CURVE OP BUOYANCY 515
calculated and plotted on their respective ordinates, and the curve of
inetacentres, which is a bold curve, drawn through the spots.
Thus E! MI is the height of the metacentre for '5 feet draught
EZM2 „ „ 10
#3M3 „ „ 15
The vertical distance between the curves gives the BM at any
desired draught.
Thus B1 MI is the B M ior a draught of 5 feet
B2M2 . „ 10 „
£3M3 „ 15 „
A graph for centres of gravity is never given as the V.C.G. alters
with every re-distribution of the weights in the ship, but if the height
of the C. of G. above the keel (K G) is given for certain definite conditions
of loading then those spots could also be plotted on the metacentric
diagram and the G M recorded for at least those particular conditions.
This information is usually worked out for (1) the light load line con-
dition; (2) with water ballast tanks filled and a particular quantity and
distribution of bunkers on board.
Example.—The ship's centre of gravity for the light condition at a
mean draught of 10 feet is computed to be 12 feet above the keel.
Required the metacentric height from the diagram.
Find the 10 feet draught on the horizontal scale; it is at K2. Measure
K% <?2 12 feet upwards and this gives the.position of the 0. of G. The
vertical distance 6r2 M% is the metacentric height required. It measures
3 feet from the scale.
Example.—The C. of G. with ballast tanks and bunkers filled is
computed to be 11 feet above the keel at a mean draught of 15 feet.
Required the GM.
Find the 15 feet draught on the horizontal scale and measure the
height of .the metacentre above the keel; it is
Kz M3 = 14 ft. 6 ins.
#s #3 = 11 ft. 0 ins.
(?3 Mz = 3 ft. 6 ins, the metacentric height required
CARGO AND STABILITY,
It was pointed out on page 506 that the height of the initial centre
of gravity and of metacentre above the keel for the ship in her light
load line condition is supplied by the builder and that this information
offers a starting oft point from which the <? M fox other conditions of