SHIP   STABILITY

503

smaller will be her coefficient. In destroyers, yachts and vessels wneie
great speed is required the coefficient may be as small as 45, whereas
in the bluff tramp class where speed is a secondary consideration the
coefficient is often as great as -85. Between these two extremes the
coefficient of fineness is adopted to suit the requirements of the vessel.
SHIP STABILITY,
Draw a cross section of a ship with a waterlme across it. Mark a
spot G to represent the centre of gravity of the ship which is a point
where the whole weight of the ship and her contents are conceived to
act vertically downwards, Mark a spot B to represent the centre of
buoyancy of the ship. It is the point at the centre of the displaced
volume of water through which the whole supporting force of the water
is conceived to act vertically upwards. It will be the geometrical
centre of the figure W L K.

w

q
b*

Fig. 25,
The downward force at 6 is equal to the upward force at B. They
are equal and opposite forces acting in the same vertical line when the
ship is at rest. When they are not in the same vertical line something
must happen as the ship cannot remain at rest as she wants, auto-
matically, to return to her position of equilibrium. In Figure 25 K <ris
the height of the centre of gravity above- the keel, and K B the height
oi the centre of buoyancy above the keel.
(i) Stable Equilibrium.—Figure 26 represents the same ship forcibly
xoclined by an external force such as wind pressure, rolling at sea or by
a masthead tackle led ashore somewhere. The centre of gravity i&