8.(a) State TWO types of Tank Anti-Roll Stabiliser systems.(2)
(b) State the advantages and disadvantages of a stabilising tank system compared to fin stabilisation.(8)
Construction (5 marks)
- Two wing tanks (port and starboard) are fitted at the top of the ship, connected by a cross-duct.
- A central control tank or header tank is located amidships.
- Butterfly valves / throttling valves are fitted in the cross-duct and controlled automatically.
- Pumps may assist water transfer in some designs, but many systems rely on gravity and roll inertia.
- A control system (gyro sensor + feedback unit) monitors vessel roll motion and adjusts valve openings accordingly.
Operation (5 marks)
- When the vessel rolls, water in the active tank system is made to move out of phase with the ship’s roll.
- The control valves open and close in response to roll angle and velocity, as detected by the gyro.
- Water shifts between the port and starboard tanks, creating a counter-moment to oppose roll.
- This damps roll amplitude significantly compared with passive tanks, since flow is actively regulated.
- The system can be tuned to different sea states and vessel speeds, providing greater efficiency than a passive free-surface tank.
Sketch (exam-style)
- A ship cross-section with:
- Port & starboard wing tanks, labelled.
- Cross-duct with controlled valve.
- Central control/header tank.
- Arrows showing water transfer direction during roll.
- Gyro sensor symbol with link to valve control.