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

-1o9-7. REcoMMENDEDAREAS FoR FURTHER STUDY. .One of the results of a limited feasibility study such as this, isthat numerous quesbions are raised wh~ch can not be satisfactorilyanswered within the time or cost allocated to the study. The aluminumbulk carrier study is no exception, and in the following pa~agraphs, themajor areas requiring further sbudy are delineated. These areas arelisted approximately in omier of priority, based upon their relativeimportance in establishing feasibility of using aluminum for the hullstructure of large ships.CONSTRUCTION COSTSThe cost of fabricati~ large aluminw ship structures must be morefully defined to permit more accurate construction cost estimates andtrade-offs of alternative construction techniques. At present, it isnecessary to use approximate over-all manhours-per-poundvalues to estimatelabor costs and associated overhead, which do not permit the type of relativelysophisticated trade-offs required to optimize structural design. Forexample, it is difficult to choose between various potential methods ofp~oviding ~equired deck area, such as thick plates, thinner plates withdoublers OF double wall cellular construction. Several qualified shipyardsshould be authorized to evaluate the construction costs of large aluminumhulls in greater detail.MAINTENANCE COSTSEkduced hull maintenance costs are a key selling point of aluminum,and data is required to more accurately evaluate the life cycle hull maintenancecost of an aluminum,hull for comparison to the equivalent steelhtil. This is particularly important as the ships get older, since thecosts of steel hull repairs begin to increase rapidly as plate replacementbecomes necessary. The best potential source of long-term hull maintenancedata on large aluminum hulls would be Navy records on the hull maintenanceof the PGM gunboat. ‘Thisdata should be closely monitored and periodicallyevaluated by the Ship Structures Committee and applicable Navy activities.WELDINGThe technology of welding thick.aluminum plates to form subassembliesunder shipyard conditions as well as the erection of subassemblies requiresconsiderable investigation. Areas of particular concern are weld sequence,heat input, edge preparation, speed of welding, required level of cleanlinessand enviro~ent control and quality control required to affect soundwelds with minimum cracking, porosity, inclusions, residual stresses anddistortion. An area of major concern is the possible need to accomplishwelding in a protected environment to maintain adequate control on moistureand cleanliness.FIRE RESISTANCEThe analysis of the fire problem which was conducted for this study wasof necessity somewhat limited, and should be extended to include the resultsof the SNAME fire ‘testprogram. Additional economic trade-offs are requiredto optimize the protection of alumin~ structures as well as means ofdetecting, extinguishing and preventing fires. Proposed areas to be investigatedin further detail are as follows: