I have been using FSR or Fiberglass Stain Remover for years, (and just today as I hauled out) Put some in a spray bottle cut heavily with water. Shake to break it up (it is a gel) so the pick up doesn't clog so easily. Spray on. Five minutes hose off. I keep a spray bottle on the boat all season long. It will take off your polymer, ceramic or wax coating... Also good idea to hose off trailer too.
http://www.striped-bass.com/Stripert...+stain+remover