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

-106-such as iron ore, on two of the three legs, the spread between the RFR of’the steel and aluminum ships would be reduced.In an effort to evaluate these factors, an optimistic aluminum shipmodel has been established incorporating the following changes:(a)(b)(c)(d)(e)The 2S per cent labor differential has been eliminated.One-half of the 43s ton fatigue allowance has been eliminated.The 100 ton abrasion.allowance on the tank top and wing bulkheadshas been eliminated.Fire protection for the deckhouse has been modified per ItemS previously discussed.A three leg voyage with weight-sensitive cargoes carried on.two legs over distamces of 4000, 84OO and 12,000 miles havebeen assumed, with ship life of 20, 25 and 30 years, to beconsistent with previous studies (Table 28).The reduction in first cost of the ship is $1,600,000 for singleship procurement, and the available deadwight has been increased by 360tons ● Thus the 7-1/2 per cent increase in available deadweight of the baselineship increases to about 8-1/2 per cent.The three-leg voyages were considered with the following assumptions:oRound voyage distances, ship life and number of shipspurchased are identical to the figures of Table 28.0 Average Annual Costs for all items which do not vary withacquisition cost are identical to the two-leg voyage.This may not be entirely accurate with regard to such itemsas fuel costs but it is felt that this discrepancy will notmaterially affect the final results.oSince cargo is carried on two of three legs instead of one oftwo legs, annual cargo carried will increase by 33 per centover the values listed in Table’28.0 An additional increase of 1 per cent for cargo carried overthe two leg voyage as listed in Table 28 was assigned to thealuminum vessel because of increased cargo deadweight due tothe reductions in lightship.ooSalvage value of the aluminum vessel was reduced directly inproportion to changes in material weight of the vessel asoriginally conceived+Owners Investment costs, i.e., non-depreciable costs in.curred during construction, were assumed independent ofacquisition costs.As indicated in Table 29 and Figure 23, the steel bulk carrier haslower RFR’s than,the aluminum ship for equal life spans, even for thishighly optimistic case.