562
Molesworth's pocket-book
Elementary Relation between Pitch, Slip, and Propvl-
sive Efficiency. (Fronde, ‘Inst. Nav. Arch.,’ 187«.)
A — Area of propelling plane surface in square feet.
P =z Normal pressure on a plane area moving on a path
forming the angle 0 with the plane, in lbs.
p = Coefficient of pressure, lbs. per square foot — abotrt 1-7.
y — „ skin friction ,, = „ ’008
(being • 004 for each surface).
lc — L— '0047 appproximately.
” ■ p ‘ ‘ '
F =. Friction on surface of plane moving edgeways = Kfv2.
V = Speed of propeller plane, feet per second.
v = Speed of vessel in feet per second.
=e Speed of plane through water, feet per second.
s = Speed of slip. __
0 = Slip angle =± V fc for maximum efficiency.
a = Virtual pitch angle.
<j> =: Actual „ „ = a + 9.
R = Propulsive force to maintain speed of ship, lbs.
W — Gross work done, foot-lbs.
w = Effective „ „ = Ri’ = R V tan. a.
E = Efficiency = W —- w — about -11 hs a maximum.
Slip ratio = — ; P =p A v2 sin. 0 ;
v + s
W = j) A Vs sec.® a (sin. <f> sin. 0 + k cos. a);
_____________________R __________________
pv2 cosec.’2 a (cos. </> sin. 0 — k sin. a)