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Fin Stabilisers for Controlling Ships Motion

Stabilising fins are fitted to ship's sides below the waterline to reduce rolling of the hull by wave action. The fins achieve this by imposing an equal and opposite motion. Retractable fins of aerofoil section use the forward velocity of the ship to create this opposing motion. As the ship rolls to starboard, the starboard fin is set by a gyroscope signal so that the leading edge of the fin is set above the axis of tilt, giving an upward thrust. The port fin is set in the opposite tilt, with its leading edge below the axis of tilt, giving a downward thrust, and vice versa when the ship rolls to port.

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The purpose of the tail flap on stabiliser fins is to give the fin a more pronounced restoring torque action than if it were a plain surface. The angle of operation of the main fin is 20 degrees at around 15 knots and 11 degrees at around 24 knots. This is to ensure reasonable fin loading.

The angle of operation of the tail flap is 30 degrees. The hydraulic pressure used to house and extend the fin is around 70 ­ 80 bar. and the hydraulic pressure used to alter the fin angle is around 30 bar.

What instrument is used to sense the motion of the ship and then send a signal to the fin controls? : The instrument used to sense the angle of the ship and then send a signal to the fin controls is the roll sensor unit.

The panel fitted to the bridge to monitor fin position is a SOLAS panel, a positive light system to indicate if it is housed or extended. Note: this should also be backed up by visual checks.

Fin stabiliser
Sketch of fin stabiliser set up.



Operational guideline for various auxiliary machinery described here:
Related Info:

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Marine machineries - Useful tags

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