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52
THE SUBMARINE TORPEDO BOAT
about the center of buoyancy, tending to right the boat
and acting downwards; the force T, of the water impinging
against the inclined rudders to overbalance the righting
moment W and the upward pull of the reserve buoyancy;
the downward pull of the bow induced by the thrust of
the water against the top of the hull forward of a swinging
line drawn through the center of buoyancy, tending to
upset the boat; and similar forces acting upon the hull
aft of the swinging line tending to keep the boat in equilib-
rium by balancing the forces upon the hull forward of
the swinging line - - the remaining force is the propelling
force of the vessel acting in the direction of the axis of
the ship but unable to effect that direction.
From the relation existing between the contending
forces, it is seen that by vigilance and careful balancing of
the opposing forces, the moment T can be made to govern
the trim of the vessel within certain limits, and the result-
ant thrust of the forces acting upon the hull brought to
balance the upward pull of the reserve buoyancy, the
vessel pursuing a course determined by the resultant of all
the forces.
By observation of the diagram it will be seen that the
swinging line cuts the line of the hull at a point progres-
sively aft of the center of buoyancy as the angle of inclina-
tion increases, thereby projecting a greater area forward
and a lesser area aft to the thrust of the water, with a
constantly increasing overbalancing moment. It will
also be seen that unless kept within very small limits of
inclination this moment will overcome any possible right-
ing moment of the rudders, with a consequent loss of
control and subsequent disaster.
It is because of this fact that it is found impossible to