A rope, bar, or batten placed along a ship's yard to bend the head of a square sail to.
- ‘Fuel transfer is accomplished by suspending a hose from a tensioned cable, the jackstay, which runs from RFA Fort Victoria to the receiving warship.’
- ‘During a stores transfer the jackstay supports a ‘traveller’, a travelling hoist to which loads of up to 2t may be coupled.’
- ‘All participating personnel were transferred to/from their respective ships, via light jackstay, RHIB or the Tobruk's embarked Sea King and Lynx helicopters.’
- ‘They conducted a comprehensive tour of the warship before observing the process of a light jackstay conducted with ANZAC.’