Sec. 66.4 



STEPS IN PRELIMINARY DESIGN 



463 



intended to be burned except in an emergency, 

 constitutes the reserve fuel supply. Whether it 

 equals or exceeds the 15 per cent required by 

 item (10) of Table 64. b remains to be seen as 

 the design progresses. If the ship is slowed by 

 heavy weather it is nevertheless assumed that 

 the fuel-consumption rate remains the same as 

 for maximum designed power and for a speed 

 slightly in excess of 20.5 kt in good weather. 

 The fuel consumption when traveling in the 

 shallow and restricted portions of the route is 

 estimated only roughly for the present. 



66.3 Probable Variable-Weight Conditions. 

 Although the variable weights are not, strictly 

 speaking, a part of the hydrodynamic-design 

 picture, they do affect it in that they govern 

 the displacement and trim and hence the volume 

 and shape of the underwater hull in the several 

 operating conditions. They also, with the respec- 

 tive specific gravities of the water, vitally affect 

 the bed clearances that will obtain in the shallow 

 and restricted portions of the route. In Table 66. d 

 there are set down seven conditions, out of 

 perhaps a dozen or more to be expected in the 

 course of a routine voyage, as an indication of the 

 range of displacement that might be encountered. 

 The amount of fuel to be carried is still a rough 

 guess, but the variations in total displacement 

 are far greater than any possible variation in 

 the fuel capacity. 



It is to be noted from Tables 64. b and 66.d 

 that since the bunkering for the whole voyage is 

 done at Port Correo and the replenishment of all 

 consumable stores at the other end of the line, 

 the full load for which storage space must be 

 provided is never on board at any one time. It is 

 estimated that of the 700 1 of fresh water, supplies, 

 stores, and other consumables which can be 

 carried, only 400 t is left on board at Port Correo, 

 when the full amounts of fuel, liquid cargo, and 

 package cargo are assumed to be loaded. As 

 indicated in the first line of Table 66.d, this 

 represents the maximum service load. 



66.4 First Weight Estimate. The first step 

 in the preliminary design is to determine the 

 approximate weight of the ship with its cargo, 

 the displacement volume required to support this 

 weight, and the approximate linear dimensions. 

 The following items of the weight estimate, all in 

 tons of 2,240 lb, are known from the requirements 

 of Table 64.b: 



(a) Liquid bulk cargo 4,000 t 



(b) Package cargo 3,000 t 



Guesses of other major weight items are based 

 on the background experience of the ship designer 

 and such reference data as he may have. These 

 items are deliberately set down here without 

 reference to any handbook or other information, to 

 make the example as general as possible. They are: 



TABLE 66.d — First Statement of Variable- Weight Conditions, ABC Ship 

 All weights are in long tons of 2,240 lb or 2.24 kips of 1,000 lb. 



*Somewhat less than half of the 700 t loaded at Port Amalo has been consumed 



