A device for installation in a floating vessel which is intended for receiving a buoy or a turret in a submerged receiving space at the bottom of the vessel. The device comprises a tubular body (5) dimensioned for installation in a shaft (2) extending vertically through the hull of the vessel and which, at its lower end, is arranged to receive a module unit (6) provided with a through opening (8) for receiving the buoy/turret. When the module unit (6) is installed in the tubular body (5), the module unit at its lower end forms a seal (37) against the tubular body (5), and at its upper end the module unit (6) is fixed in relation to the tubular body (5) by locking means (40).