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.