N. B. B. 263-16
INCLINING EXPERIMENT, U. S. S.
feet above base line
Vessel considered water-tight to
Taken from Plan No.
Scale of Tons Displacement
Figure 12-26. Example of cross curves of stability.
ship's center of gravity (G). To use a curve taken from
read the corresponding value of the righting arm on the
vertical scale at the left. Then plot this value of the
the cross curves, therefore, it is necessary to correct the
righting arm at the corresponding angle of heel on the
curve for the ACTUAL height of G above the keel
grid for the stability curve. When you have plotted a
(KG). If the distance KG is not known and a number of
series of such values of the righting arms from 10° to
weights have been added to or removed from a ship,
90° of heel, draw a smooth line through them and you
KG can be found by the use of vertical moments. A
have the UNCORRECTED stability curve for the ship
vertical moment is the product of the weight times its
at that particular displacement.
vertical height above the keel. As far as the new center
In figure 12-27, curve A represents an uncorrected
of gravity is concerned, when a weight is added to a
stability curve for the ship while operating at
system of weights, the center of gravity can be found
11,500 tons displacement, taken from the cross curves
by taking moments of the old system plus that of the
shown in figure 12-26. This stability curve cannot be
new weight and dividing this total moment by the total
used in its present form, since the cross curves are
final weight. Detailed information concerning changes
made up on the basis of an assumed center of gravity. In
in the center of gravity of a ship can be obtained from
actual operation, the ship's condition of loading will
Naval Ships' Technical Manual (NSTM), chapter 096.
affect its displacement and therefore the location of the