The foam in the AS line is what makes them unsinkable. Technically, any relatively modern boat is unsinkable, as the USCG makes the manufacturer test (really, an actual test) smaller boats with full capacity load, to not sink when flooded with water. Obviously this test does not apply to larger vessels, like ships...
If you own an AS with a hull liner, the space between the liner and the hull will be filled with foam. If you have one without a hull liner, the space between the floor and the hull will be foam filled, sometimes with the area under the gunwales also foamed. Here's the catch - if the foam under the floor is waterlogged - well, I would guess Davy Jone's Locker has a couple AS boats...