We have a black boat and keep it in a slip all summer long. I know, itís really bad for the gel coat, but we have no other option over here.
I am cleaning the boat in the water each week to ensure all the scum that builds up around the water line is removed. Itís allot easier to do it once a week than wait for a month or so and then try to get all the dirt off.
The biggest concern from my side is the chalk stains that appear on the black hull. I have been told that wiping down the gel coat with a 1 part vinegar 3 part water solution helps remove these stains.