In my freshwater experience with VC 17m, I have always wiped a few
spots with Interlux 216 Thinner and went ahead with the painting. It's
worked great for me since 2000. This year I will only need to touch up
a few areas. I haven't had to paint the whole bottom in three years
and have always prepped the bottom the same way. A little 216 wiped
over a couple of spots that the pressure washer didn't get too clean is
all that I've ever needed to do. Good luck.

Keith