I've used Flecto's Waterborne varathane for below the waterline on a skin kayak , 5 coats on dacron fabric , no leaks.

: Hey Guys, Got another varnish thread to start. I'm down to the final
: finishing of my 16' Prospector and am ready to shoot a finish. I've used
: water-based laquers in the past on furniture I've built and loved the way
: it sprays and its quick drying attributes. For me, this is a real plus as
: I have to spray in a "knock-down" spray booth and have less
: problems with dust settling. I have recently seen a new exterior water
: based polyurethane finish from ZAR that seems to be a good product. Like
: all Poly's the label says above water-line use only, but the
: manufacturer's test seemed to perform well on wear, UV resistance and
: weathering. Anyone familiar with water-based exterior poly's. Thanks, Mike