Very often the word submersion means a boat that is moored all year. Since it's an exterior polyurethane, it's meant for the weather. But spar varnish and poly are actually designed for topsides that meet the weather and spray. Our usage of these products for canoes and kayaks is not in their technical vocabulary and therefore get an automatic "no" response. Helmsman holds up fine on canoes and kayaks. I've use it for years although I tried a can of Epifanes spar varnish and I'm impressed. It holds it's gloss longer than Helmsman in my opinion. Could be I did a better application job ??