Class 2 (2nd Engineer) SC&S 📅 Jan 2024

Exam Question

(a) With reference to dynamical stability, describe the effect of an increase in wind pressure when a vessel is at its maximum angle of roll to windward. (6)

(b) An oil tanker 160 m long and 22 m beam floats at a draught of 9m in sea water. Cw is 0.865. The midship section is in the form of a rectangle with 1.2 m radius at the bilges. A midship tank 10.5 m long has twin longitudinal bulkheads and contains oil of 1.4 m3/t to a depth of 11.5 m. The tank is holed to the sea for the whole of its transverse section. Find the new draught. (10)

Reference Answer

(a) Dynamical Stability is defined as the amount of energy required to heel a ship from its upright equilibrium position to a specific angle of heel. It provides a measure of the vessel's stability by considering its behaviour in response to dynamic external forces , such as wind or waves.
The concept compares the heeling moment energy (from external forces) and the righting moment energy (from the ship's stability).
The ship will absorb the energy imparted by the heeling moment. If the righting energy is greater than the heeling energy, the ship will stabilize; otherwise, it may capsize.
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