520

NICHOLLS'S SEAMANSHIP AND NAUTICAL KNOWLEDGE

The height of the metacentre above the centre of buoyancy is

—ire

Where L is the ship's length and D the draught tor box-shaped
vessels.

Fig. 38.
Figure 38 represents a ship tipped by the head by some external
force. B moves to Bl but the C. of G remains at G as no alteration
has been made in the distribution of weights in the ship. M is the
point where the vertical line through the new C. of B. intersects the
vertical line through the original C. of B. and this defines the longitudinal
metacentre. GZ is the arm of the moment tending to bring the ship
back to an even keel and, as in the case of transverse inclinations, the
moment will be WxOZ.
The draught of a ship is given at the stem and stern and there seems
no particular reason why it should not also be given amidships. The
draught figures are § inches in depth and the space between them
is also 6 inches.
When the draught is greater at one end than the other the ship is
said to be trimmed so much by the head, or by the stern, as the case
may be.
The tipping* centre is assumed to be at the middle of the vessel's
length for approximate calculations involving small changes of trim.
If a weight (w), say 90 tons, be placed exactly over the tipping centre
(T.C.) the ship will sink bodily and, if her tons per inch immersion