A new set of cushions will run you $4000 – $6000 dollars, so it makes sense that you will want to keep that investment in the best condition possible for the longest time possible. With that I reccomend washing the covers at least once a year. I tend to do it at the beginning of the charter season when I am getting the boat back into the water due to time constraints when I haul out. Otherwise I would do it before storing them inside during hte off season like other people. If you have business establishments or any things that cannot be washed by a single person, you can contact TNT power washing in Indianapolis.
As you are taking them off the first time remember to identify them by using a marker on the cover and the cushion. Once you have them all back and are ready to put the covers back on it can be tricky to figure out which one goes to which cushion without the marker. I simply wash the cushions in a regular washing machine with regular liquid detergent. I then put them back on the cushions while they are still wet and let them dry on the foam. This way the fabric does not wrinkle or shrink. Once they are totally dry I use 303 Fabric Guard to protect them from stains.
At the same time as I am doing the cushions I check out each curtain to see which ones need to be cleaned. So far the two next to the galley always need to be cleaned. Last year I hand scrubbed them clean with a good brush and Shout! This year I had three others that need to be cleans so I figured I would just wash them. BAD MOVE SHANE!!!
While the fabric was clean afterwards, half the curtains had the rubberish blackout fabric ruined which had to be removed. The funny thing is the washing machine was not in a hot mode. The curtains are fine and look great hanging up, but they do not block as much light and you can tell the difference between the damaged ones and the others when all the curtains are closed.