Class 4 (4th Engineer) SC&S 📅 Jan 2023

Exam Question

(a) List the causes for impairment of stability of a vessel. (6)

(b) A box-shaped vessel floats upright on an even keel as shown in fresh water of density 1000 kg per cubic meter, and the center of buoyancy is 0.50 m above the keel. Find the height of the center of buoyancy above the keel when the vessel is floating in salt water of density 1025 kg per cubic meter. (10)

Reference Answer

### Part (a): Causes for Impairment of Stability of a Vessel (6 Marks)
The stability of a vessel, its ability to return to an upright position after being heeled by an external force, can be impaired by several factors. These factors typically act by either raising the vessel's center of gravity (KG), reducing the metacentric height (GM), or introducing external heeling moments that overwhelm the vessel's righting capability.
1. **Free Surface Effect:**
* **Mechanism**: When a tank or compartment is partially filled with liquid, the liquid is free to move as the vessel rolls. This movement of the liquid's center of gravity effectively creates a 'virtual rise' in the ship's overall center of gravity (G to Gv), leading to a reduction in the effective metacentric height (GM to GvM) and a corresponding decrease in the righting lever (GZ).

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