Class 4 (4th Engineer) SC&S 📅 Jul 2025

Exam Question

(a) Show by means of diagrams how the center of gravity of the liquid in a partly filled tank moves during rolling. (6)

(b) A box barge is 15 m long, 6 m wide and floats in water of 1.016 t/m³ at a draught of 3 m. 150 tonne of cargo is now added. Calculate the load exerted by the water on the sides, ends and bottom. (10)

Reference Answer

### Part (a): Movement of Center of Gravity in a Partly Filled Tank
#### Concept of Free Surface Effect
When a vessel with a partly filled tank (a slack tank) is inclined by an external force (e.g., wind, waves), the liquid within the tank, being free to move, will tend to remain level. This movement of liquid results in a shift of the tank's center of gravity, which in turn adversely affects the vessel's stability. This phenomenon is known as the **Free Surface Effect (FSE)**.
#### Movement During Rolling

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