A brig is a sailing ship with two square-rigged masts. During the Age of Sail, brigs were seen as fast and maneuverable. They were used as both naval warships and merchant vessels. Even after the sailing age ended they were used as training ships. The brig was one of the smaller two-masted sailing ships. They popular in the 18th and early 19th centuries. Brigs fell out of use with the arrival of the steam ship because they required a relatively large crew for their small size. They were also difficult to sail into the wind.  They are not to be confused with a brigantine, which has different rigging (a brigantine has a gaff-rigged mainsail, while a brig has a square mainsail with an additional gaff-rigged spanker behind the mainsail). A brig is different from a three-masted ship because it only has two masts.

Rigging
In sailing, a full-rigged brig is a vessel with two square rigged masts (called the fore and main). The main mast of a brig is the aft (rear) one. To improve maneuverability, the mainmast carries a small (gaff rigged) fore-and-aft sail.
  
Brig sails are named after the masts to which they are attached. Those attached to the main mast are called the mainsail; above that the main topsail and above that the main topgallant sail. Occasionally a very small sail, called the royal, is above that. Behind the mainsail there is a small fore-and-aft sail called the spanker or boom mainsail (it is similar to the main sail of a schooner). On the foremast is a similar sail, called the trysail. Attached to the respective yards of square-rigged ships are smaller spars. These can be extended, which lengthens the yard. This allows it to receive an additional sailing wing on each side. These are called studding sails. They are used with fair and light wind only. The wings are named after the sails to which they are fastened. For example, the main studding sails, main top studding sails, and the main top gallant studding sails, etc.

The brig’s foremast is smaller than the main mast. The fore mast holds a foresail, fore topsail, fore top gallant sail, and fore royal. Between the fore mast and the bowsprit are the fore staysail, jib, and flying jib. All the yards are manipulated by a complicated arrangement of cordage named the running rigging. This is opposed to the standing rigging which is fixed, and keeps mast and other objects rigid. Traditionally the running rigging was easily recognized. This was because, for flexibility, it was not coated with tar and therefore of a lighter color. The standing rigging was tarred for protection from weather and therefore darker or even black in color.

Hull 
A brig is "generally built on a larger scale than a schooner. It could approach the size of a full-sized, three-masted ship." Brigs varried in length between 75 and 165 ft (23–50 m) with tonnages up to 480. Historically, most brigs were made of wood. However some later brigs were built with hulls and masts of steel or iron. Brigs with pine hulls were built in the 19th century. They was designed to last for about twenty years although many lasted longer.

Historic usage
Brigs were used as small warships carrying about 10 to 18 cannons. Due to their speed and maneuverability they were popular among pirates (though they were rare among American and Caribbean pirates). Their use stretches back before the 17th century. However one of the most famous periods for the brig was during the 19th century when they were involved in famous naval battles such as the Battle of Lake Erie. In the early 19th century the brig was a standard cargo ship. It was seen as "fast and well sailing", but required a large crew to handle its rigging. While brigs could not sail into the wind as easily as fore-and-aft–rigged vessels such as schooners a skilled brig captain could "manoeuvre it with ease and elegance; a brig could for instance turn around almost on the spot". A brig's square-rig also had the advantage over a fore-and-aft–rigged vessel when travelling in the open ocean. When fore-and aft rigged vessels sailed downwind for extended distances and where "the danger of a sudden jibe was the large schooner-captain's nightmare". This trait later led to the evolution of the barquentine. The need for large crews in relation to their smaller size led to the decline of the production of brigs. They were replaced in commercial traffic by gaff sail schooners (which needed smaller crews) and steam boats (which did not have the windward performance problems of square rigged ships).

The Telos, built in Bangor, Maine in 1883, was reportedly the last brig to join the American merchant marine. It was "considered to be the finest vessel of her class ever constructed in Maine".  She was wrecked on Aves Island, off Bonaire in the Caribbean, in 1900.

References 

Sailing
ships