I think you're looking for the word "keel". It is located at the center of the hull bottom, below the waterline.
Dory
punt scow
ferry boat
shoal
gondola
A dory is one such boat.
A Dingy
Vessel
Bow, bulwark and bilge are sections of a boat. They begin with the letter b.
Boat...a gravy boat
A yacht.
Kelp - N/A Keel - Bottom on a boat