A disconnectable mooring system for a vessel comprises a mooring buoy member (2) and a turret structure (3), mounted in a moonpool (4) of the vessel (1). The mooring buoy has a plurality of passages (6) each adapted to receive a riser (7). The turret structure has a receptacle for receiving the buoy member and locking means for locking the buoy member in the receptacle. The turret structure (3) accommodates a plurality of conduits to be connected to risers installed in passages of the buoy member and the turret structure is rotatably supported in the moonpool (4) of the vessel (1) by means of at least a bearing assembly (16) mounted above sea level. The turntable (21) is supported on the bearing assembly (16) in a manner allowing rotation with respect to the turret structure (3) to align the conduits with the risers (7) when the buoy member (2) is received and locked in the receptacle of the turret structure (3).