A system (10) for coupling first and second vessels (12,14) to minimize movement therebetween while allowing for lightering. The system (10) comprises rams (20,22) and coupling heads (36,38) associated with the first vessel (12), and receivers (24,26) associated with the second vessel (14) for receiving the coupling heads (36,38). The system (1) allows for at least three configurations: a first configuration in which the rams (20,22) are extended and the coupling heads (36,38) are rotated such that first faces (42) interlock with the receivers (24,26); a second configuration in which the rams (20,22) are extended and the coupling heads (36,38) are rotated such that second faces (44) abut the receivers (24,26); and a third configuration in which the rams (20,22) are retracted such that the coupling heads (36,38) do not interact with the receivers (24,26). Lightering is accomplished by a series of short-duration switches between the second and third configurations.