464 HYDROnYNAMICS IN SHIP DESIGN Src. ^^.'? 



(c) Hull and fittings 6,400 t types of recent American ships, are given in 



(d) Propelling machinery 800 t convenient form by Nevitt [ASNE, May 1950, 



(e) Fuel, including reserve 2,200 t pp. 303-324]. However, in common with many 



(f) Consumable supplies and stores in other graphic aids of this kind, there is nothing in 



heaviest condition 400 t the reference to indicate the basis on which the 



(g) Tentative margin, about 3 per cent original designer selected a certain ratio or param- 



of the total 500 t eter for a ship represented by a given spot on a 



diagram. Furthermore, one does not know 



Estimated weight displacement, (a) whether the ship represented by that spot was 



througii (g) 17,300 t easily driven or otherwise. This latter situation is 



In kips of 1,000 lb, 38,752 remedied partly by taking data from the SNAME 



Resistance Data sheets. These give in most cases 



The corresponding displacement volume, at a the predicted effective power for a ship of standard 



round figure of 35 ft' per ton of salt water, is length with respect to that for a Taylor Standard 



605,500 ft . Series ship of the same length. 



Another way of arriving at the estimated 66.5 First Approximation to Principal Dimen- 



weight displacement is to base the hull, machinery, sions ; The Waterline Length and Fatness Ratio, 



and other fixed weights on a percentage of the The next logical step is to estimate roughly the 



total. The useful load is, including the fuel: length of the ship. As pointed out in Sec. 24.2, 



(1) Liquid bulk cargo 4,000 t this length for the ABC ship is on the waterline, at 



(9) Package cargo 3 000 t ^ ^"^^^^ correspondmg to the designed maximum 



(3) Fuel, including reserve' '.'.'.'.'.'. 2^200 t s^^'^i'^'' ^""^^ ^t which a speed of 20.5 kt is to be 



(4) Total amount of fresh water, supplies, achieved in smooth water. A tentative length 



and consumable stores for which "^a^ be taken from plots of empirical data such 



storage is to be provided on board . 700 t ^^ ^^^^^ "^ Levitt [ASNE, May 1950, Figs. 7, 8, 



9, pp. 308-309], or it may be read by inspection 



Total 9 900 t ^^^^^ the analysis summaries of the SNAME RD 

 sheets for combination passenger and cargo ships 



A combination passenger and cargo vessel of of about 17,500 tons displacement, and designed 



this type should be able to carry 0.55 of its weight speeds of the order of 18.7 to 20.5 kt. The former 



as useful load, leaving 0.45 of the displacement as plots give an Lpp of about 480 to 500 ft for normal 



the ship weight. Using the first displacement ships and 500 to 520 ft for fine ships. This cor- 



estimate of 17,300 t and this ratio of 0.55, the responds to an Ldwl range of about 500 to 535 ft. 



useful load is 9,515 t, only slightly smaller than The latter tabulation gives a somewhat less 



the 9,900 t fisted in the paragraph preceding, definite value for L^wl of the order of 500 ft. 



Actually, of the latter amount, only 9,600 t is on A first guess at the minimum length is 500 ft. 



board in the designed maximum service-load For this length the Taylor quotient T, = V/ V L 



condition, as when loaded at Port Correo. This is 20.5/ VSOO = 0.917. The Froude number F„ 



is because 300 t of item (4) preceding is consumed is T, (0.2978) = 0.273, and the displacement- 



on the way from Port Amalo. length quotient A/(0.010L)' = 17,300/(5)' = 



The ship- weight portion of the total, 45 per 138.4. The 0-diml fatness ratio V/(0.10L)^ is 



cent, is 7,785 t, which is somewhat larger than 605,500/(50)' = 4.84. 



the sum of 6,400 t for hull weight and 800 t for The question now arises, How do these param- 



machinery, items (c) and (d) of the previous eters fit together to insure a ship easily driven? 



tabulation. A small-scale graph of the ratio of Is the length too small for the displacement and 



useful load (actually deadweight) to total design the required speed? Is the ship too fat for its 



displacement, for large passenger vessels and speed? Considering hydrodynamics only, ship 



Atlantic hners, is plotted by C. R. Nevitt on a length is a matter of providing the easy longi- 



basis of speed-length quotient V/ a/L or Taylor tudinal curvature necessary to permit an under- 



quotient T, , within the range of 0.70 to 1.05 water body of the requisite volume to be driven 



[SNAME, 1945, Fig. 1, p. 316]. More recent easily and efficiently at the specified speed. In 



plots for selecting this and many other ratios and selecting the length, however, several other 



parameters, based upon data from certain general hydrodynamic factors enter: 



