design considerations for aluminum hull structures - Ship Structure ...

-1o5-SENSITIVITY STUDIESThe basic economic studies recently completed were based upon afixed set of criteria, both in terms of ship cost and operational considera%iorm.It is of in%erest to investigate the possible effects onlife cycle economics of varying these factors, to determine which hasthe greatest effect on p~ofitability and thus deserves greatest attentionin future studies of this nature.1. Direct Labor Cost - Aluminum Hull - If it is assumed that the25 per cent differential in labor between aluminum and steel can beeliminated, the potential reduction in direct labor, overhead and profitwould be approximately $580,000 for single ship procurement, with correspondinglylower reductions for larger procurements. This is about 3 pe~cent of procurement cost.2* Profit - Aluminum Hull - If it is assumed that the shipbuilderwill accept the same profit for building an aluminum or steel ship, thepotential savings is about $400,000. However, this is unlikely, since thebuilder would desire to show at least an identical return on his investmentand might even prefer a higher return on the aluminum hull due to thegreater risks involved.3. Hull Girder Fatigue Allowance - If the 43S ton increase in hullgirder weight for fatigue could be completely eliminated, the first costof the aluminum bulk carrier would be reduced by about $1,160,000 or 6 psa’cent and the available deadweight would be increased accordingly. However,there is presently no technical justification for such a reduction, thoughfurther study might lead to the conclusion that a portion of this allowancecould be eliminated.4* Tank Top Abrasion/ImpactAllowance - If bhe 0.80 inch allowancefor impact and abrasion on the aluminum shipls tank top and wing bulkheadscould be reduced to 0.2~ inches (the American Bureau of Shipping required0.20 inches for steel times the factor for relative yield and ultimatestrength differences), the potential weight savings would be about 100 tonsor a cost savings of $270,000, with a corresponding increase in deadweightcapaci%y.5+ Fire Protection - The additional cost associated with fire protectionof the aluminum bulk carrier, including insulation and sheathing isabout $260,000 greater than that of the steel ship, based upon full compliancewith the intent of the present U.S. Coast Guard fire protection rules. About$160,000 of this is associated with deckhouse protection. If the requirementsfor deckhouse protection were waived except in stair towers, uptakes andhigher fire risk areas (the galley for example), it would be possible toreduce the shipls first cost by about $1~0,000 and its weight by about 40tons. Although this involves greater risk to the crew, it would not havea major effect on hull girder strength,since a fire in the deckhousecould be isolated from the main hull by proper deck covering. Such aproposal would, of course, require intensive investigation and approvalby the U. S. Coast Guard.6. Voyages - The voyages investigated for this study are consideredgeneralmesentative of the spectrum of tramp operations duringthe next 20 years, and result in a number of ballast or volume-sensitivelegs which do not afford any advantage to the aluminum bulk carrier. Ifsuch a ship were to be engaged in a trade with weight-sensitive cargoes,