Bolt rope

They also occur on the edges of sails suspended from a spar, such as for gaff, square and lateen rigs.

[3] Bolt ropes were described as early as 1847, when Robert Kipping addressed "bolt-rope" attachment for a variety of sails, using sewing techniques appropriate to each, in his book, The Elements of Sailmaking.

He addressed the tradeoff between stiffness and flexibility to provide reinforcement without distorting the intended shape of the sail.

He emphasized the need for the bolt rope not to affect the degree of slack on the leech (trailing edge) of a sail.

He further emphasized that the rope must retain its original twist, as it is sewn in place, to avoid distorting the edge of the sail.

Sail detail at the tack (lower corner of the leading edge) of a mainsail , showing bolt ropes in the luff and foot. Bolt ropes may extend to other parts of a sail , as well.
Sail construction detail ( tack corner ), showing a metal bolt rope (2) in the luff and a fiber bolt rope (3) in the foot