Restricted in ability to manoeuvre (RAM)

A vessel restricted in her ability to maneuver is one which from the nature of her work cannot keep out of the way as required by the rules: examples in Rule 3(g) include laying or servicing a navigation mark, dredging, surveying or underwater operations, replenishment at sea, launching or recovering aircraft, and a towing operation that severely restricts the tow and tug. By day she exhibits ball-diamond-ball shapes in a vertical line, and by night three all-round lights red-white-red. She ranks above a power-driven vessel and a sailing vessel in the Rule 18 hierarchy.