This yacht went down in 8 feet of water. Unfortunately, the ocean currents on the reef where she came to rest were too much for her. She disintegrated within two weeks, with no chance of salvage.
This yacht was made of ferrocement, which defies logic about it's ability to float. Most people think of cement as what they use to weigh down pylons, not skin boats. Yet the physics apply with cement as much as they do fiberglass, steel and aluminum. A vessel needs only contain more buoyant forces than gravitational forces and it will remain above the waves.
Once the forces of gravity exceed the forces of buoyancy, the boat sinks. When water breaches the hull the battle with gravity begins in earnest, as water displaces the buoyancy.