JACKSTAY

A stay (rope, bar or batten), running along a ship's yard, to which is attached the head of a square sail.

A cable between two ships or from a ship to a fixed point which can be used to support a load during transfer of personnel or materiel along the cable.

A line (rope, webbing or cable), attached to a boat at the ends, to which a safety harness can be clipped to restrain falling in rough conditions and to prevent falling overboard.