Some varnishes a perfect right out of the can. You now know that it has to be thin enough to lay flat before it stats to set up. This can very according to the temperature of the day etc. If the boat is hot from being in the sun it can set up the varnish before it lays flat. I varnish in the morning on a cool boat (no pun) in a garage.

I'm no expert. I now use an imitation bagger brush $6 with good results. I find the foam leaves me with dry spots on occassion. The whole viscosity issue comes with experience. There's nothing more frustrating than to have it set up with streaks before it gets a chance to lay flat. I feel better too thin than too thick.