Sec. 64.3 



SHIP-DESIGN SPECIFICATIONS 



449 



certain warm, salt-water portions of the route, 

 the vessel is traversing the open sea and exposed 

 to fouling for only a fraction of the voyage time, 

 averaging probably not more than 0.6 of that time. 

 Furthermore, the relatively high speed at which 

 it is expected to travel prevents this menace from 

 becoming more than a normal factor in powering. 



The dock-to-dock schedule which the owner- 

 operator has laid out is divided into a canal-and- 

 river schedule and an open-sea schedule by apply- 

 ing the allowable navigational speed of 10 kt in 

 the ship canal in and out of Port Amalo and a 

 reasonably safe speed through the river in and 

 out of Port Correo. After docking and maneuver- 

 ing time at all ports is taken into account, the 

 buoy-to-buoy schedule comes out of the remaining 

 time and distance by simple arithmetic. For this 

 sea schedule the average speed made good in 

 open water, at either full load or any intermediate 

 displacement and corresponding trim, in fair 

 weather or foul, with smooth or rough bottom, 

 works out as a minimum of 18.7 kt. 



This is a week-in, week-out performance speed 

 and not a design figure. The ship must be capable 

 of an augmented sea speed to guarantee making 

 the average sustained speed of 18.7 kt under the 

 handicaps of wind, weather, waves, currents, 

 and fouling. The manner of accomplishing this 

 is explained under Design and Performance 

 Allowances in Sec. 65.3 and under Powering 

 Allowances in Sec. 69.9. Suffice it to say here that 

 the analysis thus made indicates the necessity 

 for the ship to be capable, in smooth water, 

 with clean bottom, at full designed load and in 

 zero natural wind, of making at least 20.5 kt. 

 Other considerations of easy steaming, freedom 

 from wear and tear, long intervals between 

 major machinery overhauls, and general depend- 

 ability of both materiel and personnel, discussed 

 in Sec. 69.9, require that the 20.5-kt speed be 

 accomplished by the development of only 95 per 

 cent of the maximum designed power. 



Summarizing this analysis and working in a few 

 related supplementary features produces the 

 speed and wavegoing requirements of Table 64. d. 

 Restrictions against pounding, slamming, and 

 lurching, against being pooped in a following sea, 

 and against carrying away gear on deck are not 

 listed separately because they are implicit in 

 items (3) and (4) of the mission, set forth in 

 Table 64.a. 



Before going further into the speed and pro- 

 pulsion specifications, the maneuvering require- 



TABLE 64.d — Speed and Wavegoing 



(20) The average or sustained sea speed made good in 

 each deep-water, open-sea portion of the voyage, 

 in any or all service displacements and under cor- 

 responding trim conditions, in any weather, and 

 with any reasonable amount of bottom roughening 

 and fouling, shall be at least 18.7 kt 



(21) The augmented sea speed, to achieve the sustained 

 speed, is set tentatively at 20.5 kt. This is to be 

 made in smooth, deep water, with clean bottom, in 

 zero natural wind, and at any and all service dis- 

 placement and trim conditions. 



(22) Whatever the augmented sea speed, it shall be 

 attained by the use of not more than 95 per cent of 

 the maximum designed power of the propelling 

 machinery 



(23) In general, the ship and machinery shall operate at 

 maximum efficiency under conditions (21) and (22) 



(24) The ship may have to slow temporarily in heavy 

 weather to 65 per cent of its average sea speed of 

 18.7 kt; this is 12.16 kt. If so, the schedule must be 

 met by a corresponding increase in the speed in 

 good weather. The estimated reduction in speed for 

 constant thrust equivalent to a smooth-water speed 

 of 20.5 kt shall not exceed 45 per cent when running 

 into a head sea, at an angle of encounter of 180 deg, 

 through regular waves having lengths Ljp of from 

 0,8 to 1.5 the ship length L, and heights h^ not 

 exceeding 0.55^/ Lw- (The speed reduction from 20.5 

 kt to 12.16 kt is 40.7 per cent). Water ballast, 

 preferably fresh water, may be admitted to groups of 

 empty liquid cargo tanks as desired to establish 

 satisfactory propeller submersion and to provide 

 added ship mass on the outward voyage from Port 

 Amalo, when the liquid bulk cargo is not on board. 



(25) The ship shall be as free of resonant pitching in the 

 waves to be encountered as may be compatible with 

 other requirements 



(26) A reasonable expenditure of weight or power, or 

 both, to secure effective roll-quenching is acceptable 

 to the owner. Effective quenching is defined as 

 diminishing the roll angle to 0.25 (one-quarter) of its 

 natural value. 



ments are considered because they may bear 

 some relation to the number and position of 

 propellers to be installed. An analysis of maneuver- 

 ing, in turn, calls for a statement of the restricted- 

 water characteristics of various parts of the 

 vessel's route, somewhat similar to that of the 

 meteorologic and oceanographic conditions affect- 

 ing wavegoing. The principal features are set 

 down in items (27) through (29) of Table 64.e. 

 The canal bend at Mile 20 is diagrammed in 

 Fig. 64. A, which contains also the estimated 

 tracks of large vessels proceeding in both direc- 

 tions, with their limiting offset positions in the 

 canal. The essentials of the maneuvering situation 

 at Port Bacine are copied from the chart in Fig. 

 64.B, with the estimated ship tracks and positions 



