A watersail is a
sail hung below the
boom. It is used mostly on
gaff rig
Gaff rig is a sailing rig (configuration of sails, mast and stays) 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''. Because of the size and shap ...
boats for extra downwind performance when racing. Often a watersail will be improvised from an unused foresail. Its psychological effects may be more effective than its aerodynamic ones.
{{Sail Types
Sailing rigs and rigging