service life of mooring topchain

[Megunticook]

Installed a new 1/2" American-made (Acco) hot-dip galvanized topchain on a mooring in Penobscot Bay, Maine back in 2014. From October to May it sits in the mud at the bottom of the harbor. It's showing surprisingly little rust. About how many years do you suppose I might get from this chain before it needs to be replaced? From what I was reading online, I expected maybe 3-5 years, but now I'm thinking it might be well over 5. What have others experienced?

Interestingly, the only real corrosion I'm seeing in any of the mooring tackle is in the shackle holding the mooring buoy to the swivel (diameter of the shackle hasn't changed but the galvanized coating is completely gone, the U part of the shackle is completely rusted and showing some pitting--thickness still good but I'm sure that will start to dwindle. Is that because it's closest to the surface (light and oxygen?).

The swivel and other shackles still look good--a little bit of suface rust here and there but no pitting yet.

Haven't looked at the bottom chain and mushroom anchor yet but am planning to have someone inspect those soon.

[Carl Thunberg]

I'm not that far from you, and I get roughly 7 years out of 5/8 chain. 1/2 inch chain would be somewhat less. I have my own SCUBA gear, so I inspect my chain annually. Dropping the chain to the bottom during winter extends the life of the chain considerably. Swapping the chain end for end after about 3 years also helps, but it is a lot of work. Just one person's experience. Your mileage may vary.

[Joe Myerson]

Bourne, Mass., where I have my mooring, requires a biennial inspection of the mooring. I think much of this is part of the "employ locals act," as the inspection must be performed by a licensed mooring contractor. That said, I think my chain is replaced about every three inspections, or six years. So seven years sounds about right.

--Joe