Page 213 - statbility for masters and mates

Calculating the effect of free surface of liquids (FSE) 201
Fig. 20.4(d)
GMT is now ve, but below the minimum GMT of 0.15m that is allowable by D.Tp. regulations.
FSE virtual loss in GMT or rise in G 3@l1 b3 rSW (see Fig. 20.4(d)) 12 W
8 3 3 15 3 1:025
; Virtual loss in GMT 12 W
0:0243 m " i.e. 19 of answer to part (a)
Hence
final GMT 0:1800 0:0243 0:1557 m ship is stable.
Ship is stable and above D.Tp. minimum GMT value of 0.15 m.
So longitudinal divisional bulkheads (watertight or wash-bulkheads) are effective. They cut down rapidly the loss in GMT. Note the 1/n2 law where n is the number of equal divisions made by the longitudinal bulkheads.
Free surface effects therefore depend on:
(I) density of slack liquid in the tank; (II) ship's displacement in tonnes;
(III) dimensions and shape of the slack tanks; (IV) bulkhead subdivision within the slack tanks.
The longitudinal divisional bulkheads referred to in examples in this chapter need not be absolutely watertight; they could have openings in them. Examples on board ship are the centreline wash bulkhead in the Fore Peak tank and in Aft Peak tank.