I dont like the idea of using the pressure washer personally. I have an older boat, and the carpet was horible whe nI got it, now its much better, but by no means pristine.
When I was the boat, I use a scrub brush on a pole. I wash the carpet with the soapy water and that brush as well. The reason is I can work the soap into the carpet using the prush to loosen up the dirt. I then take a shop vac and vacume out as much as I can. Then, I co back with a hand held carpet cleaner (Bissel Little Green Cleaner) and go over everything with it.
Its amazing how much dirt comes up with the carpet cleaner, even after the shop vac.
For the summer quick cleans or spot cleans, I just use the carpet cleaner.