It’s just water displacement. Remember that water exerts increasing amounts of force as you go deeper—and rapidly so.
The most fascinating example if that of the aircraft carrier. When you look at it, you’d never guess that it would float.
The trick has to do with the weight at the bottom of the ship.
It is a giant weight that’s constantly trying to pull the boat down. But the displacement of water makes the ship float perfectly, causing this tension to stabilize the ship perfectly.
Think of a balloon with a weight tied to it. It might go down. It might go up. But it will never flip over. That subsurface protrusion was discovered in the 19th century as a way of drastically reducing drag on the ship.
Regardless, oceanic vessel engineering is highly underappreciated.