A lateen (from a la trina, meaning triangular) or latin-rig is a triangular sail set on a long yard mounted at an angle on the mast, and running in a fore-and-aft direction. In western culture, the rig is originally reported found on sailing ships about the Mediterranean Sea, where the sail plan may have originated with the Arab traders plying the coastal routes of the spice trade across the Red Sea and Indian Ocean. The lateen is used today in a slightly different form on small recreational boats like the highly popular Sunfish, but is still used as a working rig by coastal fishermen in the Mediterranean.
The origins of the lateen rig date back to the Roman fore-and-aft rig, which has been in use in the Mediterranean Sea since the 3rd century AD. The earliest evidence of lateen sails comes in form of several Greek and Roman reliefs and mosaics, dated between the 2nd and 4th century AD, showing both the triangular lateen and the so-called "Arab lateen" (better: Near Eastern lateen) to be fairly widespread already in late antique navigation. By the 6th century the lateen had replaced the square sail as standard rig on many Byzantines galleys in the Mediterranean, and was probably also employed by Belisarius' flag ship in the 532 AD invasion of the Vandal empire. In this light, the attribution of the lateen to the Arabs can no longer be upheld:
The evidence casts doubt not only on the attribution of the lateen sail to the Arabs, but also on the Arabs as the agents of its diffusion. The lateen sail can therefore no longer be described as an innovation that Europe owes to the Arabs. On the contrary, the lateen in the Mediterranean had a continuous history of more than 1,500 years before it was adapted to the needs of Atlantic exploration by the Portuguese.Until the 14th century, the lateen sail was employed primarily on the Mediterranean Sea and Indian Ocean, while the Atlantic and Baltic vessels relied on square sails. The Northern European adoption of the lateen in the Late Middle Ages was a specialized sail that was one of the technological developments in shipbuilding that made ships more maneuverable, thus, in the historian's traditional progression, permitting merchants to sail out of the Mediterranean and into the Atlantic Ocean; caravels typically mounted three or more lateens. However, the great size of the lateen yardarm makes it difficult and dangerous to handle on large ships in stormy weather, and by the eighteenth century the lateen was restricted to the mizzen mast. In the early nineteenth century the lateen was replaced in European ships by the driver or spanker.
However, the lateen survived as a rigging choice for mainsails of small craft where local conditions were favorable. For instance, bargelike vessels in the American maritimes north of Boston, called gundalows, carried lateen rigs throughout the late nineteenth and early twentieth centuries. Likewise, lateen sail survived at Baltic until the late 19th century. Because the yard pivots on its point of attachment to the mast, the entire sail and yard can be swiftly dropped. This was an advantage when navigating the tidal riverways of the region, which often required passage under bridges.
One of the disadvantages of the lateen, especially in the modern form described below, is the fact that it has a "bad tack". Since the sail is to the side of the mast, on one tack that puts the mast directly against the sail on the leeward side, where it can significantly interfere with the airflow over the sail. On the other tack the sail is pushed away from the mast, greatly reducing the interference. On modern lateens, with their typically shallower angles, this tends to disrupt the airflow over a larger area of the sail.
The lateen rig was also the ancestor of the Bermuda rig, by way of the Dutch bezaan rig. In the 16th Century, when Spain ruled the Netherlands, Moorish lateen rigs were introduced to Dutch boat builders who soon modified the design by omitting the mast and fastening the lower end of the yard directly to the deck, the yard becoming a raked mast with a full-length, triangular (leg-of-mutton) mainsail aft. Introduced to Bermuda early in the 17th Century, this developed into the Bermuda rig, which, in the 20th Century, was adopted almost universally for small sailing vessels.
The lateen sail was used in Arabian Seas at least since the fourth century B.C.
The modern lateen differs from traditional lateens by the addition of a spar along the foot of the sail, similar to the crab claw sail traditionally used on the proa. The lower spar is horizontal, and is attached to the mast where it crosses. The front ends of both spars are joined together. Both joints are designed to allow free rotation in all directions. The sheet is attached to the lower spar, and the halyard to the upper spar. The geometry of the sail is such that the upper and lower spars are confined to a plane parallel to the mast. This results in the sail forming a conic section, identical to half of the Rogallo wing commonly found in kites and hang gliders.
The modern lateen is often used as a simple rig for catboats and other small recreational sailing craft. In its most basic form, it requires only two lines, a halyard and a sheet, making it very simple to operate. Often, additional lines are used to pull down the lower spar and provide tension along the upper and lower spars, providing greater control over the sail shape.
Since the upper and lower spars provide a frame for the sail, the camber of the sail is simply a function of how tightly the spars stretch the sail. This means that lateen sails are often cut flat, without the complex cutting and stitching required to provide camber in Bermuda rig sails. Curved edges, when mated with the straight spars, provide all or nearly all of the sail curvature needed.