Abstract: A buoy for use in loading or unloading a flowable medium, especially oil from a vessel at sea. The buoy includes an outer buoyancy member having a conical shape, and a central member, rotatably mounted in the outer member which forms a passage for the flowable medium from the lower end of the buoy which is connected to a transfer line to a delivery system within the vessel. The outer member is received and locked in a conical shaped opening in the bottom of the vessel which is connected to a receiving space which extends up to the deck of the vessel. The outer member forms a seal with the lower end of the opening to seal the sea off from the receiving space. The central member, has a relatively small mass and a small inertia, such that the outer buoyancy member together with the vessel may readily turn thereabout.