Square rig

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Main-mast of a square-rigged ship, with all square sails set except the course.

A de-rigged square rigger in London.

Square rig is a generic type of sailing vessel in which the main horizontal spars are perpendicular to the keel of the ship. These spars are called yardarms or simply yards. Square rig was the main design in the age of sail.

Square rig can also describe individual four-cornered sails suspended from yardarms, and carried on either a square rigged or a mainly fore-and-aft rigged vessel, such as one with either a bermuda rigged or gaff rigged mainsail.

A mast is considered square rigged if its course is square rigged, but normally if this is the case it will have a complete set of square rigged sails. If the course is fore-and-aft, square topsails can still be carried in front of the mast.

Square rigged vessels range in size from small sloops to full rigged ships. However even for the largest vessels, the rig has been largely replaced by fore-and-aft gaff rigs and bermuda rigs. In the past, these more efficient rigs were impractical on larger vessels because of the loads that must be handled in hoisting and trimming the few large sails that are used. The square rig breaks up the sail area into many smaller sails, each of which can be individually handled by a manageable team hauling by hand on the lines. With the development of more advanced fittings and equipment, particularly geared winches, the load in an individual line became less of an issue, and the focus moved to minimising the number of lines and hence the size of the crew needed to handle them - a situation that favoured a few large sails instead of many small ones.

Similarly, hybrid vessels carrying some square-rigged sails have largely disappeared. The low aspect ratio of square rigged sails (usually 1/2 to 1/3) produce large amounts of drag for the lift they produce, and thus give very poor performance to windward. The Bermuda rig is the (nearly) undisputed champion of windward performance in soft sails, due to its very low drag and high lift to drag ratio. Square rigs do have their advantages, however; they are more efficient when running, where the high lift to drag is irrelevent and the total lift is the most important issue. Not only do square rigged sails provide better downwind performance, but they also are less prone to broaching when running than Bermuda rigs.

A square rigged sail is not in fact square, but more nearly trapezoidal, being symmetrical but longer in the foot than the head. Like all sails it is three-dimensional, and its curve or belly means its foot is not a straight line at all. It is fixed to a spar along its head, and its clews are controlled by sheets, often run to blocks on the spar immediately below the sail. The lower sails, without a spar below them, may also have tacks.

Modern square rigged ships are still used for training, tourism and ceremonial purposes.

Types of square rig

Principally square rigged types

A barque has three or more masts, with the aftermost entirely fore-and-aft rigged, while the fore, main and any others are square rigged.
A brig has two masts, both square rigged.
A full rigged ship has three or more masts, including a foremast, mainmast and mizzen, and all masts are square rigged.
A sloop has only one mast.

All the above rigs normally carry a number of jibs and at least one spanker, and may also carry fore-and-aft staysails between the masts.

Fore-and-aft rigs with some square rigged sails

A barquentine has three or more masts, the fore square rigged, the main, mizzen and any others fore-and-aft rigged.
A brigantine has two masts: A square rigged foremast and a fore-and-aft rigged mainmast.
A square-topsail ketch carries one or more square-rigged topsails (commonly two, an upper and a lower topsail) on its mainmast, in addition to its mainsail, mizzen sail and jibs.
A square-topsail schooner carries one or more square-rigged topsails on its foremast. This rig is often simply called a topsail schooner as topsails above the gaff-rigged sails are a standard part of the schooner rig.
A square-topsail cutter or sloop carries one or (less commonly) two square topsails on its only mast, in addition to its mainsail and jib or jibs.

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