Class 2 (2nd Engineer) SC&S 📅 Sep 2022

Exam Question

(a) Explain the term Angle of Loll and state the dangers it poses to a vessel. What action to be taken to correct angle of loll (6)

(b) A ship of 22000 tonne displacement is 160m long and MCT 1cm 280 tonne m, waterplane area 3060 m2, centre of buoyancy 1m aft of midship and centre of flotation 4m aft of midships. It floats in water of 1.007 t/m3 at draughts of 8.15m forward and 8.75m aft. (10)

(i) Calculate the new draughts if the vessel moves into sea water of 1.026 t/m3

(ii) Calculate the metacentric height of the vessel

Reference Answer

Angle of Loll refers to the angle of heel at which a ship with negative GM (i.e., unstable equilibrium) comes to rest due to the movement of the center of buoyancy beneath the center of gravity. When a ship with negative metacentric height heels to one side—usually due to an external force like wind or wave action—the center of buoyancy moves toward the lower side. As the heel increases, the center of buoyancy continues to shift outward, and if it moves directly under the center of gravity (G), the capsizing moment is momentarily nullified. The angle at which this occurs is called the angle of loll .
Dangers it poses to a vessel:
The ship oscillates about the angle of loll rather than about the upright vertical, indicating unstable equilibrium.
If the center of buoyancy does not move sufficiently to position itself vertically beneath G, the vessel lacks restoring force and may capsize .

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