Wet carpet completely. Use a non bleach laundry detergent mixed well in a bucket of warm water. Pour some on the carpet and brush with a nylon brush. Cover the entire carpet. I start at the front and work my way back. Rinse completely. Parking the boat on a slope helps with this, just be sure and pull the drain plug. After all soap is out, shop vac the carpet. Before it dries, spray it with a 50/50 blend of Downey Fabric Softener and water. Rinse carpet again. This time when you shop vac the carpet use a clean nylon brush and brush against the grain on the carpet while you vacuum. I know this is a lot of work but trust me the carpet will look and feel like new. The fabric softener will cut down on future stains and it makes the next cleaning much easier.