Jackstay  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 "stay" implies load bearing working rigging. In diving it is also a line to guide the movements of a diver between the endpoints. Jackstays are used in several maritime applications. These include:  A diving jackstay is a form of guideline laid between two points to guide the diver during a search or to and from the workplace or to support and guide equipment for transport between two points. A downline is a diving jackstay from an anchor point at or above the surface to the underwater workplace used to control descent, ascent and the transfer of tools, materials and other equipment between the surface and the workplace. Functions:  Images of jackstays.