using ethanol even e-10 attracts moisture. I avoid it at all costs. If you have to use it i would suggest an additive to help with that. Boats run in wet environments and we don't need more moisture attracting substances. Is it safe to use? yes, but again i have heard from man mechanics that e-10 is good for about 30 days. Most of the time boats don't get used like cars where you are running thru the system on a daily basis.

And i would never store it with ethanol gas over the winter. I think the stuff is crap and always use 91 NON eth gas from my weed wacker all the way up to my boats and toys.