Sail-plan

A sail plan is a set of drawings, usually prepared by a naval architect which shows the various combinations of sail proposed for a sailing ship. Alternatively, as a term of art, it refers to the way such vessels are rigged as discussed below.

The combinations shown in a sail-plan almost always include three configurations:

In all sail plans, the architect attempts to balance the force of the sails against the drag of the underwater keel in such a way that the vessel naturally points into the wind. In this way, if control is lost, the vessel will avoid broaching (turning edge-to-the wind), and being beaten by breaking waves. Broaching always causes uncomfortable motion, and in a storm, the breaking waves can destroy a lightly built boat. The architect also tries to balance the wind force on each sail plan against a range of loads and ballast. The calculation assures that the sail will not knock the vessel sideways with its mast in the water, capsizing and perhaps sinking it.

Each form of rig requires its own type of sails. Among them are:

The standard terminology assumes three masts, from front to back, the foremast, mainmast and mizzenmast. On ships with fewer than three masts, the tallest is the mainmast. Ships with more masts number them.

From bottom to top, the sails of each mast are named by the mast and position on the mast, e.g. for the mainmast, from lowest to highest: main course, main topsail, main topgallant ("t'gallant"), main royal, main skysail, and main moonraker. Since the early nineteenth century, the topsails and topgallants are often split into a lower and an upper sail to allow them to be more easily handled. This makes the mast appear to have more "sails" than it officially has.

On many warships, sails above the fighting top (a platform just above the lowest sail) were mounted on separate masts ("topmasts" or "topgallant masts") held in wooden sockets called "tabernacles". These masts and their stays could be rigged or struck as the weather and tactical situation demanded.

...
Wikipedia