Sail

Sails may be made from a combination of woven materials—including canvas or polyester cloth, laminated membranes or bonded filaments, usually in a three- or four-sided shape.

[4]: 173 Much of the early development of water transport is believed to have occurred in two main "nursery" areas of the world: Island Southeast Asia and the Mediterranean region.

[4]: 174, 175 Archaeological studies of the Cucuteni-Trypillian culture ceramics show use of sailing boats from the sixth millennium BCE onwards.

Ancient Sumerians used square rigged sailing boats at about the same time, and it is believed they established sea trading routes as far away as the Indus valley.

They did not become common until the 5th century, when there is evidence that the Mediterranean square sail (which had been in wide use throughout the classical period) was undergoing a simplification of its rigging components.

[b] Both the increasing popularity of the lateen and the changes to the contemporary square rig are suggested to be cost saving measures, reducing the number of expensive components needed to fit out a ship.

[13] It has been a common and erroneous presumption among maritime historians that lateen had significantly better sailing performance than the square rig of the same period.

Analysis of voyages described in contemporary accounts and also in various replica vessels demonstrates that the performance of square rig and lateen were very similar.

[14][13] The lateen was adopted by Arab seafarers (usually in the sub-type: the settee sail), but the date is uncertain, with no firm evidence for their use in the Western Indian Ocean before 1500 CE.

There is, however, good iconographic evidence of square sails being used by Arab, Persian and Indian ships in this region in, for instance, 1519.

[15] The popularity of the caravel in Northern European waters from about 1440 made lateen sails familiar in this part of the world.

It did not, however, provide much of the propulsive force of these vessels – rather serving as a balancing sail that was needed for some manoeuvres in some sea and wind conditions.

The extensive amount of contemporary maritime art showing the lateen mizzen on 16th and 17th century ships often has the sail furled.

[19][20] The proto-Austronesian words for sail, lay(r), and some other rigging parts date to about 3000 BCE when this group began their Pacific expansion.

[22][23] Crab claw sails used with single-outrigger ships in Micronesia, Island Melanesia, Polynesia, and Madagascar were intrinsically unstable when tacking leeward.

To deal with this, Austronesians in these regions developed the shunting technique in sailing, in conjunction with uniquely reversible single-outriggers.

In the rest of Austronesia, crab claw sails were mainly for double-outrigger (trimarans) and double-hulled (catamarans) boats, which remained stable even leeward.

For apparent wind angles behind the sail, lift diminishes and drag increases as the predominant component of propulsion.

[48][39] Woven materials, like Dacron, may specified as either high or low tenacity, as indicated, in part by their denier count (a unit of measure for the linear mass density of fibers).

Mainsails are more likely to be bi-radial, since there is very little stress at the tack, whereas head sails (spinnakers and jibs) are more likely to be tri-radial, because they are tensioned at their corners.

[48] Higher performance sails may be laminated, constructed directly from multiple plies of filaments, fibers, taffetas, and films, instead of woven textiles that are adhered together.