Anti rolling gyro
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Ship stabilising gyroscope is a technology developed in the 1800s and early 1900s and used to stabilise roll motions in ocean going ships. It lost favour in this application in favour 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 forward-speed roll stabilisation of vessels. The gyroscope does not rely on the forward speed of the ship to generated a roll stabilising moment and therefore has shown to be attractive to motor yacht owners for use whilst at an anchorage.
Recent gyroscopic roll stabilisers that use a passive precession motion in their designs have been marketed and produced by Mitsubishi and the Ferretti Group that have rotor momentums of up to 15 kNms.
Ship gyroscopic roll stabilisers that adopt an active precession in their design have been developed and produced by Ship Dynamics with rotor momentums of over 500 kNms.
The ship gyroscopic stabiliser typically operates by contraining 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 dependant 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 1% to 3% 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 unless large wave height forces are factored into its design. Otherwise, it is not unusual for the manufacture to recommend that the unit not be used at sea in large waves.
