I've used a lot of Varathane varnish (both oil and water-based) in my house and had very good luck with it. The floors, baseboards and trim (all oak) have the water-based stuff and it has done very well, including the floor I build sails on which gets pretty hard use. So, a couple of years ago I bought a can of what they call their "water-based spar urethane" to try on a boat and some snowshoes. In a damp environment a lot of it eventually peeled. I kind of get the feeling that if it's applied on a surface that is waterproof and very stable (like epoxy) it works reasonably well, but on a more natural surface that may experience more expansion and contraction with temperature and humidity/dampness changes it may not work as well. If moisture can get under it, it tends to turn whitish and peel in situations where previous oil-based stuff survived. For lack of a more scientific term, the water-based varnish just doesn't seem as "sticky" or as well adhered to the surface. Maybe somebody else has had better results with it, but for serious boat stuff, I'm sticking with Captain's Varnish which has always worked well for me.