1. Function

2. History

3. See also

4. References

Ship stabilizers (or stabilisers) 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 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, each installed underwater on either side of the ship, are used. Stabilizers can be:

• Retractable - All medium and large cruise and ferry ships{{citation needed|date=September 2018}} have the ability to retract the fins into a space inside the hull in order to avoid extra fuel consumption and reduce the required hull clearance 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.^[1] Stabilization solutions at anchor or at low speed include actively controlled fins (such as the stabilisation at rest system developed by Rolls Royce^[2] 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.

History

One early stabilization technology is the anti-rolling gyro, or gyroscopic stabilization. The World War I transport USS Henderson, completed in 1917, was the first large ship with gyro stabilizers (right). It had two 25-ton, 9-foot diameter flywheels mounted near the center of the ship, spun at 1100 RPM by 75 HP AC motors. The gyroscopes' cases were mounted on vertical bearings. When a small sensor gyroscope on the bridge sensed a roll, a servomotor would rotate the gyros about a vertical axis in a direction so their precession would counteract the roll. In tests this system was able to reduce roll to 3 degrees in the roughest seas. One of the most famous ships to first use an anti-rolling gyro was the Italian passenger liner {{SS|Conte di Savoia}}, which first sailed in November 1932. It had three flywheels which were 13 feet in diameter and weighed 108 tons.^[3] Gyroscope stabilization was replaced by fin stabilization due to its lower weight and bulk, but it has seen renewed interest since the 1990s (Seakeeper, etc.).{{CN|date=September 2018}}

The passive bilge keel is an early 20th-century stabilizing innovation, not as effective at reducing roll, but easier to install, and does not require space inside the hull.{{citation needed|date=September 2018}}

The first mention of automatic fin stabilizers for ships was in 1932 by an engineer working for General Electric.^[4]

The first use of fin stabilizers on a ship was by a Japanese cruise liner in 1933.^[5]

In 1934 a Dutch liner introduced one of the world's most unusual ship stabilizer systems, in which two large tubes were mounted on each side of the ship's hull with the bottom of the tubes open to the sea. The top of the tubes had compressed air or steam pumped in. As the ship rolled, the side it was rolling to would fill with water and then compressed air or steam would be injected to push the water down, countering the roll.^[6]

In the 2010s, Blue Origin was building a hydrodynamically stabilized ship as a moving floating landing platform in order to recover launch vehicle first stages to enable them to be refurbished and used again. Blue's New Glenn launch vehicle will launch from eastern Florida and be recovered downrange on a stabilized landing ship in the Atlantic Ocean.^[7]

See also

• Ship stability
• Stabilization while not under way

References

• Claiton Alberto Fontoura dos Santos
• Claiton (footballer, born 1978)
• Claiton (footballer, born 1984)
• Claiton Machado Santos
• CLAL
• Clalit Health Services
• Clallam Bay
• Clallam Bay Corrections Center
• Clallam Bay, WA
• Clallam Bay, Washington
• Clallam County (Washington)
• Clallam language
• Clallam Transit
• Clam Abuse
• Clam Anti Virus
• Clam Antivirus
• Clamator
• Clamator coromandus
• Clamator levaillantii
• ClamAv
• Clam AV
• ClamAV
• ClamAV Virus Database
• C. Lamb
• Clam bake