Abstract: The invention relates to a gyrostabiliser assembly (1) for a marine vessel comprising: a housing (2) defining a chamber (3) for supporting at least a partial vacuum; a flywheel (4) mounted within the chamber (3) for rotation about a spin axis (Z) at the partial vacuum; a flywheel shaft (5) upon which the flywheel (4) is supported and mounted in the housing for rotation of the flywheel about the spin axis (Z), the flywheel shaft being rotatably supported by a first spin bearing (6) located at one end region of the shaft (5) and a second spin bearing (7) located at an opposite end region of the shaft (5); and a lubrication system (8) configured to circulate lubricant (O) to the spin bearings (6, 7) from a lubricant reservoir (9). The reservoir (9) is arranged in or on the housing (2) to collect lubricant from the spin bearings (6, 7) under gravity and the first and second spinbearings (6, 7) are arranged in the housing (2) for operation under the partial vacuum.