There are multiple issues with ANY ethanol additive in a gasoline product.
First and foremost, ANY ethanol based fuel will require more fuel to be burned than straight gasoline due to the BTU rate of any alcohol being less than a traditional gasoline. Alcohol of any type generally burns at about 1/2 the temperature of gasoline, so to make the same amount of horsepower from an alcohol-based fuel(10% is generally what they mix ethanol with gasoline) it will take more of the mixed fuel to make the same temperature during the combustion cycle in your engine than it will a straight gasoline, regardless of octane(which once again, has nothing to due with temperature of the burn) to explain it simply as far as the burn temperature goes, it takes a large explosion in the cylinder to drive the pistons back down the bore. The larger and hotter the explosion, the faster the pistons are driven down(or the more force they are driven down with) and this is how power is made. Controlling the explosion is a rather interesting science and I could really get deep in to it but won’t do it here.
Secondly, as in any alcohol-based fuel, you have to have the proper fuel system to use that type of fuel. While it might seem insignificant, ethanol/alcohol will attack many older types of fuel lines and either cause leaks(under pressure) or the lines will start to fall apart internally and clog filters and/or carburetors and injectors for the fuel injected crowd. On a two-stroke, clogged fuel systems lead to lean fuel mixes, which lead to detonation or high cylinder temps....which burns/breaks pistons. If you haven’t burnt a piston in a two-stroke you’re in for a treat on that one!
Third and also important in marine use, the fact that ANY alcohol additive or mixture in fuel ALSO causes water to accumulate in your fuel. This is due to the condensation associated with the evaporative rate of alcohol. Any temperature inversion or difference will cause condensation to occur depending on dew point, temperature and pressure altitude(usually whatever sea-level is here) it varies from minute to minute with the sometimes drastic temp changes we get in thunderstorms, big north winds, etc. This water accumulation generally isn’t really harmful on something that is run daily/weekly. Here’s the catch, the separation can occur within hours, once again depending on temps and pressures. If this occurs through several weeks or months and you haven’t run your boat/car/motorcycle that water can accumulate in float bowls in your carbs(corrodes aluminum carbs at a very rapid rate) in filters, once again corrosion, and fuel injectors causing them to stick(open and closed) I’ve had this issue with my bike and one of my hotrods that sat for a few months. My car actually lost one whole side of the carb going down highway 29 and when I finally got it home, the carb was junk(irreparable) and it cost me a $400 carb. The car had been at a body shop in Jackson Ms. for about three months....that’s it.
In short, if you can stay away from an ethanol mixture you’ll be better in the long term. Between parts failures and fuel system upgrades you might save yourself a big wad of cash by not hunking a motor 25 miles off the beach(or in grande lagoon) run your motor weekly to keep fuel from sitting and getting stagnant, use a fuel stabilizer if possible because it doesn’t just stabilize fuel, it also lubes fuel system components and can help to condition rubber parts. Sorry for the length but I haven’t seen anyone actually try to take the time to explain this stuff...........and I had a few extra minutes after taking my old 69 Dart out for a ride tonight! Tomorrow, the 70 Camaro gets its first run in a month!