I have used a Karcher electric pressure washer that came with 2 different wands for the last couple of years to clean my topsides and canvas and it works quite well. I first got it when, as I was scraping bird dung off my canvas with my fingernail, I saw a guy in a neighboring slip easily doing the same task with a pressure washer which he recommended highly.
I like to use it in conjunction with West Marine boat soap. In fact, I'm going to use it tomorrow to do a cleanup.
I recently bought a kit with another wand, angle connectors and nozzle for use around the house.
I have not had any problems with the washer damaging anything on my topsides or canvas. I don't know how it would work for a bottom job. Since most of the boatyards in my area don't allow DIY bottom jobs, I will probably never know.