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Calculating the effect of free surface of liquids (FSE) 199
The following worked example shows the effect of subdivisions in slack tanks in relation to free surface effects (FSE):
Question: A ship has a displacement of 3000 tonnes. On the vessel is a rectangular double-bottom tank 15m long and 8m wide. This tank is partially ®lled with ballast water having a density of 1.025 t/m3.
If the GMT without free surface effects is 0.18 m calculate the virtual loss in GMT and the ®nal GMT when the double bottom tank has:
(a) no divisional bulkheads ®tted;
(b) one transverse bulkhead ®tted at mid-length;
(c) one longitudinal bulkhead ®tted on cL of the tank;
(d) two longitudinal bulkheads ®tted giving three equal divisions.
Answer
Fig. 20.4(a)
FSE virtual loss in GMT or rise in G I rSW W
i.e. unstable ship!!
l b31 rSW 12 W
see Fig: 20:4 a ;virtuallossinGMT 15 83 1:025
3000 12 0:02187m "
; GMT finally 0:1800 0:2187 0:0387m "