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50
THE SUBMARINE TORPEDO BOAT
of action, and possessed but very slow speeds. In the
longer boats intended for the diving type it was found
that to get these boats under water with even a small per-
centage of reserve buoyancy, it necessitated so great a
turning moment by means of the stern diving rudders,
that when once the boat was gotten under way it was very
apt to lose control of her and end in disaster. The for-
ward diving rudders were then put into use to meet this
contingency and to neutralize the effects of the plunging.
The still greater amount of reserve buoyancy which is
carried under by the “even keel” boat, it is easily demon-
strable, demands the hydroplane method of submergence.
These broad planes, together with the effect of the trim-
ming rudders aft to aid in preserving a horizontal equilib-
rium, tend to give in some degree a greater safety in
performing the operation of submerging, theoretically
at least.
In the diving type then the method of submergence has
finally resolved into an inclined movement part way be-
tween a dive and a vertically oblique movement, and in
the “even keel” boat the submergence may be said to be
in an entirely oblique direction. It is quite evident there-
fore, that to obtain this latter motion it must be at the
expense of a great amount of power and in a necessarily
sluggish manner, for the vessel is being forced in a direction
that projects its greatest area to the contrary thrust of
the water, which must of necessity detract from the sub-
merged speed. To overcome this in the slightest degree
means that the vessel must be inclined by the head one
or two degrees, and thereby presenting the broad expanse
of the superstructure deck to aid in acting as a submerging
plane. The increased safety factor of this type over the