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DESIGN OF THE SUBMARINE TORPEDO BOAT 77
. . _ I.H.P. X 132000
I .T a per square inch disc area — P.X R—X 7
E.T.p effective thrust in pounds per square inch on pro-
E.H.P. x 33000
jected area = o--------------D—.—.—
1 S. X 101.33 X P.A. in in.
The reader is here referred to the work of Captain C. W.
Dyson, U.S.N. entitled, Screw Propellors and Estimation
of Power for Propulsion of Ships, which is a complete and
comprehensive treatise upon the estimation of power and
the design of screw propellors.
Another method of computing the power for propulsion
is by Froude’s Laws of Comparison. This method offers
a very simple and expedient way of solving the problem
when the actual performances of a geometrically similar
vessel are known.
The rules governing this method of computation are:
1. Corresponding Speeds
S:S1= VL:VL1= S= S VL
Lt
2. Displacements
D : DI= 13: L13= D) = ---
3. Corresponding Speeds
S:S1= VD:VD = S= sV=
Di
4. Horsepowers
________6/DT
P:P1= VDT:VD = P = P.V —
This law is, however, not strictly correct.