Gaff rig is a sailing rig (configuration of sails) in which the sail is four-cornered, fore-and-aft rigged, controlled at its peak and, usually, its entire head by a spar (pole) called the gaff. The gaff enables a fore and aft sail to be four sided, rather than triangular, and as much as doubles the sail area that can be carried by that mast and boom (if a boom is used in the particular rig). Additionally, for any given area of sail, the gaff rig will have a lower heeling moment than a triangular sail.
A sail hoisted from a gaff is called a gaffrigged sail.
Gaff rig remains the most popular rig for schooner and barquentine mainsails and other course sails, and spanker sails on a square rigged vessel are always gaff rigged. On other rigs, particularly the sloop, ketch and yawl, gaff rigged sails were once common but have now been largely replaced by the Bermuda rig sail, which, in addition to being simpler than the gaff rig, usually allows boats to sail closer to the direction the wind is coming from.
On larger gaff rigged vessels the gaff is hoisted by two halyards:
- The throat halyard lifts the end closer to the mast and bears the main weight of the sail and the tension of the luff.
- The peak halyard lifts the end further from the mast, and bears the leech tension.
Gunter-rigged boats are similar, smaller vessels on which the gaff is raised by a single halyard running on a wire gunter. On these rigs the gaff may be very nearly vertical and a topsail is never carried. Another variation is a gaff with no halyard. One end of the spar is attached to the peak of the sail and the gaff is hoist until it tensions the head and leach and then the other end is secured to the mast near the tack with a Snotter and are called Spritsails. This is considered a totally different rig.