If you have a white hull boat than carefully mist your hulls only with a bleach solution on a non wind day.Be very careful not to get bleach on anything else.If your boat is striped down to hulls only the cleaning will go smoother.The bleach will kill all the mold and loosen it up.Leave it on for a short time(two beers is about right) and do this a sunny day is best.Than wash and rinse it off.Buy some Barkeepers Friend and get some Chore Boy Golden Fleece scrubbing cloths(just like my mom used),put on some gloves and scrub off all that crap.Use a short bristle scrub brush to remove the dirt in between the checks on the non slip deck.Your boat will come back to life.Now wax and rewax and rig for the lake.
I like 3M marine ultra performance paste wax for that wet look.
Your boat will look great,Bill 404 21SE