Class 2 (2nd Engineer) SC&S 📅 Apr 2019

Exam Question

With respect to Buoyancy of a vessel:

(a) What do you understand by reserve buoyancy what happen if the lost buoyancy is greater than the reserve buoyancy. (6)

(b) A forward deep tank 12 m long extends from a longitudinal bulkhead to the ship's side. The widths of the tank surface measured from the longitudinal bulkhead at regular intervals are 10, 9, 7, 4 and 1 m. Calculate the second moment of area of the tank surface about a longitudinal axis passing through its centroid. (10)

Reference Answer

(a) Reserve Buoyancy
Reserve buoyancy is the watertight volume above the waterline of a vessel. It represents the potential buoyancy that can be utilised to keep the ship afloat when additional weight is added or if some buoyancy is lost due to damage (e.g., bilging).
When a mass is added to the ship or buoyancy is lost (e.g., due to flooding of a compartment), the reserve buoyancy is converted into active buoyancy by an increase in draught .
If the lost buoyancy (due to flooding or damage) is greater than the reserve buoyancy , the vessel will no longer have sufficient buoyant force to counteract its weight, causing it to sink .

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