218 THE PROBLEM OF THE HULL AND ITS SCREW PROPELLER. 
result, when the projected area ratio of the model screw was kept equal to that of the 
original propeller, in a propeller of less diameter than his model propeller, of very much 
lower pitch and of exceedingly high revolutions. Should he hold the diameter equal 
to that of his model screw, the pitch obtained will be much lower than that of the model 
and the projected area ratio much smaller. 
Should he, however, apply the law of comparison to the factors used in designing 
the propeller for the ship, assuming that wake remains constant and that the frictional 
resistance of the hull follows the law of comparison, which it does not, he would obtain 
the proper factors for use in designing the model propeller, as, for example :— 
Ship Ratio Model 
Tals Wakes 
Length on load water line.......... L. L. W. L. R ma 
NT I v 
Speed Ob Ship i omerrr newletter. v Rie Rie 
; I e. h. p. 
Effective horse-power forv......... e.h. p. Re Re 
IDadelele: 
Basic effective horse-power.......... 195 Jaly 12) = 5 R? 
TBI, 12 
Basic horse-power (engine or shaft) EP: a = R? 
‘ eh. p. I e. h. p 
oadtiractiony Nera aon mer cee EHP. RE R® x E.EP 
; v I v 
Speed Mractionmnenne erent V Re ReV 
IBasicrappanenitns Lhe eeieeeiciek S I Ss 
; I D 
Diameter of propeller.............. D R aa 
: I Ie 
Pitchionpropellemenen nee teeenee I2 R Man 
k : PAL Rae 
Projected area ratio of propeller..... D.A. I Daal 
Taking these values in the equations for power; for ship :— 
(2) Log H. Pi, = Log TH. PR) —'Z- 
For model: 
Log h.p.q = Logh. p. — Zye 
BE. HEP: : 
Zpg = 1.0414 Log (GE) for ship. 
adel, Jey le 1B, Tal, 12. 
Zpg = 1.0414 Log ({ aie! x xe) = 1.0414 Log (2e*) +1.0414 X = Log R 
