Your smart enough to figure out that a barge bigger then a football field can withstand the forces of rolling seas and mighty tidal waves alot better than a cube.
You should be smart enough to understand the stress on the keel as a barge hogs a swell.
Hogging and sagging - Wikipedia
A wooden keel is not able to handle these stresses in larger boats. Hogging and sagging can snap steel keels in larger vessels.