John Baxter, of Doyle Midwest in Chicago, says these software tools are best used with customers to show how the shape evolves from when new—an example is shown belowfor the genoa on a new and a three-year-old Beneteau 36.7, which got a lot of heavy use throughout the season as the only class-legal sail.

“This sail was used for every race, Wednesday nights, and practice over that time,” says Baxter. “It probably has more than 500 hours on it, and was the only genoa the boat had.”

Part of determining when and what to replace will depend on a boat’s particular budget and its needs. “The genoa and other upwind headsails are the most abused sails of a boat’s inventory,” says Baxter. “They are flogged, bashed into the mast, pushed out of their intended wind range, crunched up on the foredeck, stepped on, and sometimes even dropped overboard. This constant abuse inevitably leads to a change in sail shape. In the new era of membrane-type sails this shape change is sometimes not as noticeable [as Dacron sails] because the sails remain smooth.”