read the corresponding value of the righting arm on the
vertical scale at the left. Then plot this value of the
righting arm at the corresponding angle of heel on the
grid for the stability curve. When you have plotted a
series of such values of the righting arms from 10° to
90° of heel, draw a smooth line through them and you
have the UNCORRECTED stability curve for the ship
at that particular displacement.
In figure 12-27, curve A represents an uncorrected
stability curve for the ship while operating at
11,500 tons displacement, taken from the cross curves
shown in figure 12-26. This stability curve cannot be
used in its present form, since the cross curves are
made up on the basis of an assumed center of gravity. In
actual operation, the ship’s condition of loading will
affect its displacement and therefore the location of the
ship’s center of gravity (G). To use a curve taken from
the cross curves, therefore, it is necessary to correct the
curve for the ACTUAL height of G above the keel
(KG). If the distance KG is not known and a number of
weights have been added to or removed from a ship,
KG can be found by the use of vertical moments. A
vertical moment is the product of the weight times its
vertical height above the keel. As far as the new center
of gravity is concerned, when a weight is added to a
system of weights, the center of gravity can be found
by taking moments of the old system plus that of the
new weight and dividing this total moment by the total
final weight. Detailed information concerning changes
in the center of gravity of a ship can be obtained from
Naval Ships’ Technical Manual (NSTM), chapter 096.
read the corresponding value of the righting arm on thevertical scale at the left. Then plot this value of therighting arm at the corresponding angle of heel on thegrid for the stability curve. When you have plotted aseries of such values of the righting arms from 10° to90° of heel, draw a smooth line through them and youhave the UNCORRECTED stability curve for the shipat that particular displacement.In figure 12-27, curve A represents an uncorrectedstability curve for the ship while operating at11,500 tons displacement, taken from the cross curvesshown in figure 12-26. This stability curve cannot beused in its present form, since the cross curves aremade up on the basis of an assumed center of gravity. Inactual operation, the ship’s condition of loading willaffect its displacement and therefore the location of theship’s center of gravity (G). To use a curve taken fromthe cross curves, therefore, it is necessary to correct thecurve for the ACTUAL height of G above the keel(KG). If the distance KG is not known and a number ofweights have been added to or removed from a ship,KG can be found by the use of vertical moments. Avertical moment is the product of the weight times itsvertical height above the keel. As far as the new centerof gravity is concerned, when a weight is added to asystem of weights, the center of gravity can be foundby taking moments of the old system plus that of thenew weight and dividing this total moment by the totalfinal weight. Detailed information concerning changesin the center of gravity of a ship can be obtained fromNaval Ships’ Technical Manual (NSTM), chapter 096.
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