Class 2 (2nd Engineer) SC&S 📅 Jan 2019

Exam Question

(a) Explain the effects on stability when a tank is partially filled with liquid. (6)

(b) A ship of 11200 tonne displacement has a double bottom tank containing oil, whose centre of gravity is 16.5m forward and 6.6m below the centre of gravity of the ship. When the oil is used the ship's centre of gravity moves 380mm. Calculate: (10)

(i) The mass of oil used

(ii) The angles which the centre of gravity moves relative to the horizontal.

Reference Answer

(a) Slack tanks, or partially filled tanks, significantly impact a ship's stability due to the free surface effect
When tanks are partially filled (slack), the liquid inside moves freely as the ship heels.
This movement shifts the centre of gravity (G) laterally towards the heeling side.
The righting lever ( GZ ) decreases, resulting in reduced metacentric height (GM) and overall stability.

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