Class 4 (4th Engineer) SC&S 📅 Aug 2022

Exam Question

(a) Explain why the draught of a ship decreases when it passes from fresh water to sea water and vice versa (6)

(b) A lock gate which is 15m wide has salt water on one side to a depth of 8m and fresh water on the other side to a depth of 9m. Find the resultant thrust on the lock gate and state on which side of the gate it acts (10)

Reference Answer

### (a) Change in Draught between Fresh Water and Sea Water
#### Fundamental Principle
According to Archimedes' principle, a ship floats when the upward buoyant force exerted on it by the water is equal to the downward force of the ship's total weight. This total weight is referred to as the ship's displacement (Δ).
The buoyant force is equal to the weight of the volume of water displaced by the ship's hull. This relationship can be expressed by the formula:

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