Ok I called them. Product has only been available since Nov 2012.
Right now not recommended for something continually underwater as the treated surface may need to be recharged with air. She did say they have it on a steel
plate been underwater for 30 days and it is still working as designed.
Also sometime this summer, Rustoleum will be marketing
it to retail consumers.
So maybe when it is available to ordinary buyers, someone will test it for a boat bottom.
I think it could be a remarkable use if it did work on the bottom and only way to tell is to test.