You can wash and wax your boat all you want but it seems those pesky little water spots are inevitable. While regular washing, drying with a soft towel, and waxing are great ways to help prevent spots, there are measures you can take to remove them when they do appear. Before use of any of the below products, methods, or water spot removers make sure to read the directions and first test the cleaner on a small area of the hull. It is usually recommended that products be applied in a shady or cool area, as opposed to being in the sun. Some methods also work for calcium build-up on an outboard engine and lower units that are exposed to heat exhaust. Avoid cleaning your boat in the water to reduce the risk of toxic materials spilling into the water.
Try the Following Water Spot Removal Methods:
1) BABE’S Spot Solver
BABE’S Spot Solver is specifically developed to remove hard water spots caused from mineral build-up. BABE’S Spot Solver is a non-abrasive solution designed for all gel-coat, glass and chrome surfaces.
2) Vinegar and Water (homemade)
Mix one gallon of water with one cup of vinegar. Rub spots with a soft cloth. A few applications may be required before spots are removed. Note that after this use your wax will most likely be gone. Don’t forget to re-wax. An actual product on the market called Cleaning Vinegar works really well.
3) Lime Away / CLR
Though they are fairly aggressive products, CLR and Lime Away will also work, and many swear by them. Use these for the more severe cases of neglect.
To make your own, mix one part Lime Away and 10 parts demineralized water. It works best while boat is still wet after use. Spray it on and wipe with a soft towel. Don’t let it sit for a prolonged time. Rinse away immediately. Follow with a hull cleaner and wax.
4) Isso Fiberglass Reconditioner
Restores color to faded fiberglass. Removes oxidation and chalking, water-line, water spots, tars and oils.
5) Other Household Cleaning Products
Some use shower cleaning products such as Shower Clean and Lysol. Like most other methods, these products work best when the hull is still wet.
6) Extra Tidbit
For a yellow stained hull, lubricate it with WD-40 spray.
The article above was compiled from the link: http://waterski.about.com/od/boatmaintenancetips/a/boat_spotremova.htm