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Old 18-01-2018, 10:47   #1
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Whew! That was close!

After being anchored for two weeks continuously in the anchorage at La Cruz (by Puerto Vallarta, Mexico), we pulled the anchor to move and canít believe how lucky we were.

The links next to the anchor swivel were nearly rusted through. Picture attached. We can just imagine being set adrift in the middle of the night in a crowded anchorage or ending up on the beach while we slept soundly away.

We have the 46# Ultra Anchor and love it. Holds like a champ. Always. Weíve been cruising Mexico and the Sea of Cortez since 2015 and havenít had a single anchoring issue. Until now.

We know dissimilar metals (stainless steel and galvanized steel chain) will react when in salt water, but we were startled at the pace it degraded the chain. And why all of a sudden?

We've heard of other "lost anchors" in this anchorage, but don't know the exact particulars.

The chain is 1988 vintage Acco G4 and was re-galvanized in 2014. The company did a superb job, as there is still no rust on it Ė except the 5 links at the anchor.

The Maxwell 1500 windlass was new in 2014 also, and properly installed and grounded. The boat has a complete bonding system in place, and (after inspection) all the green wire and terminals that attach to all the through hulls, engine, tanks, etc, are in good, non-corroded condition.

Can you share any wisdom as to what would cause the chain to rust through THAT FAST?

Thanks for the help! We appreciate it!
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Old 18-01-2018, 10:57   #2
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Re: Whew! That was close!

I'm curious as to why you have a swivel? And a thank you for giving up a spot in la Cruz, I'm planning on being there in March. ;^)
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Old 18-01-2018, 10:59   #3
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Re: Whew! That was close!

It came with the anchor. Works great. Doesn't bind. Helps the anchor to sit in the bow roller when being retrieved.
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Old 18-01-2018, 11:03   #4
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Re: Whew! That was close!

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Originally Posted by goat View Post
I'm curious as to why you have a swivel?
I use one as it makes it supremely easier for the anchor to orient itself properly when loading onto the bow roller. It also reduces twist in the all chain rode.
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Old 18-01-2018, 11:21   #5
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Re: Whew! That was close!

Quote:
Originally Posted by Sailor647 View Post
After being anchored for two weeks continuously in the anchorage at La Cruz (by Puerto Vallarta, Mexico), we pulled the anchor to move and canít believe how lucky we were.

The links next to the anchor swivel were nearly rusted through. Picture attached. We can just imagine being set adrift in the middle of the night in a crowded anchorage or ending up on the beach while we slept soundly away.

We have the 46# Ultra Anchor and love it. Holds like a champ. Always. Weíve been cruising Mexico and the Sea of Cortez since 2015 and havenít had a single anchoring issue. Until now.

We know dissimilar metals (stainless steel and galvanized steel chain) will react when in salt water, but we were startled at the pace it degraded the chain. And why all of a sudden?

We've heard of other "lost anchors" in this anchorage, but don't know the exact particulars.

The chain is 1988 vintage Acco G4 and was re-galvanized in 2014. The company did a superb job, as there is still no rust on it Ė except the 5 links at the anchor.

The Maxwell 1500 windlass was new in 2014 also, and properly installed and grounded. The boat has a complete bonding system in place, and (after inspection) all the green wire and terminals that attach to all the through hulls, engine, tanks, etc, are in good, non-corroded condition.

Can you share any wisdom as to what would cause the chain to rust through THAT FAST?

Thanks for the help! We appreciate it!
The metal wasting (thinning) on that link certainly looks like galvanic corrosion to me, as does the fact that only the first 5 links or so are rusting. So that strongly suggests a battery-type reaction btwn the SS swivel & the re-galvanized chain. How long had your anchor been deployed before you pulled it up?

Maybe Boatpoker will respond. He's a certified marine surveyor in this area and recently commented in a related thread.
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Old 18-01-2018, 11:24   #6
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Re: Whew! That was close!

Perhaps those links were being scrubbed by the sandy bottom, wearing off the galvanizing? Although I would expect that in normal conditions more chain that that would be dragging across the bottom.
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Old 18-01-2018, 11:36   #7
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Re: Whew! That was close!

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Originally Posted by Sailor647 View Post
After being anchored for two weeks continuously in the anchorage at La Cruz
Time is a critical element here. Galvanic corrosion with these metals would be a very slow process, from many months to years. Stray current corrosion can be very quick, from days to weeks.

If this truly occurred in only two weeks, it is inconceivable to me that you are dealing with galvanic corrosion.

Your bonding system does not protect you from stray current.

WAG .... I suspect an intermittent stray current, possibly due to the variable contact (continuity) through the links of chain as it moves. If I am correct, this would be difficult to prove as your volt meter would only show voltage when all links are in firm contact
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Old 18-01-2018, 11:43   #8
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Re: Whew! That was close!

i noticed my chain after raising anchor in la crus an dbeing anchored for a few weeks, chain lost galvo. the chain itself is still good and has survived many months of anchoring in barra before residing semi permanently on my foredeck or dock until my repairs are complete.
none of the material of the chain has been lost.
i figger someone dumped old batteries down on the bottom.
i know where the 3 ft depth rock is located also, not far out the entrance to marina la cruz. excellent anchorage i didnot like. loved la cruz town, and bucerias, but the anchorage sucks. it is not protected from open ocean , and is the depository for dredging spoils from original dredging of marina.
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Old 18-01-2018, 11:51   #9
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Re: Whew! That was close!

Quote:
Originally Posted by boatpoker View Post
Time is a critical element here. Galvanic corrosion with these metals would be a very slow process, from many months to years. Stray current corrosion can be very quick, from days to weeks.

If this truly occurred in only two weeks, it is inconceivable to me that you are dealing with galvanic corrosion.

Your bonding system does not protect you from stray current.

WAG .... I suspect an intermittent stray current, possibly due to the variable contact (continuity) through the links of chain as it moves. If I am correct, this would be difficult to prove as your volt meter would only show voltage when all links are in firm contact
Boy did I ever miss the boat on this one, pardon the pun. And to think I had just read your well-written memo! Thanks for responding, and correcting me re: galvanic vs. stray current corrosion. Hey, at least I didn't use the term electrolysis.
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Old 18-01-2018, 11:57   #10
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Re: Whew! That was close!

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Originally Posted by zeehag View Post
i noticed my chain after raising anchor in la crus an dbeing anchored for a few weeks, chain lost galvo. the chain itself is still good and has survived many months of anchoring in barra before residing semi permanently on my foredeck or dock until my repairs are complete.
none of the material of the chain has been lost.
i figger someone dumped old batteries down on the bottom.
i know where the 3 ft depth rock is located also, not far out the entrance to marina la cruz. excellent anchorage i didnot like. loved la cruz town, and bucerias, but the anchorage sucks. it is not protected from open ocean , and is the depository for dredging spoils from original dredging of marina.
Chain lying on old batteries seems a little far fetched but I've seen stranger stuff.
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Old 18-01-2018, 12:33   #11
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Re: Whew! That was close!

Poor negative cable connection to your anchor windlass circuit ???
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Old 18-01-2018, 13:41   #12
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Re: Whew! That was close!

Bizarre.

When was the last time you inspected those links, just so we have a baseline of how long it could have taken. Did they look fine at the start of those two weeks or did you not take a close look?

I assume when the anchor is weighed those links are above deck and not even yet at the windlass. Seems highly improbably that it would happen on the boat.

Some of it looks possibly like wear, given the scalloping, but would seem impossible for it to happen that quickly much less over months. One support of it being wear is that it's on the link that is right up against the one on the swivel, which cannot articulate. Just a theory.

On last point. If you insist on using a swivel, I would pitch that one and buy a new one.
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Old 18-01-2018, 13:56   #13
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Re: Whew! That was close!

That kind of corrosion in two weeks seems astounding! But I'd offer another theory - bacterial metabolism in anoxic sediment. The theory is a bit much to go into in a quick post, but essentially, given the right kind of muck layer, the microbes make the sediment/water interface into a big battery. Your chain might be just what it takes for current to flow. And lots of microbes love to munch on iron.

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Old 18-01-2018, 14:11   #14
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Re: Whew! That was close!

If your picture doesn’t deceive me then it looks like the most worn part of the second link has no rust on it, which might suggest mechanical abrasion. Against what? I don’t know. If it were against the edge of the swivel then it ought to have some wear too. But it is the first link that can move freely and if you were on a short scope it might have moved back and forth (or up and down) with your boat. Even so it’s hard to imagine that much wear in only two weeks.
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Old 18-01-2018, 14:25   #15
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Re: Whew! That was close!

Quote:
Originally Posted by toddster8 View Post
That kind of corrosion in two weeks seems astounding! But I'd offer another theory - bacterial metabolism in anoxic sediment. The theory is a bit much to go into in a quick post, but essentially, given the right kind of muck layer, the microbes make the sediment/water interface into a big battery. Your chain might be just what it takes for current to flow. And lots of microbes love to munch on iron.

See this in a lot of anchorages in the Pnw. Anchor tips and chain come up black often wondered what would happen if you moored in one for a decent stretch.
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