448 



HYDRODYNAMICS IN SHIP DESIGN 



Sec. 64.3 



size and displacement volume. The ship hull 

 must have enough bulk volume to contain all 

 that is to be put inside it, both below and above 

 water. It must have enough displacement volume 

 to float itself when carrying a high-weight- 

 density cargo which does not fill its holds. List 

 these volumes and weights as a preliminary to 

 estimating and determining the total weight, bulk 

 volume, and principal dimensions of the ship, 

 but do not attempt to fix the latter features at 

 this stage. 



Whatever the custom and procedure may be 

 elsewhere for determining the overall size of the 

 ship, it is assumed here, for the sake of working 

 up a well-proportioned design, that there is no 

 major limitation on size and dimensions except for: 



(a) The general requirement (5) of Table 64.a for 

 the greatest performance from the least ship 



(b) A specific draft limitation for passage of a 

 canal and a river during the voyage. 



TABLE 64.b — Considerations of Size and 

 Displacement Volume 



The ship shall be able to: 



(7) Carry a liquid-bulk cargo of 4,000 t (of 2,240 lb) from 

 Port Correo to Port Amalo on each trip, for which 

 liquid the weight density will not exceed 42 ft^ per 

 ton of 2,240 lb [Wormald, J., "The Carriage of 

 Edible Oil and Similar Cargoes," IME, Apr 1956, 

 Vol. LXVIII, pp. 65-91] 



(8) Carry a total weight of package cargo not exceeding 

 3,000 t back and forth between all ports, requiring 

 a net or usable storage space not less than 300,000 ft' 



(9) Load and unload package cargo at Port Bacine, 

 both coming and going, without disturbing any 

 through package cargo 



(10) Carry sufficient fuel to permit bunkering at Port 

 Correo and making the round trip to Port Amalo and 

 return, on the basis of the rigid all-year schedule 

 specified in the foregoing, plus a 15 per cent reserve- 

 fuel capacity. The weight density of the fuel will not 

 exceed 42 ft' per ton. 



(11) Carry sufficient fresh water and consumable stores, 

 stocking up at Port Amalo and replenishing upon 

 return, to permit making the round trip to and from 

 Port Correo 



(12) Devote a volume of 400,000 ft' of enclosed space 

 exclusively to passenger service 



(13) Make a safe and expeditious passage, under its own 

 power, of the 25-mi ship canal leading to Port Amalo, 

 which has a minimum depth of 28 ft 



(14) Negotiate without assistance the 204-mi passage of 

 the fresh-water river from Port Correo to the sea, on 

 the basis of a minimum depth of 30 ft in the navigable 

 area 



(15) The size and weight of the ship shall be a minimum 

 consistent with these and subsequent performance 

 requirements. 



The outcome of this procedure, for the ship 

 selected as the example, is contained in Table 64. b. 

 A speed requirement is not yet in the picture. 

 Indeed, before beginning consideration of it 

 there is prepared a summary of the meteorologic 

 and oceanographic conditions which the vessel is 

 to encounter. Table 64. c contains the summary 

 for this design problem. If these conditions vary 

 during the operating season, as is usually the 

 case, they are carefully analyzed and evaluated. 



TABLE 64. c — Meteorologic and Oceanographic 

 Conditions 



(16) Full account shall be taken, as important factors in 

 the design, of the meteorologic and oceanographic 

 conditions in the regions in which the ship is to 

 operate. The average latitude over the whole voyage 

 is 20 deg. Surface winds, along the fringes of the 

 hurricane belt between Port Amalo and Port Bacine, 

 may be expected to blow from any direction at 

 velocities up to 90 kt. These are accompanied by 

 ocean waves corresponding to a fetch of at least 500 mi 



(17) Tidal currents in the long ship canal leading to 

 Port Amalo may reach 0.5 kt. In the river between 

 the sea and Port Correo the combined tidal and river 

 current may reach 2.75 kt, flowing downstream. 



(18) Water temperatures in the fresh-water river at and 

 below Port Correo range from 75 to 80 deg F; those 

 in Ports Amalo and Bacine range from 60 to 75 deg F. 

 It shall be possible to deliver the maximum designed 

 or rated power of the propelling machinery with a 

 sea-water temperature of 75 deg F. Water tempera- 

 tures in the open sea average about 68 deg F. 



(19) Fouling is a factor to be reckoned with at all seasons 

 of the year while the vessel is at sea. Fouling may 

 stop temporarily while the vessel is in the ship canal 

 leading to Port Amalo and in the fresh-water river 

 leading to Port Correo but the roughnesses already 

 accumulated will not disappear. 



Hurricanes of major proportions may be ex- 

 pected to occur along part of the route during 

 only some three months of the year. However, 

 unexpected and troublesome storms, with large 

 steep waves, often are encountered for a month 

 and a half or two months before and after the 

 hurricane season, overlapping the seasons of heavy 

 passenger travel. Full account of these adverse 

 conditions therefore is taken when laying out 

 the design. With the rather careful modern 

 plotting and hour-by-hour reporting of storm 

 centers to be expected in the worst areas, it may 

 be possible for the ship, with an ample reserve 

 of speed, to save time by running around the 

 storms rather than remaining on course and 

 slowing down to go through them. 



Although heavy marine fouling is the rule in 



