504

NICHOLLS'S  SEAMANSHIP AND NAUTICAL KNOWLEDGE

in the same position as before, because we must assume that nothing
in the ship has been shifted as the centre of gravity only moves when
weights are moved and, then, in a direction parallel to the direction
in which the centre of gravity of the weight has been moved.
K G is the same as in Figure 25, but the centre of buoyancy has
moved to the low side of the ship owing to her underwater volume
having altered its shape as indicated by the outline of the new
W L K, so the centre of buoyancy must now be a spot a little to the
right of the ship's vertical line at J31.
The ship's weight, indicated by W, acts downwards through 6,
the water buoyancy acts upwards through Bl and its line of action
meets the ship's vertical line at M. This spot is called the metacentre.

The ship at sea oscillates about a rolling axis which is not fixed but
is situated in the vicinity of her centre of gravity at a point a little above
ft The ship, as illustrated in this figure, is said to be in stable equilibrium
because, when forcibly inclined, she will return to her original upright
position when the inclining force is removed. The horizontal distance
between the vertical lines through G and B1 increases, within
limitations, as the angle of heel increases, this distance being
represented by the length of GZ in the figure. GZ is called the arm
and, in this example, a righting lever is being exerted.
The two parallel forces, acting on the lever at the two points & andZ,
form a couple which tends to turn the ship upright again. The moment
is, armXweight, or, GZxW, where GZ is the horizontal distance
between the verticals through G and B1, and W is the total weight of
the ship. The weight of a ship at any draught can be got from her