<P> Until the 14th century, the lateen sail was employed primarily on the Mediterranean Sea, while the Atlantic and Baltic (and Indian Ocean) 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 larger ships in stormy weather, and with the development of the carrack, the lateen was restricted to the mizzen mast . In the late eighteenth century, the lateen was replaced in European ships by the driver or spanker . </P> <P> The lateen survived as a rigging choice for mainsails of small craft where local conditions were favorable . For instance, barge - like 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 in the 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 . The balancelle, a Mediterranean coasting and fishing boat of the 19th century, also used a single lateen sail . </P> <P> One of the disadvantages of the lateen in the modern form described below is the fact that it has a "bad tack". 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 . </P> <P> However, there are forms of the lateen rig, as in vela latina canaria, where the spar is changed from one side to the other when tacking . This way the rig doesn't suffer these airflow disruptions that come from the sail pushed against the mast . </P>

How did lateen sails improve navigation on the indian ocean