifteenyearsandthattheprocessthenbekeptcurrentasnewcasualtiesoccur.Inthiswaya solidbaseoffundamentaldatawillbeinhandagainstwhichnewdatacanbecompared.Itthenmaybepossibletospotdeficienciesinspecificshipdesignsintimetorecom-mendcorrectiveactionwhilethoseshipshaveusefulliferemain-ing.Furthermore,overanextendedperiod,itwillbepossibletoevaluatethesuccessorfailubeofspecificmodifications.ThiseventuallywillprovideapowerfultoolforimprovingtheeconomicperformanceofshipsoftheU.S.Merchantfleet.

UNCLASSIFIEDSecurityLmssltlcarm

DOIWMENTCONTROLDATA- R&D~securitY ~lassificationOf rim, body ofab.trucf arm’ ind.xind ~nnofa!f~n .IUS! bc e~!-d when tjle overall reportis rl==ified)

OR,G, NATING ACTIVITY (cOtPOrateAUthOr) Za. REPORT SBCURITv CLASSIFICATION

RobertTaggartIncorporated UNCLASSIFIED3930WalnutStreet 2b. GROUP

Fairfax.Virainia77030REPORT TITLE

A LimitedSurveyofShipStructuralDamage

DESCRIPTIVE NOTE=. {Type of report and inclU*ive date=)

FinalAU THOR(SI (First name, middle initial, Iaslnamm)

SethHawkinsGeorgeH.LevineRobertTaggart,RobertTaggart,Inc.

REPORT DATE 7n. TOTAL NO. OF PAGES 7b. NO. OF flEFS

August1971 25CONTWACT OR GRANT NO. 9a. ORIGINATOR’S REpORT NuwBEe(s)

NOO024-70FC-5214,.PROJECT No.

RT-29406

ShipStructureCommitteeResearch“ Project,SR-189 gb. OTHER REPORT NO(SI (AnyOtherntimbe,.th=tm.v@ .-ef~ned

this report)

SSC-220r. I

b.DISTRIBUTION STATEMENT

Distributionofthisdocumentisunlimited.

1. SUPPLEMENTARY NoTES 12. SPONSORING MILITARY AC Tlv17Y

NavalShipEngineering’CenterNAVSECCode6132

A limitedinvestigation,conductedtodeterminetheavailabilityofdataonshipcasualtiesinvolvingstructuraldamage,revealed824applicablecases.A methodwasdevisedforreducingreportedcasualtydataintoa formatadaptabletoautomatictabulationandanalysis.Collisionwithfixedandmobilestructureswasfoundtobethepredominantcauseofstructuraldamage;heavyweatherdamagetotheforefootandforwardweatherdeckalsooccurredwithsignificantfre-quency.Patternsofdamagefrequencyandlocationexistedona numberofclassesofships.Thesehavebeeninterpretedtoindicatehow structurescouldbealteredtoreducethedamaqesustained.Recommendations,aremadetocontinuethedata-collectionextensivelytheinformationcan

andanalysisprografiandtoinvestigatemorewaysinwhichsignificantstructuraldesignbeextracted.

)DiW:.,1473 ~PAGEl) UNCLASSIFIEDS/N o1OI.8O7.68O1 SecurityClassification

UNCLASSIFIEDSecurityClassification

4.KEY WORDS

Ship

Ship

Structure

StructureReliabilityAnalysis

LINK A

ROLE WT ROLE

ID ,’:::,,1473’(BACK) 46n40 UNCLASSIFIED

WT

—

LINK C

ROLE

—

WT

(PAGE 2) SecurityClassification

SHIP RESEARCH COMMITTEEMar time Transportation Research Board

National Ac(demy of Sciences-ilational Research Council

The Shi~,Research Committee has technical cognizance of the i.tpr-agencyShip Structure Commi ttee’s .esearch program:

Advisory Grou~ 11, “Ship Structural Design” prepared the prolect prospectusand evaluated the proposals for this project:

The SR-189 Proje(t Advisory Committee provided the liaison technical guidance,and reviewed the project reports with the investigator:

MR. A. E. COX, Chairman, ,5:wi.oYi“rograrnJiznager, NezaportP?atisShipbuiM LW 4 DFy Dock Ct~.

MR. J E. tlERZ,ChiefSixu,tural Design Enginee?, Sun Shipbuilding & [)ryDock Co.

MR. H. S. TOWNSEND, vice Resident, 11.S. Salvage Association, inc.

SSC-207 ,

SSC-208 ,

SSC-209,

SSC-21O,

SSC-211,

SSC-212 ,

SSC-213,

SSC-214,

SSC-215,

SSC-216,

SSC-217,

SSC-218,

SSC-219 ,

SHIP STRUCTURE COMMITTEE PUBLICATIONS

Y“’hesedoczmzvzts are distributxd by the I?cztionalTechnics 1-TnforrnationService, Springf.ield, Va. 22131. Y’hcsedoe-

unents have been Gnnouneed. in the Clearinghouse e journn Z

U.S. Government d~:seareh & Development Reports (US(;17D!7)under the indicated AD numbers.

Effect of Flame IX i Mechanica Z straigh cening on Ma teriaZ Properties

o.f WeZdments b.y H. E. Pattee, R. M. Evans, and R. E. Monroe. 1970.Ab 710521

Slamming c>fShips: A Critical Revieu of the Cwmvi t.Stat? of k%Zedga by J. R. Henry and F. C. Bailey. 1970. AD 711267.

Resu 1t,:from FuZ 1-Teal.eMeasurements <If-Midship Bc?nd’ingStressesThree Dry Clwgo S)I@ by 1. J. ldalters and F. C. Bailey. 1970.AD 712183.

Anullysis of Slmi~g Data from the “S. S. Woluerine State” by JWheaton, C. H. Kane, P. T. Diamant, and F. C. Bailey. 1970.AD 713196.

,%sign 6 TES tia1lation of a Ship ReqxvLse ~n~tnummtation systernAboard the Contai?z?r Vessel “S. S, Boston “ by R. A. Fain, J. Q.Cragin and B. H. Schofield. (To be published)

%ip Response .k+twmenta.tion Aboard the Conf;ai?wz,Vessez “S. S.BOSLO??’l: ]?CSUZtS From the 1st Operational Season in North A tlantieservice by R. A. F~in, J. Q. Cragin, and B. H. Schofield. 1970.AD 712186.

A (hcidefor lJZtPas>nic Testing and Eoaluaiion of WeM Flati::by R. A.Youshaw. 1970. Al 713202.

(To be published).

COrmpre s s i 7>e s tr,(?WJ ?h”

PZates by H. 8ecke ‘,AD 717590.

(Y(ZCP. Plwpag dim ml AITest in s}iip and other SL:{Z Ls by G. T. Hahn,R. G. Hoagland, E’. N. Mincer, A. R. Rosenfield, and !1. Sarrat.e. 197i,