I don't know much about these things, but I would think varnish for marine yachts will not let off anything as long as its well soaked after coating and drying to remove any loose outer coat bits. I mean, environmental agencies wouldn't allow it to release junk into the water would they? And it has to be tough to put up with the limpet things that attach to the outside.
I'm just guessing really, but it's a reasomably educated guess.