CATAMARANS-TECHNOLOGICAL LIMITS TO SIZE …

1 ,.-SSC-222 CATAMARANS-TECHNOLOGICALLIMITSTOSIZEANDA PPRAISALOFSTRUCTURALDESIGNINFORMATIONAND PROCEDUREST hisdocumenthasbeenapprovedforpublicrelea seandsale; -. ------- , ,largeplatform, ,ShipStructureCommittee . SSC-222 FinalReportonProjectSR-192, CatamaranDesigns , ; , ,axialforce,shear,andtorsionmoment~. , ,.. , ,.. ,,..,. (8),THESTRLIC-TURALDESIGNOFTHEASRCATAMAR ANCROSS-STRUCTURE , SUMMARYANDDISCUSSION OFREF~R:..ENCE(13), AMETHODFORESTIMATINGLOADSONCATAMARANCROS S-STRUCTURE ,..62iii Table1234567891011121314 LIST(IFTABLESPageCATAMARANLOADANDSTRUCTU REANALYSIS.,.. ~l ASR , *VERSLISA, *VERSUSL, * ;;VERSUSA, , , , ,SERIES60, ! ! STRESS ,.. ,..,..44..vSHIPSTRUCTURECOMMITTEETheSHIP STRUCTURECOMMITTEE isconstitutedtoprosecutearesearchprogram toimprmmthehullstructuresofshipsbyanexte nsionofknowledgepertainingtodesign, ,III,USCG,ChairmanChief, , , ,VicePresidentMilitarySealiftCommandAmer icanBureauofShippingSHIPSTRUCTURESUBCOMM ITTEETheSHIPSTRUCTURESUBCOMMITTEE actsfortheShipStructureCommitteeontechni calmattersbyprovidingtechnicalcoordinati onforthedeterminationofgoalsandobjective softheprogram,andbyevaluatingandinterpre tingtheresultsintermsofshipstructuraldes ign, , , , , , , ,LiaisonSOCIETYOFNAVALARCHITECTS& , , ,RCNC, , ,LiaisonLISTOFSYMBOLSW hereequationsarereproducedfromreferences , ])

2 FScFslFso9 HRI/~HLHRhLMlM= +ructureGravitationalaccelerationWavehei ghtSignificantwaveheightcross%ructureand huIIatiunctureofcross-structureandhul1,S idehydrostaticforceonoutboardshelISidehy drostaticforceinboardshelIHorizontalshif tofcenterofbuoyancyofonehulILengthbetwee nperpendicularMaximumverticalbendingmome ntatiunctureofcross-structureandhullMome ntatiunctureofcross-structureandhulIduet oweightofcross-structureMaximumwave-indu cedbendingmomentoncross-structure,weight -1esscross-structureMaximumaxiaIforceCle arhullspacingviiSymbolT1 TcTotDefinitionMaximumtorqueoncross-stru ctureabutitstwistcenter,t#oMaximumtorque oncross-structureaboutitstwistcenter,t=o LongitudinaldistancebetweenshipLCGandcro ss-structuretwistcenterCentroidofHLbelow neutralaxisofcross-structureCentroidofHR belowneutralaxisofcr~ssstructureTotalwid thofcatamaranWavesurfaceabovestilIwaterl ineatoutboardshellWavesurfacebelowstillw aterlineatinbcardshellTotal(bothhulls)di splacementgxaddedmassinswayofbothhullsWa velengthLCAM assdensityofwaterCircularwavefrequencyvi ii.

3 ,references(1)and(2).However,inthiscentu ry, ,suchasferries,oceanographicresearchship s,fishingboats, ,itispertinenttonotethattheseshipsareund er315feetinIengthlexceptfortwo,the400-fo otDuplus(Dutch)andthe425-footKyorOgly(Ru ssian).Itmayberecognizedthatforthespecia lpurposesinquestion,catamaranswereselect edovermonohullsmainlytotukeadvantageofth elargedeckarea,hightransversestabiIity, , whynotlargecatamarans? , ,theMaritimeAdministrationbeganwiththeCa tamaranStudy(1)1performedbyGeneralDynami csrandtheNavyhasunder-takenacomprehensiv eassessmentofcatamarantechnology(2),(3)a nd(4).LittonIndustriesclaimanactualdesig nofasemi-submergedcatamarancontainership (~)and(6),andFisher,etal,havepreparedapr eliminarydesignofacatamarancontainership fortheTrans-Atlantictrade(7). ,appraiseexistingdesignprocedures, ,crossstructurescant!ingslimitations.,co nstructionproblems,repairfacilities, ,viz:(a)AssemblyandcomparisonofalIavaila blemodeltestdataontheloadsonthecrossstru cture;(b)Evaluationoftheanalyticalmethod sforestimateofcross-structureloadand(c) (column-stabilizedorstrut-stabilized).

4 , , ,inprinciple, ,thattherewilInotbespecialproblemstoover come, , ,,featuresconsideredinreachingtheforegoi ngconclusionareasfollows:Resistance-Powe ring- , ,thisneednotsetanupperlimittothecatamara nsize,assumingthathullbeamissufficient, ,Cross-Structure$cantlingandStructuralMa terial:Thehydrodynamiceffectuniquetocata maransandofprimeconsiderationis,ofcwrse, thedifferentialwaveloadingonthehulIstobe absorbedbythe! ~< ,themaximumsteel(100,000psiyield)plateth icknessis1-1 :existingcargopiersaroundtheworldsuggest draft1imitationofExistingUnitedStatesdry dockfacilitiescunbuilduptoapproximately1 050 x140 snewdrydackatSparrowsPoint,Marylandwillm easure1200 x200 ,OnemilIiontondrydocksunderconstructioni nJapanandNorthernIrelandwiIIbeapproximat ey1965 x329 . ,iustthecorrectdepthandiustthecorrectwid th,maybeananswer, , , ~ITheLivingstonShipbuildi~gCompanyhasChy dockddthe10~ ~cksplitintotwolongitudinalhlalv$sheldto getherbyspacerbeams.\~;IIIi I11 IIII tisbeli~vedtha~theRus~ianshaveaschemefor !

5 ,1:1 1)f .~CargoH6ndlirigandPiers:\,,I,, ,atap~ice,iftheecolnornicsofcatamaranswe resoattractive~.Useoftwinpiersordi+chqrg eo~ :,,ICertainur!publishe~st~dies claimthattheworldc~n~cckpt1000 x400 1,! ,1I :I 1 1 IITheGeneralDynami~sstudy(1)andcertairlm aiorityofmaiorharborsaroundtheI,!1 I1:!, I/,, unpublishedstudiesclaimthattheeco-1,. , sfindingstodate(3)4states Nocompellingreasonisyetinsightforagenera lshiftfromthemonohulltothemultihullorcat amaranconfiguration. ~ TheStructuralDesignoftheASRC atamaranConstruction byLankford(8) ,therearetwophasestothecross-structurede sign,namely, (lightshipweightanddead-weight) , , 1C1--p3! , , ,ii,andiii,groundinganddockingloads(ifgr oundinganddockingiscon-sideredadesigncri teria) (9)(reportunpublished) (v)and(vi) ,atthispointitmaybedesirabletopointoutth attheproiectinvestigators conclusionsastothevesselpositionswithres pecttothewaves* ~ .. , , +-1---+i-+++1-1-++++ , ,Scottproposedexpressionsforthestressesd uetotorqueandtransversebendingofacata-ma rancross-structure(10).

6 Theyareasfollows:Torsion:Toobtainthetors ionalbendingvesselwaspoisedobliquelyonat rochoidalwuve,moment,afine-1ined300-foot long170 x1(3 .Thecrestcoincidedwith8theforwardquarter pointofonehullandtheaftquarterpointofthe otherhull,withthetroughattheextremities. (Scotthasnotprovidedadditionalinformatio nonthevesselorthebasisforselectinga10-fo othighwave.)Underthisattitudeofthevessel , , ,A=TotaldisplacementofcatamaranAssumingt hewingstructureasathinwalledrectangulart ubeintor-sion,thestress,S, ,assimpleasitmaybe, \0higher,inallothercases, :[ Hullseparationx1/2displacementofonehullS ectionmodulusofcross-structureoncenterli ne(W-2B)~/4=s6/4 SectionmodulusSectionmoduIusAportionofTa ble7isacomparisonofbendingmomentsgivenby S2/4withavailablemodeltestresults.[tshow sthatthetestvalueforASRishigherthanSL/4w hileforothervesselsSL/4ishigherthanthete stvalues.(Note:HereS=clearhullspacing).. 9 EventhoughScott , swell-knownandvaluablepaper, TheStructuralDesignofASRC atamaranCross-Structure (8) [.)]]]

7 (11),oceanwavespectrumderivedfromdataon1 2mostseverestormsattheNationallnstituteo fOceanography(GreatBritain),andwavefrequ encyoccurrenceintheNorthAt[ ~rtofthepaperwhichcoverspoints(ii)throug h(v)mentionedabove,togetherwiththerefere nces, ,thedesigntorqueisgivenbybd/4= , , ,namelytheASRandtheT+GOR16,10 However, , , sandDinsenbacher sworks(12)and(13)areconsideredto-gethers incethemethodsemployedbyDinsenbachertode velopequationsforaxialforces,verticalmom ent, spaperandtheystatetherefinementsmadetoSc hade smethods, (fromthesamepaper)whichincludetheequatio nsdevelopedarereproducedinAppendix3ofthi sreport.(Thereferencenum-bersinthequotat ionrefertothereferencesinthepaperwhichar ealsoincludedinAppendix3.) (1). (2).ThecomparisonshowedSchade ,Schade smethodrelateswaveheightonlytoshipdimens ions, ,thewaveamplitudesarerelatedtothecurrent designwaveheight-lengthrelationshipandto theloadsmeasuredontheASRcatamaranmodel. ,thecurrentdesignwaveheight-lengthrelati onshipusedforlongi-tudinalstrength,model andfull-scaleevaluationsofcurrentsurface -shiphullgirderdesignImds, Assumptions:(QuotationContinued) Forthisstudy,inamannersimilartothatofSch ade,theshipisideal-izedastworectangularr ectangularprisms(representingthehulIs)co nnectedbyabox(thecross-structure).]

8 ,beam,draft, (spanbetweenhulIs),width,depth,weightrcl earanceabovestilIwater,andverticallocati onofneutralaxisasdoestheactualcross-stru cture,Thefluiddensityusedforthecomputa-t ionofverticalforcesismodifiedheretocompe nsateforthedifferenceindisplacedfluidbet weentherectangularblocksandtheactualhull formsaswasdonebySchade;however, ,thedraftsarefoundfortheprismaticformswh ichproduceverticalaccelerationsof~ , * sservicelife(3). ,onlytheloadingconditionsshowninFigures1 and2willbeconsidered, :AxialForce:Theequationforaxialforceinbe amseasdoesnotaccountforthepos-sibleforce contributionduetothehorizontalaccelerati on,whichcanbesubstantial, (seeAppendix3,Figure1). (75),Appen-dix3, ~ ,:,Equation(79)Appendix3,developedformax imumtorque(whichoccursinobliqueseas)abou tthetwistcenterofthecross-structureisITO =SCbgBAL2/2~+ ,whilethesecondtermrepresentsthetorsiond uetoshearactingthroughtheship scen-terofgmvity, (foracatamaranwithweightlesscross-struct ure) , :hetestdata(Section4).

9 (4)entitled StructuralAnalysisofCatamarans asoneprtofashortcourseon ModernTechniquesofShipStructuralAnalysis andDesign formulaforcross-structureclearanceabovel oadwaterlineisC=3+ {~)butC< scross-structureislmwshapedanddesignedfo rlowcl* , (referredtoasRegion2)isquoteddirectlyfro mThomas lecturenotes(4). InRegion2, , Loadsfromslammingonthecross-structurebot tominRegion2canbedividedintotwokinds:(a) short-termhigh-impactpressuresactinglo-c allyinthelateraldirectionfor~nelsandonth eedgesoffloorsand(b)longerdurationforlow erpressuresusedforcross-structurebottomb entandoverallcross-structurebottomgrilIa gedesign. ! *p= ,Vistherelativemotionbetweenshipandfluid infeetpersecond,andthevalue64 ,sinceimpactpressuresareassumedtooccurwh entheshipdescendsontopofthewav~, ,thesepressuresareusualIyverylocalizedto thewater-structureinterfaceandwereas-sum edtocarryinsufficientmomentumtoaffectthe designoftheplating. *Chuang, , ExperimentsonFlat-BottomSlamming, JournalofShipResearch(March1966) ThefirstmentionedunpublishedNPLreportsho wedthatraisingthecross-structureonacatam aranmodelreducedthefreque~ ** (Beaufort6inonecaseandState7seainanother ),short-term,high-impactslammingpressure scanbeassumedtobebetween80and120psi,rega rdlessofthesizeoftheshiporheightofthecro ss-structure(withinreason).}

10 SlammingpressuresfromtheChuangequationfe llwithinthisrangeforallcatamaransofthese ries. Highimpactflat-bottomslammingpressureswe reappliedoversinglepanelsofbottomplating whichwerethendesignedasforboundariesofta nks,andtofloorsanddoublebottomlongitudin algirderstodesignagainstlocalcollapse. Followingtheinitialslamonthebottomplatin gofthecross-structure,thepressurecanbeas sumedtodropveryrapidlytothatgivenby1/2~V 2where?isthemassdensityofseawater, ,wherePistheistherelativeP= , ,Glaeserpre-paredanundergraduatethesisen titled ATheoreticalInvestigationIntotheMotionso faCalamaranandtheShearandBendingMomentso nitsCross-Structure (14).Theresponsesconsideredwereheave,rol 1, ,GlaesercalculatedtheresponsesfortheASRa ndcomparedthemwiththemodeltestresults(11 ).Figure1(takenfromthesummaryofthethesis )showsthecompari-son.**PritchettrC., ModelStudiesofASR-CatamaranImpactPressur esonBetweenHullStructure, NavalShipResearchandDevelopmentCenterT&E Report340-H-01(January1970).15 HEAVERE5 PohJ5~IllsIIIII1,\/I111,2,4,6,51,01, ~ ,O4 THEOL?