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

Exam Question

(a) Explain 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 Variation with Water Density
#### Fundamental Principle
The change in a ship's draught when moving between fresh water and seawater is governed by Archimedes' Principle. This principle states that the buoyant force acting on a submerged or floating body is equal to the weight of the fluid displaced by the body. For a floating ship, the buoyant force must equal the total weight of the ship (its displacement).
The ship's mass (and therefore its weight or displacement, Δ) remains constant regardless of the water it is in. The relationship is expressed by the formula:

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