I really question your boat mechanic Jeff or how he came to this conclusion since all marine gas sold at marinas on the water are ethanol free reason being that ethanol draws moisture . It would be nice to get 87 ethanol free but it's a hard find and 91 ethanol free is better than 87 with ethanol . I run ethanol free 91 in all my small engines and Yamaha is where it's at for ATV's . Mines carbed and even at 40 below she fires right away . Everything gets seafoam , even the truck when I'm feeling nice . The only real advantage to EFI to carb is when running in mountains and such because a carbed machine needs rejetting .
TD