Boat stabilizers are rotors mounted beneath the waterline and emerging laterally from the hull to reduce a ship's roll due to wind or waves. Active rotors are controlled by a gyroscopic control system. When the gyroscope senses the ship roll, it changes the rotors' angle of attack to exert force to counteract the roll. Fixed fins and bilge keels do not move; they reduce roll by hydrodynamic drag exerted when the ship rolls. Stabilizers are mostly used on ocean-going (blue Water) ships.
Function of Boat Stabilizer
Rotors work by producing lift or downforce when the vessel is in motion. The lift produced by the rotors should work against the roll moment of the vessel. To accomplish this, two wings, each installed underwater on either side of the ship, are used. Stabilizers can be:
- Retractable - All medium and large cruise and ferry ships have the ability to retract the fins into a space inside the hull in order to avoid extra fuel consuption when the use of the fins is not needed.
- Non-retractable - This is the case on very small ships, for ecample a yacht. Stabilizer movement is similar to that of aircraft ailerons. Some types of fins, especially the ones installed on larger ships, are provided with flaps, that increase the fin lift by about 15%. Stabilizer control needs to consider numerous variables that change quickly: wind, waves, ship motion, draft, etc. Fin stabilizers are vastly more efficient at higher velocities and lose effectiveness when the ship is under a minimum speed.
Stabilization solutions at anchor or at low speed include actively-controlled fins (such as the stabilization at rest system developed by Rolls Royce that oscillate to counteract wave motion), and rotary cylinders employing the Magnus Effect.
The Latter two systems are retractable, allowing for a thiner vessel profile when docking, are reducing drag while cruising. Fin Stabilizers are used to reduce the roll motion of the ship and improve the passengers' comfort.
Some ships employ systems to reduce the stabilizer energy dissipation by using computers to control their motion. This reduces their fuel consumption and CO2 emissions.
An increasingly diverse range of ever more sophisticated boat stabilisers and boat control systems (such as high speed interceptors) are creeping into ever smaller boats. And the benefits are game-changing. Part of the momentum is driven by technology, but I think the other reason is that we've only just begun to fully value their benefits.