Sec. 60 J 



SHIP-POWERING DATA 



357 



representing a reduction — sA of 14.8 per cent 

 from the designed value, the corresponding rela- 

 tionships are, from Eq. (60.i), 



Pe for (16,400 - 2,425) tons 

 Pb for 16,400 tons 



" (16,400 - 2,425) 1° " 

 16,400 J 



If A = 16,400 tons is taken as l.OOOA, and 

 2,425 tons as SA or 0.1 48 A, 



Pb for (1 

 P 



= P 



■000-0.148)A ^ [" (1.000-0.148) 1°" 

 for 1.000 A L 1-000 J 



= 0.8911 



This gives P^ for 0.852A = 0.8911 (11,902) = 

 10,606 horses. 



The reduction in effective power is only 10.9 

 per cent while the reduction in displacement is 

 14.8 per cent. This appears disappointing. It must 

 be remembered, however, that if the displacement 

 of the given vessel is increased by 14.8 per cent, a 

 similar calculation indicates that the effective 



power of the ship is increased by only 10.45 per 

 cent. 



Using the incremental formula of Eq. (60.ia) 

 without any exponents 



-^ = n(^) = (0.72)(-0.148) = -0.1066 



bPe = -(0.1066)(1 1,902) = -1,269 horses. 



Then Fe for 0.852A = 11,902 - 1,269 = 10,633 

 horses. This is sufficiently accurate for engineering 

 purposes in the design stage. 



J. B. Hadler, G. R. Stuntz, Jr., and P. C. Pien 

 have published not only effective power but shaft 

 power, rpm, wake-fraction, thrust-deduction frac- 

 tion, and other data for three of the five parent 

 models of TMB Series 60, at both 60 and 80 

 per cent of the designed displacement [SNAME, 

 1954, Figs. 9, 10, and 11, pp. 137-139]. These may 

 be compared with data at 100 per cent displace- 

 ment in the same paper. Runs made at zero trim 

 and at the usual trims by the stern for light and 

 ballast conditions at each of these displacements 

 indicated unexpectedly close agreement for all 

 factors except the wake fraction. These data may 



Ship Speed, kt 



Fig. 60.B Variation of Effective and Friction 

 Powers with Change in Displacement and Trim 



Ship Speed, kt 



Fig. 60. C Variation of Effective and Friction 



Powers fob a Tanker, Covering Full-Load and 



Ballast Conditions 



