Brig sails are named after the masts to which they are attached: the mainsail; above that the main topsail; above that the main topgallant sail; and occasionally a very small sail, called the royal, is above that. Behind the main sail there is a small fore-and-aft sail called the spanker or boom mainsail (it is somewhat similar to the main sail of a schooner). On the foremast is a similar sail, called the trysail.