Gyrostabilisers

A gyrostabiliser including a vacuum chamber assembly comprising:

• a flywheel enclosed within a vacuum chamber formed by a housing;
• a flywheel shaft fixed to or integral with the flywheel and located relative to the housing by upper and lower spin bearings which permit rotation of the flywheel about the spin axis, wherein the vacuum chamber assembly further comprises:
• an upper spin bearing chamber and an upper shaft seal around the flywheel shaft, the upper spin bearing chamber accommodating the upper spin bearing, and being separated from the vacuum chamber by the upper shaft seal, allowing the upper spin bearing chamber to be maintained at a different pressure to the vacuum chamber,
• a lower spin bearing chamber and a lower shaft seal around the flywheel shaft, the lower spin bearing chamber accommodating the lower spin bearing, and being separated from the vacuum chamber by the lower shaft seal, and
• wherein the gyrostabiliser comprises an oil circuit having at least one outlet into the upper spin bearing chamber, at least one drain out of the upper spin bearing chamber, at least one outlet into the lower spin bearing chamber and at least one drain out of the lower spin bearing chamber.