a locking and release mechanism for securing a loading / unloading buoy to a vessel . the buoy is of a type to be introduced into a submerged downwardly open receiving space in the vessel and to be fastened in a releasable manner in the receiving space . the locking and release mechanism includes hydraulically actuated locking elements mounted about horizontal axes at the sides of the receiving space to pivot between the locking and releasing positions . the buoy has a peripheral collar with downwardly facing abutment edge for engagement with the locking elements in the locking position thereof .