fin keel

noun, Nautical
1.
a finlike projection extending downward from the keel of a sailboat, serving to prevent lateral motion and acting as additional ballast.
Examples from the web for fin keel
  • The new cup-defender will be to all intents and purposes a big fin keel.
  • The fin keel is getting a heavy rubbing with soft emory cloth.
British Dictionary definitions for fin keel

fin keel

noun
1.
a projection from the keel of a vessel to give it additional stability