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40
THE SUBMARINE TORPEDO BOAT
marine type; both types in fact have been modified — the
submarines by increasing the amount of reserve buoyancy
and by enlarging the superstructures; and the submers-
ibles by decreasing to some extent the size of the super-
structures and the excessive amount of reserve buoyancy,
so that now the best practice seems to be to provide a
reserve buoyancy of from about twenty to thirty per cent
for both types.
A great deal of contention has been made by the adher-
ents to one or the other of these forms as to the inherent
advantages and disadvantages of each, so it might be well
to discuss from an impersonal point of view the relative
values of each.
'I'he question of stability seems to be the main point of
contention between the two. Along this line it is quite
evident that the ship form of hull of the submersible will
have a greater longitudinal stability when on the surface
due to its metacentric height, which in this case is similar
to an ordinary ship, the center of gravity being above the
center of buoyancy on account of the relatively high posi-
tion of the centers of gravity of the hull and the machinery
weights. The surface stability then, in this case depend-
ing upon the inertia of the water plane areas and form,
results in a short rolling period.
In the single hull construction of circular cross section
of the submarine proper, it will be immediately seen that
the position of the center of gravity of the hull is well below
the axis and the machinery weights can be kept lower.
In this case the position of the metacenter coincides with
that of the center of buoyancy, due to the circular form of
cross section, and with the non-watertight superstructure
this relation is always constant no matter what angle of