If the 15 degree tip doesn't cut it like you want try stepping up to a turbo tip, hold the tip back about 12" from the boat and then move in closer until you get the desired amount of cleaning action.
I power wash my boat all the time and I cant see it herting the paint or finish but the one thing you need to stay away from is stickers and pinstripe.
For a glass boat, I'd recommend going to Lowe's and getting some TSP (TriSodiumPhosphate) and following the directions. It does a great job of cleaning the grunge off boats with a scrub brush. After that I'd follow up with some Simple Green and then a final wipedown with Acetone. Any stains left after that will require more serious deep cleaning.
