CHAPTER XVIit

STABILITY, CARGO AND TRIM

LEVERS.

Practical seamanship in many of its branches is an application of
some of the elementary principles of mechanics and hydrostatics.
Every person when moving his limbs intuitively applies some principle
of mechanics either in preserving his equilibrium, overcoming the force
of gravity or moving a weight. The human frame is a machine.

Let us refer briefly to some fundamental notions in mechanics.

The Moment of a force is its power to cause rotation. The simplest
form of schoolroom apparatus for demonstrating the law of moments
is a flat wooden ruler graduated in inches, supported on a nail through
a hole at its centre so that it is perfectly balanced but free to rotate in the
vertical plane about this axis called the Fulcrum (F).

When a 1-lb. weight (W) is hung at a distance of 12 inches to the
right of the fulcrum (F), the right hand end of the ruler at once turns
clockwise. The weight (W) is called the Force, and the distance (F W)
the Arm.
The Moment of the force round the "fulcrum is therefore 12 ins. xl lb.
=12 inch-lbs., or, 1 ft.xl lb.=l foot-lbs.
If a weight (F1) of 3 Ibs. be now hung at a distance of 4 inches to
the left of the fulcrum F, the ruler will turn counter-clockwise and one
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