I have used a pressure washer to get algae off of a pool.
The
water slows the jet down so much that you have to be very, very close for it to
work, so you would be
cleaning a very small section, and since your holding it so close, it’s likely to damage your
paint.
Then there is the issue of holding a reaction jet in Your hand, so staying next to the Boat is going to be tough.
So easy to just wipe the boat down once a month so no scraping is required, if your scraping regularly, likely you need a new bottom.