I use NuFinish - a synthetic wax with a UV inhibitor. I still get the black streaks and they are difficult to remove. However, I wash the boat using a solution with a little soap and a little bleach - the black streaks come right off with the bleach. Twice a year I re-wax the boat. It was bought new in 2004, and although the trampoline remains tightly covered, the hulls get a good bit of sun exposure but still look new.