Magnesium is used to protect aluminum or aluminum/zinc alloys (die cast, white metal). Magnesium anodes could be used in fresh water but cost more and disolve faster than zinc for about the same protection for metals found on most trawlers. Magnesium anodes disappear very fast in salt water. My zinc anodes last about 10 years in fresh water and short season on the Great Lakes. ________________________________________________________________ Sign Up for Juno Platinum Internet Access Today Only $9.95 per month! Visit www.juno.com