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

-87-SEI13CTIONOF PRINCIPAL DIMENSIONSThe principal dimensions of the steel bulk carrier will be identical to‘choseof the M.V. CWALIENGER, as delineated in Table 1. The aluminum bulkcarrier is assumed to be identical in full load displacement, with the reductionin light ship weight used to increase the cargo deadweight, and thusthe earning capacity. The anticipated increase in available cargo deadweightis about !?,700tons or 7-1/2 per cent, which means that the existing cargohold dimensions would be satisfactory for all but the most volume-criticalcargo~s such as grain. For a new design, the hold volume could be increasedaccordingly. However, for this study, the volume of the cargo holds for thesteel and aluminum ships will be kept identical to permit direct comparison.All hull dimensions ad form coefficients of the two ships are to beidentical~ so that speed-power relationships at full load displacement aresimilar. This means that the power plants of the two ships will be identical,thereby eliminating costs associated with the machinery system as variables.It is recognized that this approach, although satisfactory for a feasibilitystudy, will not necessarily result in an optimum aluminum hull. For example,the reduction in hull weight without a corz-espondingreduction in the machineryweights will result in greater trim by the stern in some conditions. It mightalso be desirable to increase the hull and double bottom depth to increasestiffness. However, these are the type of refinements which can easily beincorporated in the design if desired, but which should be excluded from thisfeasibility study if a direct basis is to be maintained for comparing the twodesigns.Another feature of the M.V. CHALLENGER which bears consideration is theselection of propulsive power. The ship, as built, is powered by a 9,600 SHPdiesel engine, which is questionable for U. S. Flag operation. A brief investigationwas made of the feasibility of installing a steam plant within thepresent hull. This study indicated that the following changes would be requiredto facilitate installation of a steam plant:(a)(b)(c)Increase the height and/or length of the machinery box.Modify the weight of the propulsive system.Increase the fuel capacity to maintain the present ramge, dueto the higher specific fuel consumption of the steam system.Thethemagnitude of the above changes would necessitate a complete redesign ofship, even for this prelimina~ feasibility study.Since the machinery systems of both the steel and aluminum ships are tobe identical, and thus do not directly affect the relative economic tradeoffsbetween the two designs, it appears p~eferable to retain diesel propulsionfor this study in order to preserve the integrity of the existing design.DESIGN OF MIDSHIP SECTION‘Themidship section of a steel bulk carrier equivalent to the M.V.CHALLENGER, designed to suit 1969 ABS Rules, is shown in Figure Is. Thissection differs slightly from that of the M.V. C~LLENG~ shown in Figure2, to reflect upgradtig of scantlings to suit the latest Rules, and eliminationof the additional bottom plate thiclmess requested by the owner asan abrasion allowance.