The automotive combo products like TurtleWax or Meguilars', which a lot of small boaters use (but frequently!) just do not stand up to salt water. I have to admit I too am horrified at the thought of using a pressure washer on a boat; hard on the coatings and sealants. A regular adjustable hose nozzle set to a shower type spray will get the salt off just fine then wipe down with a chamois mop and/or microfiber cloth.
"There's the Right Way, the Wrong Way, and what some guy says he's gotten away with"