Shape is typically built into sails using a combination of luff curve and broadseaming as is appropriate to the stability of the selected cloth. Modern very stable cloth works best with the shape essentially all produced by panel shaping (formerly broadseaming), and the luff curve cut to match mast bend (mains) or forestay sag (jibs). This approach requires sophisticated goemetry, but results in sails that are remarkably easy to trim and tune compared to those of other makers.
One-design racing sails are constructed for Thistles, Lightnings, Comets, Jet-14s, DaySailors, Snipes, Flying Scots, Buccaneers and most other racing classes. The design algorithm achieves maximum lift at all heights of the sail without flow separation. Compatibility between jib and main assures maximum performance for each sail. Highly stable cloths assure shape retention. Spinnakers reach at very small apparent wind angles, yet project maximum area downwind. Stability is assured through the use of geodesic (shortest distance) leeches.
Sails for traditional rigs are built with proper broadseaming to achieve good performance. This approach results in easier and safer boat handling than was achieved with the simpler cuts of yore.
Cruising designs use similar fast shapes as the racing sails. The optimum lift-to-drag ratios result in comfortable sailing because the heeling moment is reduced and weather helm is kept within the proper range. Cloths are selected for the appropriate combination of shape retention, handling and durability.