I originally bought MinWax Helmsman Urethane only to be told by the company not to use it on boats. Then I check out Z-spar's Captains's varnish which is liked and used by many on the board and it says not to be used under the waterline. Z-spar's Flagship doesn't say this. I read in the archives that Spidey used a $6/gallon WALMART closeout spar varnish with UV protectant. This is all confusing. Any thoughs why these companies have these cautions and does it make that much difference???

John