Per, Good to hear from you again! It's been a while.
I just finished putting a couple coats of Epifanes on my caprail last weekend. If the underlying varnish is in good shape and you just need to rough it up for the next coat to adhere, try a green Scotchbrite pad. I give mine a hand scrub to knock down the gloss, then wipe clean of any dust. The best part of this is the minimal dust that results and the ease of scuffing the varnish.
This time I tried a new product from Epifanes called Wood Finish Gloss. It doesn't need sanding between coats which really cuts down the application and drying time needed. The instructions say to wait 24 hrs between coats, but I read elsewhere that, without sanding, it can accept a 2nd coat under ideal conditions after 8-12 hrs. I tried it after 10 hrs and it seemed to work well. It can be thinned with mineral spirits or topped with the Clear Gloss Varnish. Since I was after protection, not perfection, I did neither. We'll see how it holds up after a summer on the water. If I like it, I might use it on my doors and window trim this fall.