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

Exam Question

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

(b) A bulkhead 9 m deep is supported by vertical stiffeners 750 mm apart. The bulkhead is flooded to the top edge with sea water on one side only. Calculate: (10)

(i) shearing force at top

(ii) shearing force at bottom

(iii) position of zero shear.

Reference Answer

### Part (a): Draught Change between Fresh and Sea Water (6 Marks)
The change in a ship's draught when moving between waters of different densities is governed by Archimedes' Principle, which states that the buoyant force on a submerged or floating object is equal to the weight of the fluid displaced by the object.
1. **Constant Displacement:** The mass of the ship, known as its displacement (Δ), remains constant regardless of the density of the water it is in. For the ship to float in equilibrium, the buoyant force (F_B) must exactly equal the ship's weight (W).
$$ W = F_B $$

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