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64
THE SUBMARINE TORPEDO BOAT
feature is most sought, and is a matter of judgment and
experience of the constructor. If a high surface speed is
sought this may be gained at a sacrifice of submerged
speed or reserve buoyancy, or perhaps by a reduction in
weight of fuel storage and consequent reduction in radius
of action. The weight of the hull is practically Constant
with the displacement, and the apportionment of the other
weights may be varied to meet the ends and fancies of the
constructor. However, a correct balance of surface to
submerged speed and attendant radii of action, and at the
same time have either efficient, can only be attained by
doing away with the dual power system.
This may be more strongly pointed out by considering
for the moment the present tendency to materially in-
crease the size of submarines, having in view the desire
to increase the speed and the radius of action for surface
work. The increase in displacement of course at once
demands proportionately increased engine power. The
power necessary to gain a comparative speed may be ar-
rived at by using Froude’s law of comparison; for instance,
taking a vessel of a displacement of 400 tons and engine
power of 600 B.H.P. which drives her at a 14 knot speed at
full power. To find the power necessary to drive a ship
of 800 tons having otherwise the same characteristics of
contour, appendages, et cetera, the ratio of power would
be,
600
400 * = 1140
800
This does not mean that the two ships would have the
same speed, but that their speeds would be corresponding