I need a paint or a plywood dinghy that will stick to epoxy and varnish. Must stick even when in water for longer periods of time.
Rustoleum does not seem to do it, although it might be a previous layer of paint that is causing the bubbling and flaking.
Most paints are not really formulated to work when submersed. Why not use Interprotect 2000E as a "paint". If nothing else, it would make an excellent primer coat for another paint to tie to.
In my experience, 1 part polyurethane paints like interlux Brightsides or Toplac tend to have a short life when exposed to water.
If you are painting a dingy (which is going to sit in water) I recommend you either do as Dan suggested, or paint the bootstripe down with bottom paint and then use the poly above the waterline. Keep in mind the inside of the dink will likely have water sitting in it much of the time too. Bilgekote might work out for the inside.
I have also heard (but have no positive experience with) deck paints (as in home deck). They are 1 part poly or Alkaloid (sp) paints formulated to be used where they will get wet.
2 coats of rustoleum on the bottom over2 coats of epoxy lasted 2000 miles for us over the last 6 months. The vast majority of that was being towed behind the boat, occasionally hauled up on deck for a scrub, or when going offshore. I can post before/during/after pics if you're interested. This summer we're builing a sailing version of the dinghy, so I'm also interested in what input others have.