Last season, I replaced the anchor chains on my floating dock. I chose Grade 30, 5/16″ galvanized chain at the recommendation of my local hardware store (¼” and 3/8″ are also common). They were well priced—about $3 per foot. I should have replaced my chains long ago, but it’s impossible to predict the longevity of galvanized steel in freshwater since the rate of corrosion depends on many factors—quality of the chain, water chemistry, friction, vegetation, and wave conditions all play a role. Even water hardness matters: Tom Langill, the technical director at the American Galvanizers Association, writes in an online article that galvanized steel lasts longer in hard water because carbonates deposit a protective film on the zinc surface, which slows corrosion.
Several years ago, Practical Sailor magazine tested seven 5/16″ chains, ranging from cheaply made links to pricey stainless steel. Though its tests were done in salt water (which is more punishing than freshwater), after just two and a half years, all the chains were too corroded to safely moor a boat. The cheapest chain fared the worst. The chain it recommended, the Acco Grade 30 chain, provided the best balance of corrosion resistance and price (though the Acco chain can cost 30 to 50 per cent more). Alarmingly, the stainless steel chain appeared to be in the best shape, but was the first one to fail the magazine’s break-strength test.
Anecdotal evidence suggests that galvanized chain lasts twice as long as the equivalent unplated or uncoated chain. Higher-quality chains with thicker galvanized coating (such as the Acco Grade 30) last even longer. Stainless steel is not worth the expense, since after long periods of submersion, its flawless appearance can hide underlying weakness.
Inspect chains yearly and replace them if links are thinning or corroded.