dock
Dory
I think you're looking for the word "keel". It is located at the center of the hull bottom, below the waterline.
Boat...a gravy boat
A mesa has a flat top.
Ship?
'Flat' is one...
keel
flat
the men were all married
plat
Flat, even.
A square box - with top and bottom both square. (or a box with square ends)The top and bottom make two squares, the four other sides are flat and rectangular. There are eight corners - four around the top and four around the bottom. There are twelve edges, four around the top, four around the bottom, and four joining the top and bottom.A rectangular box is also called a rectangular parallelepiped.