PS Advisor: 01/01/05
Zincs on Moorings?
I know that the chain on my mooring is galvanized, as are the swivel and shackles. The mushroom probably started out that way, too, but that was long ago. It would be a miracle if the mushroom, chain, and hardware were actually all the same grade metal, even when they first entered the sea. Why then, isn't it common practice to protect the rig with a large zinc or two?
Wouldn't you expect the addition of some zincs to extend the life of the mooring gear? This past season, I had a professional diver inspect my mooring and I was surprised to find that the first 20 feet of chain, the part that is attached to the mushroom and is always in the mud, was rusted and needed to be replaced. I asked him why a large zinc or two was not installed. He had no idea. He asked the guys who handle the mooring field for the local yacht club and they didn't really know either. I've taken a casual look at the literature, and there's never a mention of zincs. Why is this?
New York, NY
We put the question to Mike Muessel of Oldport Marine in Newport, R.I., who often answers diesel-oriented queries for us, but also has boundless experience in maintaining moorings. Here's his take:
"Having been in the mooring business for over 30 years and having seen my share of different problems, I've always taken the conservative route and generally followed traditional thinking in terms of what type of gear to use underwater.
"I always strive to keep the underwater equipment as simple and as straightforward as possible; that is, keep the number of underwater shackles to an absolute minimum, don't use swivels underwater unless absolutely necessary, and then use only top-quality swivels, and probably most importantly, don't mix metals, especially stainless steel with iron or steel. Galvanized steel is OK, even though the zinc on submerged chain and shackles only lasts a year or two, but I've never added a seperate zinc to a mooring system.
"One of the worst problems I've seen is the excessive use of stainless seizing wire on shackles. Just as rust never sleeps, neither does electrolysis on underwater gear. I suggest using only two wraps of thin seizing wire and I've considered using nylon wire ties as an alternative. We've used nylon ties above the water for years on the shackles that attach the chain to the mooring pendants with no detrimental results.
"Of course, now that I've gone to great lengths so say how I've never used zincs on my mooring gear, I have a confession to make. I noticed years ago the mushroom anchor on a Coast Guard lightship had a zinc on it..."