Page 260 - statbility for masters and mates
P. 260
248 Ship Stability for Masters and Mates
Fig. 28.3
There are, thus, three parallel forces to consider when calculating the effect of the force P on the ship's stability. Two of these forces may be replaced by their resultant (see page 4) in order to ®nd the effective metacentric height and the moment of statical stability.
Method (a)
In Figure 28.3 consider the two parallel forces P and (W P). Their resultant W will act upwards through M1 such that:
or
W P y P X
W P MM1 siny P KM1 siny W P MM1 P KM1
W MM1 P MM1 P KM1
W MM1 P KM1 P MM1
P KM1 MM1 P KM
MM1 P KM W
There are now two forces to consider: W acting upwards through M1 and W acting downwards through G. These produce a righting moment of W GM1 siny.
Note also that the original metacentric height was GM but has now been reduced to GM1. Therefore MM1 is the virtual loss of metacentric height due to drydocking.
