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keel2 Eastern English dialect
(1) Keel of a vessel—a longitudinal, usually composite, beam running in the middle of the vessel bottom from the bow to the stern. The keel serves as a basic longitudinal link providing strength and rigidity to the bottom and overall stability to the vessel’s hull.
Wooden vessels have a keel in the form of a bar; this form was also retained on old metal-hull vessels (bar keel). On modern double-bottomed steel vessels the keel consists of a thick reinforced plate on the bottom and one or two (duct keel) vertical plates located between the double bottom. Bilge keels (side keels) in the form of long rigid plates are installed along what is called the turn of the bilge on the outside of the hull in order to lessen the rolling of the vessel.
(2) Keel of an airship—fin or vertical stabilizer—part of the tail unit of an aircraft located in a vertical (or inclined) plane and designed to provide directional stability. A flight rudder is attached by hinges to the trailing edge of the fin.