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