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Vehicles with electronic timing will always perform better on Premium fuel, given several tank fulls to set adjustments to the timing and fuel maps.

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E15 is federally prohibited for recreational vessel use, according to the Coast Guard. It also can cause marine engine damage and void marine engine warranty.

Additionally, the fuel has reportedly been shown to make engines run hotter and increase the possibility of a boat fire.

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BoatUS notes recreational vessels are never compatible with E15 (15% ethanol). It is not permitted by federal law to use E15 fuel in boats (as well as motorcycles, off-road vehicles and power equipment), voids the engine warranty, and it has been proven to cause damage to marine engines. It also causes engines to run hotter and contains less energy than E10. Recreational vessel engines may only use gasoline containing no more than 10% ethanol (E10).

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Originally posted by markemark:

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Vehicles with electronic timing will always perform better on Premium fuel, given several tank fulls to set adjustments to the timing and fuel maps.

I agree with that statement. The proof is when I started towing over the Appalachians. With the recommended 89 octane it’ll drop 3 gears to maintain 60 mph upgrade. With 93/92 octane it’ll only drop 2 gears for the same mph towing the same load using cruise control and Not using Tow-Haul.
I only use 93 octane continuously for the 8 months I tow.