page_title: Anti-rolling gyro
hierarchical_section_title: Anti-rolling gyro
caption_attribution_description: English: Two enormous gyroscopes being installed in the USS Henderson as a roll stabilizing system during its construction April 1917 at the Philadelphia Navy Yard in World War 1. The Henderson, a transport of 80 ton displacement, was the first large ship to be gyroscopically stabilized to prevent the ship from rolling from side to side with ocean swells. The gyros, built by Sperry Rand, consist of two 25 ton, 9 ft diameter flywheels which during operation are spun at 1100 RPM in opposite directions by 75 HP AC electric motors. Each gyro case is mounted on a vertical bearing which can be turned by a 75 HP servo motor. When a small sensor gyro on the ship's bridge sensed the ship roll, it ordered the servo motor to rotate the gyros about the vertical axis in a direction so the gyro's precession would oppose the ship's roll. During trials they were able to keep the ship roll down to 3 degrees in the roughest seas. This technology was replaced by roll stabilizer fins and is not used today.
context_page_description: Ship stabilizing gyroscopes are a technology developed in the 19th century and early 20th century and used to stabilize roll motions in ocean-going ships. Their function is similar to control moment gyroscopes or reaction wheels in spacecraft - they provide rotational stability via production of torque. It lost favor in this application to hydrodynamic roll stabilizer fins because of reduced cost and weight. However, since the 1990s, there is renewed interest in the device for low-speed roll stabilization of vessels. Unlike traditional fins, the gyroscope does not rely on the forward speed of the ship to generate a roll stabilizing moment and therefore can stabilize motor yachts while at anchor. However, the latest generation of "zero speed" fins stabilizers can stabilize yachts while at anchor thanks to their eccentricity with respect of the shaft.
  The World War I transport USS Henderson, completed in 1917, was the first large ship with gyro stabilizers. 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.
context_section_description: Ship stabilizing gyroscopes are a technology developed in the 19th century and early 20th century and used to stabilize roll motions in ocean-going ships. Their function is similar to control moment gyroscopes or reaction wheels in spacecraft - they provide rotational stability via production of torque. It lost favor in this application to hydrodynamic roll stabilizer fins because of reduced cost and weight. However, since the 1990s, there is renewed interest in the device for low-speed roll stabilization of vessels (Seakeeper, Quick MC2, etc.). Unlike traditional fins, the gyroscope does not rely on the forward speed of the ship to generate a roll stabilizing moment and therefore can stabilize motor yachts while at anchor. However, the latest generation of "zero speed" fins stabilizers (CMC, Humphree, etc.) can stabilize yachts while at anchor thanks to their eccentricity with respect of the shaft.
  The World War I transport USS Henderson, completed in 1917, was the first large ship with gyro stabilizers. It had two 25-ton, 9-foot (2.7 m) diameter flywheels mounted near the center of the ship, spun at 1100 rpm by 75 hp (56 kW) 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.
  The ship gyroscopic stabilizer typically operates by constraining the gyroscope's roll axis and allowing it to "precess" either in the pitch or the yaw axes. Allowing it to precess as the ship rolls causes its spinning rotor to generate a counteracting roll stabilizing moment to that generated by the waves on the ship's hull. Its ability to effectively do this is dependent on a range of factors that include its size, weight, and angular momentum. It is also affected by the roll period of the ship. Effective ship installations require rotors having a weight of approximately 3% to 5% of a vessel's displacement.
  Unlike hydrodynamic roll stabilizing fins, the ship gyroscopic stabilizer can only produce a limited roll stabilizing moment that may be exceeded as the wave height increases. Otherwise, it is not unusual for the manufacturer to recommend that the unit not be used at sea in large waves.
caption: Two 25-ton roll-stabilizing gyroscopes being installed on the transport USS Henderson during construction in 1917, the first large ship to use gyroscopic stabilization
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