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1、LessonOneTheNavalArchitectAnavalarchitectaskedtodesignashipmayreceivehisinstructionsinaformrangingfromsuchsimplerequirementsas“anoiltankertocarry100000tonsdeadweightat15knots”toafullydetailedspecificationofpreciselyplannedrequirements.Heisusuallyrequiredtoprepareadesignforavesselthatmustcarryacert
2、ainweightofcargo(ornumberofpassengers)ataspecifiedspeedwithparticularreferencetotraderequirement;high-densitycargoes,suchasmachinery,requirelittleholdcapacity,whilethereverseistrueforlow-densitycargoes,suchasgrain.Deadweightisdefinedasweightofcargoplusfuelandconsumablestores,andlightweightasthewei
3、ghtofthehull,includingmachineryandequipment.Thedesignermustchoosedimensionssuchthatthedisplacementofthevesselisequaltothesumofthedeadweightandthelightweighttonnages.Thefinenessofthehullmustbeappropriatetothespeed.Thedraft------whichisgovernedbyfreeboardrules------enablesthedepthtobedeterminedtoafi
4、rstapproximation.Afterselectingtentativevaluesoflength,breadth,depth,draft,anddisplacement,thedesignermustachieveaweightbalance.Hemustalsoselectamomentbalancebecausecentresofgravityinbothlongitudinalandverticaldirectionsmustprovidesatisfactorytrimandstability.Additionally,hemustestimatetheshafthor
5、sepowerrequiredforthespecifiedspeed;thisdeterminestheweightofmachinery.Thestrengthofthehullmustbeadequatefortheserviceintended,detailedscantlings(framedimensionsandplatethicknesses)canbeobtainedfromtherulesoftheclassificationsociety.Thesescantingsdeterminetherequisiteweightofhullsteel.Thevesselsho
6、uldpossesssatisfactorysteeringcharacteristics,freedomfromtroublesomevibration,andshouldcomplywiththemanyvariedrequirementsofinternationalregulations.Possessinganattractiveappearance,theshipshouldhavetheminimumnetregistertonnage,thefactoronwhichharbourandotherduesarebased.(Thegrosstonnagerepresents
7、thevolumeofallclosed-inspacesabovetheinnerbottom.Thenettonnageisthegrosstonnageminuscertaindeductiblespacesthatdonotproducerevenue.Nettonnagecanthereforeberegardedasameasureoftheearningcapacityoftheship,henceitsu
