The fin keel is a stationary foil positioned amidships and projecting downwards under the hull of a sailing vessel. A fin keel is relatively short in a fore-aft direction, and relatively deep, located near the center of the boat. A fin keel is a fixed element, unlike a
centerboard, which is retractable. The design purpose of the fin keel
[https://www.diva-portal.org/smash/get/diva2:737567/FULLTEXT01.pdf ] is to provide lateral resistance to wind forces applied to the boat via the sails and to facilitate the placement of ballast below the hull while presenting less wetted surface area than a full keel, which helps to reduce drag and leeway. The fin keel was invented by
James Brown Herreshoff (1834–1930).
References
Sailing vessel components
{{sailing-stub