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

-114-2k* Installation of Systems and Equipment. Selection of materialsfor propeller, shafting, rudder, piping eysbems, sea valves, etc. whichare compatible with aluminum construction is feasible, though isolation andprotection with anodes or waster pieces is required in many cases.25. The faying surfaces between steel equipment and aluminum foundationsmust be properly gasketed. The use of cast epoxy at the interfaceor butyl rubber coating is recommended. Access to inspect this interface isvery important.26. An impressed current cathodic protection system is recommendedfor hull corrosion control.27. operational Characteristics OT an Aluminum Budk Carrier - l%intenancecosts for the hull of an aluminum bulk carrier will be somewhat lowerthan those of an equivalent steel vessel, since the topsfdes require nopaint. However, drydocking cycles will be essentially similar to the steelvessel for renewal of bottom paint and maintenance of equipment.28. Repairs to the aluminum hull will be more expensive than for asteel hull due to higher material cost and lack of trained welders in manya~eas of the world,29. Special surveys are recommended of the hull structure of a largealuminum bulk carrier to check structural connections, corrosion, welds, etc.30• Comparative Ship Desire and Evaluation - The principal dimensionsof the aluminum bulk carrier selected for this study are essentially similarto the baseline steel ship, although a deeper double bottom and g~eaterhull girder depth might be desirable for an independent design to increasestiffness.31. ,Theweight per foot amidsh~ps for the S083 aluminum alloy bulkcarrier will be about .62 times that of the mild steel ship, while thestiffness will be about 0.66 times that of the steel. The use of fatiguestrength rather than static strength in designing the hull girder addsabout 435 tons or Is per cent to the hull structural weight. For atypical bulkhead, the weight reduchion facbor is O.~~.32. The total weight of hull structure was reduced from ~920 to 33?slong tons, a savings of h3 per cent. The corresponding reduction inmachinery and outfit weight was 4 and IL per cent respectively.33. Greater ballast capacity is required for an aluminum bulk carrierto provide suitable propeller and bow immersion in the ballast condition.The stability of the ahunin~ and steel designs are essentially identical.34. Cost Studies. An.aluminum bulk carrier similar to the MV CHALLENGERproduces a higher required freight rate (RFR) than an equivalent steel ship,regardless of the level of procurement, voyage type or lengthJ potentialhull life or the higher salvage value of an aluminum ship. Thus thegreater earning capability of the aluminum hull is not sufficient to offsetits higher capital cost.35• The aluminum shipls RFR is lowest for high-density cargoes wherethe full weight savings can be considered (i.e. not volume limited). Thetransport capability of the aluminum ship is about 7 per cent greater thanthat of the steel ship.