Cleaning with Oxalic Acid: The $1 "The Works" Works
A lot would depend on what type of stains and deterioration you've got. Read Maine Sail's "Tips for a great buff wax" which is posted always on top of the "Ask All Sailors" postings as a sticky. That's sure to get you a good result for the topsides (hull).
Some have mentioned oxalic acid based cleaners. Oxalic acid works very well to remove rust stains, tannin stains and mineral deposits. More than one application is usually necessary. And don't let it remain on painted or metal surfaces. It won't cause immediate reaction with these finishes, but over just a few minutes or more it can dull the surface sheen.
About six months ago, I had great results removing the light brown tannin stains from near the water line on my hull with an oxalic acid based tub and shower cleaner product. See the attached picture of my test section before I proceded with the whole hull. I also noticed that it restored a bit of shine to the gelcoat. It occured to me that over the years, perhaps my whole hull (topsides) might have developed hard mineral deposits. So I applied the product all over with just staturated paper towels. Without any other work, the topsides looked cleaner and whiter than prior efforts with even wet/dry sandpaper and polishing compound. I did a bit of the newly cleaned hull with polishing compound and wax. Then I did a bit with wax only. The wax only section wasn't much different than the polishing compound section, so I just finished the whole thing with wax.
Best yet, the product I used is available at the DollarTree store for yes, $1.00. Primary active ingredient is oxalic acid. One bottle was enough for my hull. But buy two. You can afford it! Here's a link to the product.
http://www.dollartree.com/cleaning-...Tub-Shower-Cleaner/212c256c256p6065/index.pro
This product works great removing rust and tannin stains from sails as well. Just dab some on the rust stain with a small paint brush. After a few minutes you should notice the rust looking lighter. Repeat until gone. Then rinse off with fresh water. Best to apply on a cool day so the product stays wet longer. My sails are Dacron synthetic. Where I did apply the product, I haven't observed any damage or accelerated deterioration. But get a second opinion.
