I think it's called a skeg.......does that help?
Also called a box keel it in the form of a box to allow pipes and other services throughout the keel length
A keel
The keel .
keel
keel
keel
the keel
A keel
it is called keel
The very bottom of a ship is where you find the keel. The keel runs the full length of the ship along its centerline and is the backbone of the hull. From the keel all the frames run out and up. the hull is attached to the frames. Picture the keel as the backbone and the frames as the ribs. The hull is the watertight skin that allows the ship to float. Within the hull are compartments (rooms) and at the top of the hull is the main deck. The superstructure is built upon the main deck.
The bottom of a car