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Ship stabilizers are fins or rotors mounted beneath the waterline and emerging laterally from the hull to reduce a ship's roll due to wind or waves. ''Active fins'' are controlled by a gyroscopic control system. When the gyroscope senses the ship roll, it changes the fins' 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== Fins work by producing lift or downforce when the vessel is in motion. The lift produced by the fins should work against the roll moment of the vessel. To accomplish this two wings, one 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 consumption when the use of the fins is not needed. * Non-retractable - This is the case on very small ships, for example 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 ''stabilisation at rest'' system developed by Rolls Royce〔(【引用サイトリンク】title=Stabilisation at rest )〕 that oscillate to counteract wave motion), and rotary cylinders employing the Magnus effect. The latter two systems are retractable, allowing for a thinner vessel profile when docking, and reducing drag while cruising. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Stabilizer (ship)」の詳細全文を読む スポンサード リンク
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