Page 209 - statbility for masters and mates

Calculating the effect of free surface of liquids (FSE) 197
Hence G1 has risen due to the discharge of the ballast water (loading change) and has also risen due to Free Surface Effects.
Be aware that in some cases these two rises of G do not take G above M thereby making the ship unstable.
Example 2
A ship of 6000 tonnes displacement, ¯oating in salt water, has a double bottom tank 20 m 12 m 2 m which is divided at the centre line and is partially ®lled with oil of relative density 0.82. Find the virtual loss of GM due to the free surface of the oil.
VirtuallossofGM i roil 1 W n2
lb3 11 12 roil W n2
20 123 1 12 6000 0:820 22
Ans. Virtual loss of GM 0:098 metres
Example 3
A ship of 8000 tonnes displacement has KM 7.5 m, and KG 7.0 m. A double bottom tank is 12m long, 15m wide and 1m deep. The tank is divided longitudinally at the centre line and both sides are full of salt water. Calculate the list if one side is pumped out until it is half empty. (See Fig. 20.3.)
Mass of water discharge lDB bDB dDB rSW 2
Mass of water discharged 12 7:5 0:5 1:025 w 46:125 tonnes
Vertical shift of G(GG1) w d W2
46:125 6:25 46:125 6:25
8000 46:125 0:036 metres
Horizontal shift of G(GvG2) w d W w
46:125 3:75 7953:875
7953:875
0:022 metres Virtual loss of GM(G1Gv) l b32 rSW 1
12 W2 n2
12 7:53 1:025 1
12 7953:875 12 0:054 metres