From the Nautical Dictionary...
“The pumps of a vessel are sometimes worked by
means of a contrivance called the vangee, or weegee, or wheejee; this usually consists of a barrel of an octagonal form turning back-wards and forwards on a pivot fixed in a frame between the pumps; the pump-spears are attached by arms to this barrel, and the pumps are worked by two brakes inserted into it at right angles to each other, with ropes attached to their ends for hauling upon”.
From personal experience, on a modern sailing yacht the ‘vang’ is a rope that applies downward force to the boom, more commonly known as a ‘kicker’ in smaller sailing boats. And I now wonder if vang derives from vangee? Vang in this usage is in Chambers...