A sail that no longer sets is still a triangle of very good cloth. Type its three sides — luff along the mast, leech the free edge, foot along the boom — and the biggest hammock that fits is drawn on it. Turn the sail to lay the hammock along another side; Best picks the side that gives the most.

The hammock is the body plus what sewing costs: a 4 cm hem all round and a 12 cm channel at each end, for a rope drawn through (gathered ends) or a spreader bar. What is left is counted out in 40 × 40 pillows and 30 × 40 bags, each with its own seam.

Why sailcloth. Woven Dacron does not stretch and takes a body without bagging; laminates are stiffer still. Both sit outdoors for years. The leech is the edge that saw the most sun — check it before you cut, and cut the hammock out of the middle if the edge is chalky.

What it cannot do. It does not know where your sail is worn, torn or stitched: the sail it draws is a clean triangle. It only cuts triangles — a four-sided sprit sail like an Optimist's is not in here. And not every sail will do: a spinnaker is ripstop nylon, far too light and it stretches; a stretchy or rotten cloth is a fall, not a hammock. The presets are rounded class sizes, real sails vary.