What caused this?

[FarCry]

The 10MM chain in the photo had been in the water for 2 years.

Here are all the details I can think of:
This is a moorage in a bay 50 yds from any other vessel.
There is no shore power within 300 yds.
There are no live aboard vessels in the bay.
The other end looks just as rusty, underwater.
The chain was purchased from a chandlery franchise that has a good reputation and they were perplexed with the cause as well. Especailly considering this happened in the middle of a length of chain.

What I did two years ago---
I set three sand screws, ran three galvanized 10MM chains to a galvanized swivel using galvanized shackles as needed, from the swivel going up to the mooring ball is where this disintegrating piece of galvanized 10MM chain was located. From the swivel there was 4' of chain, 3' of it looks fine and then it corrodes away like the other end that I have photographed. I was unable to get the shackle off the swivel to photograph it. The water depth is 12' with a sand bottom. I kept my 10K pound sailboat on it for the first year. There were no boats on it for a few months and then a J24 was on it for about 8 months. Fortunately there were no boats on it when my mooring ball broke free and floated to shore.

The "good" part of the chain is showing surface rust now that it has been exposed to air. It had no surface rust when I first pulled it out of the water.


What do you think caused this? How do I prevent it from happening again?

[tommays]

Being COMPLEATLY serious CHINESE CHAIN would be a good guess without having it tested







There are so many shady parts getting sliped onto the market

[Hartley18]

I'd have to agree with tommays. Can you get the chain tested?

Originally Posted by FarCry

...The water depth is 12' with a sand bottom. I kept my 10K pound sailboat on it for the first year.

Sounds like an ideal mooring to me! All we get around here is mud..

You didn't say how sheltered the anchorage was. Could it be possible to get significant layering in the water beneath you?

Only reason I ask: I've seen something similar happen where there was an steady outfall of warm brackish water from a nearby steel plant that caused mooring piles to fail at the salt/fresh interface - but that was rather unusual...

Cameron

[FarCry]

The chain is manufactured in Asia, shipped to Italy to be galvanized and then tested to meet European quality control standards. At least the previous statement is what I was told from the manager of the chandlery.

The mooring area is moderately sheltered, it would be very unlikely to get enough fresh water runoff to affect the salinity. I would not have assumed that fresh water could be worse than salt water on metal.

What would I have the chain tested for? The actual metalergy or the plating?

[Faster]

Was the worst damage in the vicinity of the shackles? Could you have localized galvanic corrosion due to the makeup of the shackles?

[FarCry]

Faster, I am not sure what you consider in the vicinity. The damaged piece of chain was 18' long from swivel to mooring ball. The area that failed was about 4' from the swivel and shackles. All of the chains that extend from the sand screws to the swivel are connected using the same (manufacturer) shackle. I dove the mooring Saturday and closely inspected every shackle, the swivel and every link of chain. Everything looked good, or at least as one would expect it to look after laying on the bottom of the sea for two years. There is no visible damage to any of the other existing components.

Before I forget, thanks everyone for your ideas.

[Maine Sail]

If this wear was located where the boat lifted the chain off the bottom from tides or wakes riding the boat up and down this is quite common. The intersection of the chain and the bottom of the ocean is where you will see the most wear and then the area right bellow the ball with be the second most wear as the links really grind on each other here more than anywhere else in the system.

That photo, from what I can see, shows link wear and it does not loo like corrosion. Look at the mid sections of those worn links and you'll see they are still almost full thickness but the wear areas are thin from grinding on each other. possibly under twist events The "hanging" or "suspended" links see much less wear than do intersection (with the bottom) or "twist" links (close to the ball). Sand bottom can also accelerate link wear, think sand paper..

Please don't ever size permanent mooring chain by the "working load". Mooring chain wears where the links mate 365 days per year and you want the thickest wire size your ball can float! You also want the heaviest chain you can afford to avoid shock-loading and have plenty of caternary..

Using 10mm chain, on a 10k boat, for a permanent mooring, is like anchoring with dog tag chain IMHO...

This is the chain I use for a 36 footer and contrary to what some will say it is NOT over sized!!

[poopdeckpappy]

If the galvanizing was poorly done to begin with, the galvanizing itself can actually accelerate the destuction of the metals

[FarCry]

HOLY CRAP Maine Sail!!!!!! I am man enough to admit that yours is way bigger than mine, chain that is. Either that or you have the worlds smallest hands.

Your theory was brought up by some other local folks that I quizzed before posting here. There are no real tides here (about 1' max) so when not in use the same links would be on the bottom of the sea. Others in my mooring field using very similiar installations have not suffered the same results. Some moorings are more than 10 years old with equally sized chain/boats and waves. When a boat is on my mooring the steady trade winds keep this piece of chain off the bottom much of the time but rarely is there enough pull to raise the weight of the swivel and the other chains. When no boats are on it, the mooring ball would be bouncing vertically 24/7 with the same links contacting the sandy bottom.

So your solution to prevent this in the future is to steal some anchor chain from the next cruise ship that comes into port?

What about a small submerged float to keep this vertical piece of chain from touching the bottom? Other ideas?

[artbyjody]

Originally Posted by FarCry

So your solution to prevent this in the future is to steal some anchor chain from the next cruise ship that comes into port?

Please, get video of that if that is indeed your next route!