An oil tanker of 17000 tonne displacement has its centre of gravity 1 m aft of midships and has 250 tonne of oil fuel in its forward deep tank 75 m from midships. This fuel is transferred to the after oil fuel bunker whose centre is 50 m from midships. 200 tonne of fuel from the after bunker is now burned.
Calculate the new position of the centre of gravity: (a) after the oil has been transferred (b) after the oil has been used.
Given
Displacement = 17000 t
mf = 250 t
df = 75 m fwd of midship
KG = 1m aft of midship
ma = 200 t
da = 50 m fwd
To find
1. COG after transfer
2. COG after consumption
Solution
1) Case 1 after transfer
We know that shift in COG = mass moved x distance / Displacement
= 250 x (75 +50) / 17000
= 1.838 m aft
The new position of COG = old COG + shift in COG
= 1 + 1.838
= 2.838 m aft
2) Case 2 after consumption
New position of COG = (Displacement x KG) - (ma x da) / (17000 - 200)
= (17000 x 2.838) - (200 x 50) / 16800
= 2.277 m aft
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