When I was having my upholstery redone, I used a pressure washer on my glued down carpet and followed up with a carpet cleaner. Made a big difference. Just be careful where you aim the pressure washer.
I use a pressure washer as well. Also want to use a wet dry vac afterwards to get the water out. Keep away from amps etc. Just be very careful and do not rush. I do not suggest this if you have a wood floor though in your boat
Call a carpet cleaning company. Tell them you want your boat's carpet steam cleaned. They'll probably do the whole thing for around $100 and it'll look great.