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

Exam Question

A virtual rise in the centre of gravity of a ship may be caused by

(a) Filling a partially filled tank

(b) Using an onboard crane to lift a freely swinging heavy object

(d) Transferring pipe from the setback area to the pipe rack

Briefly Justify your Answer. (16)

Reference Answer

The correct option is **(c) Emptying a partially filled tank**.
### Justification
A 'virtual rise in the centre of gravity' is a concept in naval architecture used to quantify a reduction in a ship's stability. It does not represent a physical movement of the ship's centre of gravity (G), but rather an effective rise to a new position (Gv). The ship's stability characteristics, specifically the righting lever (GZ) and metacentric height (GM), are reduced as if G had physically risen. This phenomenon is primarily caused by the **Free Surface Effect (FSE)**.
#### 1. Core Concept: The Free Surface Effect (FSE)

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