Crews on naval ships will have an easier time loading and receiving cargo from other ships while at sea, thanks to development of the Large Vessel Interface Lift On/Lift Off Crane at the Office of Naval Research. The motion-compensating crane delivers fully loaded cargo containers between ships at sea using computer control over its six degrees of freedom, and it can do so despite winds up to 20 knots and waves up to 7.5 ft (Sea State 4).
The crane is outfitted with a suite of sensors that detect the position and motion of the crane, the ship it’s mounted on, and the payload. An eccentric arm attaches to the ship and a boom then extends out to support an eight-wire inverted Stewart platform. A pair of wires attaches to each of the upper corners of a standard 20-ft ISO container. Relative motion between the ships, as well as the container, are damped out by computer-controlled motion of the eccentric arm and boom and the inherent stabilizing tendencies of the inverted Stewart platform.
In tests, the crane successfully picked up and moved containers between ships in the Gulf of Mexico, and even lowered them into holes, despite obstructed views on the part of the crane operator and waves up to 3-ft high. If deployed on ships, the crane could move cargo containers between ships at sea, a task now only possible when ships are in deep-water ports. It would also reduce the number of sailors needed to operate a shipborne crane from 10 to three.