Plain Water and...
... a pressure washer. Several years ago we bought a Karcher 1200 psi pressure washer that was at Costco and it has really worked out well. In the Pacific Northwest one of main problems is mold and mildew - birds that sit on the top of the mast, dust that settles out of the air, and a humid (wet?) atmosphere all conspire to turn the topsides green then black. Every nitche collects the stuff. Along comes the pressure washer and it can all be blasted away with just plain water. No soap, detergents, chemicals, or anything. One of the best parts (don't tell anybody) is my wife really likes to run it!See if you can find someone in your marina that has one and talk to them about it. Maybe they can give a demo?From an environmentally holistic perspective, the idea that one can use just plain water sounds really good; however, somewhere there is an electric power plant generating the electricity that runs on hydro, nuclear, oil, gas, or the like so the pollution source is in effect transferred to there.