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DESIGN OF THE SUBMARINE TORPEDO BOAT 6i
of the total weight of the ship. To attain this object the
superstructure must be as light as good practice will permit
and all weights above deck must be kept as small as pos-
sible. The shell plating should be made heavier at the
keel to give stiffness against “hogging” and be tapered
down to the required thickness at the top of the hull for
resistance against the pressure of submersion.
Great care should be exercised in the distribution of
weights, for, unlike a surface vessel, with a comparatively
small reserve buoyancy present and especially in a sub-
merged condition when the buoyancy is practically des-
troyed, the submarine is suspended like a balance scale
and must be in equilibrium in a horizontal position. The
balancing moments about this point must be gained as far
as possible by the distribution of all machinery, equipment
and fixed articles, because the displacement limitations
allow only a relatively small amount in weight of perma-
nent ballast to be utilized, which can be of but little
assistance in effecting the trim.
All machinery and battery weights must be kept as low
as possible and as is consistent with good practice and
accessibility, for the center of gravity of the completed
ship can be much affected by their positions, and the laws
of submarine navigation demand that the center of gravity
and the center of buoyancy be kept as far apart as possible.
Ballast System
A general principle applicable to all submarines is the
destruction of reserve buoyancy to submerge, by taking
on additional weight in the form of water ballast. The
main ballast system, whether in one tank centrally located
or comprised of fore and aft tanks, is designed to nearly