In nautical parlance, the draft or draught of a sail is a degree of curvature in a horizontal cross-section. Any sail experiences a force from the prevailing wind just because it impedes the air's passage. A sail with draft also functions as an airfoil when set at an angle slightly greater than the angle of the wind, producing lift which then propels.
The word "belly" is also used in reference to the draft of a sail (i.e. "More belly in the main sail.").
- Barrie Smith; Jeremy Evans; Pat Manley (5 August 2013). The Sailing Bible: The Complete Guide for All Sailors from Novice to Experienced Skipper. Bloomsbury Publishing. pp. 83–. ISBN 978-1-4729-0157-6.