Sec. 66.9 



STEPS IN PRELIMINARY DESIGN 



471 



portions for a ship of the speed and service 

 required, although the beam is still large. 



Supplementing the discussion in Sec. 24.11, 

 Fig. 66. E gives a range of absolute beams on a 

 basis of absolute lengths, based on data from 

 many successful ships, for which a great number 

 of the spots are shown. The meanline indicated is 

 rather an average location for most of the ship 

 values than one drawn through the center of the 

 lane marked by the upper and lower ranges of 

 absolute beam on absolute length. Also indicated 

 is a curve of 0-diml L/B ratios corresponding to 

 the meanline. 



Some modern craft built for speed with manual 

 propulsion only, among them canoes, sculls, and 

 racing shells, retain the high L/B ratios charac- 

 teristic of dugout and American Indian canoes 

 for many centuries past. However, there has been 

 an increasing demand through the years for 

 utility, for inherent stability not always possessed 

 by the canoe with a man (or men) standing up 

 in it, for still more utility with top hamper, and 

 finally for greater all-around safety. This has 

 broadened the beam of boats and small ships 

 gradually, without too much regard for the effect 

 of the small L/B ratio on propulsion. If meta- 

 centric stability, maneuvering, and other features 

 are more important than propulsion, the design 

 has to favor them. 



For the ABC design the beams given in the 

 preceding paragraphs are slightly greater than 

 those shown by the meanline but they are well 

 within the lane. 



The block coefficient for the 525-ft vessel works 

 out as 



Cs = 



605,500 



= 0.595-1- 



L{Bx)Hx 525(74.52)26 

 This checks, as it should, with 



Cb = Cp{Cx) = 0.62(0.96) = 0.595-F 



For the three waterline lengths of 500, 515, 

 and 525 ft, and for a constant Cp of 0.62, the 

 proportions and dimensions already worked out 

 and some of those remaining to be derived are 

 indicated for convenience in Table 66. e, in Sec. 

 66.11. 



66.8 First Estimate of Hull Volume. It is 

 advisable at this point to make a rough volu- 

 metric check of the vessel to insure that everything 

 can be accommodated within the hull, above as 

 well as below water. It is now necessary to include 

 the full weight and volume of consumables and 



other items to be carried during any part of the 

 voyage. Using the data from Table 64. b and the 

 same subdivision as in the first weight estimate 

 of Sec. 66,4: 



(a) Liquid bulk cargo, 4,000 t at 



42 ft' per t 168,000 ft' 



(b) Package cargo, 3,000 t at 100 



ft' per t 300,000 ft' 



(c) Hull structure, on a basis of 4.5 

 ft' per t for 6,400 t of hull steel, 

 fittings, and other construction 

 materials, -plus 4 times that vol- 

 ume for the waste space around 



it 144,000 ft' 



(d) Estimate for propelling and 



other machinery 300,000 ft' 



(This is very large compared to 

 the figures given by G. G. Sharp 

 [SNAME, 1947, p. 462] but in 

 view of the unorthodox features 

 being considered for an alterna- 

 tive stern, with the propelling 

 machinery aft, it is not reduced 

 at this stage) 



(e) Fuel, 2,200 t at 42 ft' per t . . 92,400 ft' 



(f) Fresh water, lubricating oil, sup- 

 plies, and other consumable 



stores, 700 t at 100 ft' per t . 70,000 ft' 



(g) Accommodations for officers and 



crew, estimated 100,000 ft' 



(h) Passenger quarters and service . 400,000 ft' 

 (i) Non-usable space 100,000 ft' 



Total volume 1,674,400 ft' 



The foregoing does not include an allowance 

 for keeping hatchways clear, to facilitate access 

 to the cargo, nor for the volume of expansion 

 trunks over the liquid-cargo tanks. 



The volume listed is about 2.77 times the 

 tentative underwater displacement volume of 

 605,500 ft' but it includes practically all deck 

 erections. For a combined passenger and freight 

 vessel, it appears somewhat large but perhaps 

 not too large at this stage of the design. 



66.Q First Approximation to Shaft Power. 

 Before making a second weight estimate it is 

 necessary to approximate the propelling power, 

 so as to determine more accurately the machinery 

 weights and the fuel capacity. 



The first rough estimate of shaft power Ps 

 is derived from the assembled data on merit 

 factors in Sees. 34.10 and 60.13. The first of these. 



