The triangular lateen sail won out by being cheaper, not faster
Maritime historians long assumed the triangular lateen sail beat the old square sail at performance. Studies of voyages described in period accounts, and trials with replica ships, show the two performed about the same. The lateen spread across the Mediterranean from around the 5th century because it needed fewer costly fittings and was cheaper to build and maintain.
Lateen rigs first appear in the Mediterranean by roughly the 2nd century CE. At about the time they caught on, square rigs there were also being simplified, and both changes look like ways of cutting the price of fitting out a ship. On later three-masted ships the lateen served mostly as a balancing sail on the rear mast, useful for certain manoeuvres rather than for driving power. Paintings of 16th and 17th century ships often show it furled, and sailors on a replica of the Dutch ship Duyfken confirmed that limited role.
No one knows when the sail itself was invented, though some rank it with the wheel in importance. Pottery of the Cucuteni–Trypillian culture points to sailing boats from the 6th millennium BCE, and Mesopotamian digs from the Ubaid period give direct evidence. Egypt had a natural training ground: the Nile flows north while the prevailing wind blows south, so a boat could drift downstream and sail back up. Egyptian images of reed boats under sail date to around 3200 BCE.
Austronesian sailors took the idea furthest. Their words for sail go back to about 3000 BCE, when their Pacific expansion began. Their rigs held sails between spars along both the top and bottom edges, and they wove sails from salt-resistant pandan leaves. With the crab claw sail, outriggers and catamarans, they spread from Taiwan to Madagascar and Polynesia, settling lands across half the globe. Because single-outrigger craft became unstable when the outrigger ended up downwind, Pacific sailors reversed direction instead of turning, a technique called shunting.
A sail pushes through lift and drag. Angled into the apparent wind, it works like a wing; running downwind, drag does most of the work. Most displacement sailboats get their power from lift between roughly 40 and 135 degrees off the wind.
Source: Sail
