Nautical stabilizers, also known as keels, are a type of underwater fin that is attached to the bottom of a boat or SHIP. They provide stability and help to reduce rolling and pitching motions in rough seas. Keels are typically made of metal or fiberglass and can be either fixed or retractable. The term 'KEEL' comes from the Old English word for 'SHIP, ' and it is still used today to refer to the main structural element of a vessel.