Ship stabilising gyroscopes are a technology developed in the 19th century and early 20th century and used to stabilise roll motions in ocean-going ships. It lost favour in this application to hydrodynamic roll stabiliser fins because of reduced cost and weight. However, more recently (since the 1990s) a growing interest in the device has reemerged for low speed roll stabilisation of vessels. The gyroscope does not rely on the forward speed of the ship to generate a roll stabilising moment and therefore has shown to be attractive to motor yacht owners for use whilst at an anchorage.
One of the most famous ships to first use a anti-rolling gyro was the 1930 Italian passenger liner the SS Conte di Savoia which had three huge gyros to control roll.
Gyroscopic roll stabilisers that use a passively damped (braked) precession motion in their designs have been marketed and produced by Mitsubishi and the Ferretti Group that have rotor moments of up to 15000 Nm.
Gyroscopic roll stabilisers with an actively damped (braked) precession motion have been developed by Seakeeper with rotor moments of 7000 Nm, suitable for boats and yachts under 100 feet.
Ship gyroscopic roll stabilisers that adopt both driven and damped (braked) actively controlled precession have been developed by Ship Dynamics with rotor momentums of 20 to over 2900 kNms, suitable for motor yachts and commercial vessels over 18 metres (60 feet).
The ship gyroscopic stabiliser 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 stabilising 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 approximately 3% to 5% of a vessel's displacement.
Unlike hydrodynamic roll stabilising fins, the ship gyroscopic stabiliser can only produce a limited roll stabilising moment that may be exceeded as the wave height increases. Otherwise, it is not unusual for the manufacture to recommend that the unit not be used at sea in large waves.