Jackline

is the other name by which Jackstays are known. Whichever you prefer, Jackstay or Jackline, both terms actually refer to any line rigged securely between two points and used as a support. Indeed, the names can correctly be used to refer to: the line from which a refuelling hose is suspended when RASing, the centre line used to support an awning rigged over a hot deck, a line rigged between ship and shore along which a breeches bout could be hauled, and a line rigged to a spar on a square-rigged ship to which the head of a sail is attached.

Importantly, given their use in situations where support is required, they should always be rigged with a minimum safety factor of four, i.e. the load supported by the Jackstay, including its own weight, should not be more than one-quarter the breaking strain of the wire or rope used.

(with thanks to 'The Oxford companion to Ships and the Sea' - perhaps the most beguiling book of all time)