Yep, I'm a boat owner and all of that is in every manual.
Ethanol and alcohol is not good for those motors.
For one thing, they'll eat through your gas hoses that supply your motors.
They also are the cause of rattling valves.
In other words, it sucks.
It will void the warranty of your boat motor as well.
I know this because I am a big believer in reading my manuals.

That's why I only buy our gas from reputable stations.
It's serious business.
If you don't and you buy the cheap gas, you could be out on the lake and your boat could catch fire and/or blow up.
It's no laughing matter at all.
Even if your boat starts fire and you get off your boat, if the water is cold, you have to hope you can make it to shore before you get too cold or drown.
This is where gov't should stay the hell out when it doesn't know the problems it is mandating.
Randy