As I understand it, rotomolded polyethylene has a density of 0.93 g/cc. Fresh water is 1.00 g/cc. Saltwater is about 1.02 g/cc. Without any hardware on an Adventure hull, it should float, especially in saltwater. Now, the hardware may add to the average density, and it may sink, but I doubt it would in saltwater. In any case, it would not need much floatation to float. The amas, for sure, would keep it above water.
When I first got my used 2011 AI, the lines immediately snagged a piece of floatation material and the block literally popped out of its location. After that, I removed some, but not all floatation--I didn't want the lines getting caught up with the floatation. With dry bags and boxes in the hull, the AI should float if swamped. I know mine did when I swamped it (operator error) on a camping trip. You can read about that at
http://www.hobiecat.com/forums/viewtopic.php?f=70&t=7276&start=180 Chokoloskee to Flamingo, Jan 16-23, 2012 An Inauspicious Beginning: One Sunken AI, One Empty Bottle of ScotchKeith