What a lateen sail is
A lateen sail is a triangular sail attached to a long spar, called a yard, which is set at an angle on a short mast. The front edge of the sail is along the yard and the rear corner extends toward the stern. The word “lateen” is thought to derive from the French for “Latin”, reflecting its association with the Mediterranean, though the sail’s origins are broader than that name suggests.
Many ship types used it, from small Mediterranean fishing boats to the large Arab dhows that crossed the Indian Ocean. It also appeared on some European ships, including caravels, which were famous for their lateen rigs.
Why sailing into the wind is not possible, and what is
No sailing ship can move directly into the wind. What a sail can do is let a boat travel at an angle to the wind. A modern way to understand it is that a sail works somewhat like a wing: air flowing around the curved sail produces a force, partly pulling the boat sideways and partly forward, and the keel or hull shape resists the sideways motion. This is related to the principles of wing design in aircraft, although a sail is a much simpler shape.
A square sail hangs across the ship and works best with the wind behind or to the side. If a ship with square sails tries to head too close to the wind, the sails lose their shape or press back against the mast. Typical square-rigged ships could manage to sail to roughly 70 degrees or so from the wind direction, depending on the design, while a well-handled fore-and-aft rig can sometimes manage closer. These numbers vary a great deal with hull shape, sail cut and sea conditions, so they should be taken as rough ranges.
A lateen sail lies along the length of the ship, so it is a fore-and-aft sail. Because it can be trimmed flatter and set closer to the ship’s centerline, a lateen-rigged vessel can usually sail closer to the wind than one with a simple square sail. To make progress to windward, the crew zigzags in a series of legs, a method called tacking.
The awkward part: changing tack
The lateen has a drawback. The long yard sits on one side of the mast, and when the ship changes tack by turning its bow through the wind, the sail must be brought to the other side. On many vessels, this means swinging the long yard around the mast, a heavy job that needs a large crew. Some ships avoided turning through the wind altogether and instead turned away from it in a wide arc, called wearing, which costs distance. Large lateen yards could be very long, sometimes longer than the ship, and heavy to handle in a sea.
Even so, the rig had real advantages: it was relatively simple, worked well in light and moderate winds, and let small crews handle moderately sized ships.
Where it came from
The origin of the lateen sail is debated. Triangular sails appear in Mediterranean art in the late classical period, and many historians place the spread of the lateen rig in the Mediterranean in the first millennium CE, with Byzantine ships using it by the sixth century or so. Earlier evidence of fore-and-aft rigs in the Mediterranean exists, such as small spritsails, so the development was probably gradual. Some scholars suggest a connection with Indian Ocean traditions, while others favor Mediterranean development. The evidence is thin, and no single inventor or date can be reliably named.
Indian Ocean trade
The Indian Ocean is dominated by the monsoon, a seasonal wind pattern that blows from the southwest in summer and the northeast in winter. Sailors could use this regularity to travel one way and return months later when the wind reversed. Arab, Persian, Indian and East African traders used dhows and related ships for this exchange, carrying cargoes such as spices, textiles, timber and ivory. Some of these vessels had hulls sewn together with cord made of coconut fiber, which links back to rope making as a basic shipbuilding skill.
Because the monsoon often favors a broad reach rather than a hard beat to windward, lateen sails served the trade well. They also let ships handle the shifting coastal winds of the Red Sea and Arabian Sea.
Mediterranean use
In the Mediterranean, the lateen was used by galleys, which had oars as well, and by many merchant ships from the medieval period onward. In the later Middle Ages, lateen and square rigs were sometimes combined. Southern European ships of the fifteenth century are the best-known examples of mixed rigs, and these later helped lead to the multi-masted ships of the age of exploration. The caravel, with lateen sails on its early forms, is the most famous example.
Legacy
Square sails remained popular for long ocean voyages, but the lateen’s principle of a fore-and-aft sail that could be set close to the wind influenced later rigs, including the gaff and Bermuda sails. Lateen-rigged boats are still used today in parts of the Mediterranean, Red Sea and Indian Ocean, and the shape is also familiar on small recreational boats. It shows how a design that is awkward to tack can still be a practical answer for the winds and trades of a region.