Jackstay

Personnel transfer from USS Rankin by highline, a form of jackstay, 1960.

A jackstay is a cable or bar between two points to support and guide a load between those points, or as an anchor to attach something to be constrained along that line. The term is mostly used in a marine context and originated on sailing ships. Note the use of the term 'stay' implies load bearing working rigging. In diving it is also a line to guide the movements of a diver between the endpoints.