220 THE PROBLEM OF THE HULL AND ITS SCREW PROPELLER. 
For model: 
us UX I0T.33 TREES. Tote 83) 
Talis RP. 5 ~ Px (RBs) 
R* xEx(1— pu) 
from which by assuming any desired value of R and the known value s from trials of 
of the ship, the revolutions for the model can be obtained, or vice versa. 
Ra x R-®'6 (1s) 
Ue) JRookiO aay & 
To obtain the apparent slip and revolutions of the actual propeller from the per- 
formance of the model, the equations become 
s = 5 R-1316 
and 
DEOL ES 
Re ID (Gag IES )) 
ue v X 101.33 2 VREECD SS tiem g3)) 
aan P eae) 
Ios (8) mass 
ee, (1-s) 
R 1/2 (1-s R -1316 ) 
depending for its value on R and s. 
The actual powers and revolutions for the model will probably be higher than those 
obtained by these equations as the actual effective horse-power is greater than that 
obtained by the law of comparison and the wake of the model is probably different from 
that of the ship. 
To illustrate the above take first the vessel in the first column of Problem 1 and 
deduce the model propeller and its performance from the actual by the above formulas, 
then analyze and estimate the performance of the model screw by the ordinary method. 
Conditions of Problem:—Speed of ship=11 knots; e.h. p. = 1160; R = 30 
Analysis Comparison Analysis 
ID) (GIy. Oh aso 
P= 14.75 Pp = .492" 
PA TPM he 
DU a DU ge a 
T.S. = 6230 T.S. = 6230 
1-S = .86 1—S = .86 
Ves TA Of V = 14.97 
I. T.p=3.09 Moy) SS S010) 
Wedel TEs = Gucci ih. p.= bee = 5.708 5.7072 
P.C. = 606 P.C. = .696 .696 
