I use shell gas in my car and sometimes my boat. Shell regular 87 is 10% ethanol, 89 is 5% and 91 is 0%. The 89 is 5% because it is a 50/50 mix of regular and premium.
I run the regular gas in my boat without issue. If your motor only requires 87 then there is no reason to run anything with a higher octane rating. The ethanol gas is fine as long as you run your boat on a regular basis.