Exam Question
(a) Explain the Operational principle of a ship's stabiliser.
(8)
(b) Describe with sketches Active and Passive types of stabilizers.
(8)
Class 2 (2nd Engineer)
MEKG
📅 Jan 2026
Reference Answer
### (a) Operational Principle of a Ship's Stabiliser (8 Marks)
The fundamental operational principle of a ship's stabiliser is to generate a righting moment that actively opposes the rolling moment induced by wave action. This significantly dampens the amplitude and velocity of the ship's roll, enhancing safety, comfort, and operational efficiency.
The principle can be broken down into the following key stages, primarily focusing on the most common active fin type:
1. **Hydrodynamic Lift Generation**: The core of the system is the generation of hydrodynamic force (lift). Stabiliser fins are shaped as hydrofoils. When moved through the water at an angle relative to the flow, known as the **Angle of Attack (AoA)**, a pressure differential is created between the upper and lower surfaces. This results in a net force (lift) perpendicular to the direction of water flow.
The fundamental operational principle of a ship's stabiliser is to generate a righting moment that actively opposes the rolling moment induced by wave action. This significantly dampens the amplitude and velocity of the ship's roll, enhancing safety, comfort, and operational efficiency.
The principle can be broken down into the following key stages, primarily focusing on the most common active fin type:
1. **Hydrodynamic Lift Generation**: The core of the system is the generation of hydrodynamic force (lift). Stabiliser fins are shaped as hydrofoils. When moved through the water at an angle relative to the flow, known as the **Angle of Attack (AoA)**, a pressure differential is created between the upper and lower surfaces. This results in a net force (lift) perpendicular to the direction of water flow.
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