5G0 Molesworth’s pocket-book
I’brssurk of Water on an Oblique Surface relativf.lt
Marrow in the Line of Motion. (Lord Rayleigh.)
p = Normal pressure acting on the face of the plane.
P = Pressure of a head due to the speed acting on the
plane.
a = Angle between the plane and the line of motion.
P (4 + tt) sin. a
P - —-------------•
4 + tt sin. a
Froude is of opinion that as it appears by Beaufby’s ex-
periments that when the plane is moving normally through
tlie water so that a = 90° the resistance actually exceeds P
in the ratio of 112 to 96, (or say 1'00 to -86), it is not im-
probable that a proportionate excess beyond p as given in
Lord llayleigh’s formula will be experienced when the
motion is oblique.
Resistance of Vessels. (Froude.)
For moderate speeds, the resistance of a ship is proportional
io the “indicated thrust” + a constant, which represents
the dead-weight friction uf the engines, &c.
_______________________ 33,000 P.
1 he “ indicated thrust = —-----— ,
S n ■
where P = Indicated horse-power,
S = Pitch of screw in feet,
n = Number of revolutions per minute.
From experiments with models, the following rule has
been adduced,:—
If the ship’s dimensions be D times those of the model,
P ±= Indicated horse-power of the model,
V = Velocity of ditto;
then for speed V 1) . V of the ship the power will be
])3 p y' J). And if at speeds V-[, V?, Vg, the measured resist-
ances be lij, 1<2, and J!3 respectively, the resistances of the
ship will be D3 Rj ; D3 Ro; I)3 R3 respectively.
Jn experiments with fl.M.S. ‘Greyhound,’ it was found
that about 58 per cent, of power was wasted in friction of
machinery, and in detrimental action caused by the screw in
the water at the stern of the vessel.
Lightening and thus diminishing the displacement did not
seem to be proportionally advantageous.