I think it would be pretty easy for the direct injected outboards and the fuel injected inboards to run E85. Definately not rocket science. Just need a cheap sensor to check fuel alcohol level, bigger injectors and additional fuel curves set up in the computer. It would also require a closed venting system for the fuel system to avoid water absorbtion.
The media has been blasting corn alcohol, but I saw a algea farm set up in Arizona that looked promising for alcohol production. If the scientists can figure out how to make alcohol out of any plant matter, I think we could achieve oil independence in a few years.