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

Fromavailable deadweight for weight critical cargoes. It is assumedthat the use of inorganic zincs or equal in conjunction with areasonable maintenance program will prevent excessive corrosionof the topside plating.(3) Procwement costs for machinery and outfit were assumed identiaalfor 20, 2S and 30 year lives, since they do not directly affectthe qualitative results of the study. In reality however, i% isobvious, that the cost of equipment with a 30 year life will behigher than for a 20 year life, in most cases.The first voyage of I,!I,300miles consisted of the following legs:%0—DistanceSeattle Yokohama 4,280 WheatYokohama Gladstone, Australia 3,600 BallastGladstone Tacoma 6,400 AluminaTacoma Seattle 20 BallastThe second voyage of 2S,310 miles included these legs:From To Distance— -New Orleans Bohbay 11,890 WheatBombay Port Buchanan, Liberia 7,~20 BallastPort Buchanan Baltimore 4,2oo Iron OreBaltimore New Orleans 1,700 BallastAn additional eighteen cases were computed on the basis of threedifferent two-leg voyages of 4,000, 8,4oo and 12,000 miles round trip.These cases represent better opportunities than do the four-leg voyagesfor the aluminum bulk carrier to benefit from its g~eater deadweightcapacity over that of the steel ship. These voyages contained one legwith a dense cargo, iron ore, as the cargo while the other leg was inballast. Computations were made for single ship procurement with shiplife varied at 20, 25 and 30 years. Results of the two-leg voyages appearon Table 28.Many of the operating and maintenancecost assumptions were basedupon data which appears in the working papers on the dry bulk carrierevaluation model, Reference (69).RESULTS-1o1-Four graphs were plotted to illustrate the results of the computations.Figure 3.9compares RFR versus round voyage distance for the steel andaluminum ships on both the two-leg and four-leg voyages. This figureclearly shows that the two-leg voyages provide the better competitiveopportuni~ for the aluminum ship because on these voyages with dense cargo,the full weight savings advantage of the aluminum ship is reflected. However,even with a 30-year life, the aluminum ship requires a higher RFRthan the steel ship for the voyages examined. Fi~re 20 is a plot of RFRversus ship investment cost for the 14,300 mile, four-leg voyage. It ispossible to estimate the reduced price which would be required for thealuminum ship, to provide an.RFR equal to the steel ship, by projecting