580 W. J. Marwood and A. Silverleaf 
- 0-02 
-0-01 
oo SHIP (TONS) 
+0-01 
+0-02 
{00 
LENGTH (FT) 
Fig. 16. Values of & and of Froude’s “0” for a round-bilge boat 
decreasing at higher speeds, finally approaching open water conditions. The wake fraction 
w is small, as expected, and slightly negative at high speeds. 
From these factors and the propeller open water efficiency 7)» Which depends princi- 
pally on the permissible propeller diameter or the engine-propeller gear ratio, the quasi- 
propulsive coefficient 7 can be estimated as 
71 = No IR: 
Ship-Model C omparison 
Good data from full-scale trials under ideal conditions are required to determine the 
correlation factors linking predicted performance from model experiments with that measured 
on shipboard. Little reliable data for high speed displacement-type forms are available, and 
