As someone who owns a pressure washing company, the best advise I can give is to use common sense with a pressure washer. When used properly, there is nothing better for cleaning purposes. With the proper pressure washer and chemical application, it can be as easy as spraying a chemical on with a pressure washer and rinsing it off with a pressure washer. With that being said, a small tutorial for anyone that wants to purchase a pressure washer and use it for cleaning a boat.
Purchase:
There are two performance factors to look at, volume and psi. Manufacturers will push psi as the only thing to look at. The comparison that I use is an electric paint sprayer and a fire hose. The paint sprayer will put out 5000 psi but if you load it with water, not a whole lot of cleaning will be done. The fire hose will put out only 60psi, but the volume is what does the work. You will do a lot more cleaning with a fire hose than a paint sprayer. You need to find the right balance of pressure and volume. For boat cleaning, a pressure washer in the 1500psi range at 2-3 gallons per minute will do the trick. If the machine is rated for higher psi, that is fine as the pressure is adjustable simply by switching to a bigger nozzle (anyone with any questions on dialing in the pressure and volume, pm me and I will gladly help). Don't use the knob on the machine, as that lowers the volume coming out. You want to maintain the volume and lower the psi, not as difficult as it sounds.
With a boat, you will use chemicals to clean. Just using straight water out of the pressure washer is a terrible idea for cleaning purposes. Look at the chemical injector options on what you purchase. With the chemicals you use to clean a boat, I would definitely recommend what is referred to as a downstream injector. What this means is that the chemical is added to the water after the pump, and not before. The seals inside the pump are not very chemical resistant and improper use of chemicals in the pump will cause a pump failure, even as early as 10-15 minutes of use. The other option is a foam attachment at the end of the wand. This will inject the chemical and mix it with air right at the nozzle, resulting in a foam cannon to apply the chemical. The only problem I have run into with these attachments is wind and sun. The chemical dries quicker (never a good thing to let chemicals dry before rinsing) and it blows all over the place in a strong nough breeze.
The last thing is accessories. Make sure that the wand that you receive can accept different attachments. There are flexible nozzles, extension wands, adjustable stream nozzles, turbo nozzles (never use on a boat), and more accessories that I couldn't possibly list. This gives you the flexibility to clean any size and shape boat you can imagine.
So to recap, psi and volume, chemical application, and accessories.
The ideal pressure washer will probably run +-$300 for the best cleaning performance (either gas or electric, pluses and minuses to both). After you have dialed in the pressure washer, chemicals, accessories, and process you use to clean your boat, a boat that size I can do sides, canvas, and deck in about 35 minutes. My open bow sea ray I have down to a science and can knock that thing out on a trailer in under 15 minutes, inside and out.
I have several other tips and procedures on chemicals, processes, what to do and what not to do. If you are interested in anything or need brand recommendations, pm me and let me know.
