Purple power, works like a dream on everything I've used it on.
This pic, and the three after it show why I like purple power (cleanrite.com)
http://picasaweb.google.com/merc2dogs/Triton#5337315845697379442
I spent hours trying to clean a small section in the Triton and hardly made a dent in it with scrapers, scrub brushes and various other cleaners. the only cleaner the local store had was pp, brought it home mixed it 3:1 in a garden sprayer (water

p) soaked down the area under the cockpit, went above to get my deck brush, and when I came back down it was nearly spotless with all the crud in a puddle on the bottom of the sump.
I have never noticed any effects with bronze, but if you let it sit for a while on aluminum it blackens it, and will soften some paints. so I make sure to rinse it quickly.
quote from page:
Purple Power Industrial Strength Cleaner/Degreaser is Certified Biodegradable by the Scientific Certification Systems. It is biodegradable, phosphate-free and non-flammable. Purple Power has been rated as the #1 Selling Cleaner/Degreaser in the automotive retail market since 2003.
Yeah, I know I sound like a salesman, but I have no connection at all with them, and do recommend it.
Ken.