Whew! That was close!

[Sailmonkey]

Originally Posted by toddster8

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.

This!

I’ve seen it to a lesser degree in parts of Texas and Louisiana mud bottoms.

[Sailor647]

We were at anchor for 16 days straight - from the evening of December 31 through the morning of January 16.

The anchor chain was last thoroughly inspected in La Paz before we crossed the sea, on December 23. New tags every 25 feet. We anchored for two nights in Isla Isabel. I reviewed video I took of dolfins on the bow from Isal Isabel to La Cruz, and the chain looks fine - as far as I can tell from the video. (The dolfins are a little distracting.)

It wouldn't do any good to get rid of the swivel, as the anchor is stainless also.

There is another boat that lost their anchor yesterday in the same area. I don't know how they lost it...if they physically dropped it from the boat without a chain, or if it became disengaged from the chain like ours almost did while their boat was anchored. I'll try to find out.

We were anchored near the yellow buoy that marks the old ship wreck at the entrance to Marina La Cruz. How could an old shipwreck cause stray current?

Long shot, but would plugging our Honda 2000 generator into our shore power outlet (on board) produce enough stray current to cause this? We ran it for a total of 6 - 8 hours during the 16 days at anchor while we ran the watermaker. The boat would have been 150 feet away from the anchor (how much chain we had out).

Thanks again for all the help.

[Sailor647]

Originally Posted by zeehag

i figger someone dumped old batteries down on the bottom.

The lead in the batteries is too valuable in Mexico. They wouldn't be dumping them in the bay if there are pesos to be earned.

[a64pilot]

If it were stray current with the current coming from the Boat, then surely the wasting would be worse at the top of the chain closest to the boat? Surely a chain wouldn’t be a good conduction with all those loose links?

[model 10]

Belive it or not, there is no way to re-cycle batteries in much of MX and central America.
I'm going to guess that the generator was grounded to the boat. The stemhead fitting made contact with the chain. The stainless steel at the end was enough resistance to cause the chain to burn through with the poor contacts at the end of the chain.

[Cheechako]

Are you sure you just didnt notice it before? That would be highly unusual. Do you have a generator by chance? If so you may have stray current issues for sure. On aluminum boats we were unable to wire generators per ABYC due to concerns like that happening.

[Diesel Bill]

Originally Posted by Ecos

Belive it or not, there is no way to re-cycle batteries in much of MX and central America.
I'm going to guess that the generator was grounded to the boat. The stemhead fitting made contact with the chain. The stainless steel at the end was enough resistance to cause the chain to burn through with the poor contacts at the end of the chain.

I replaced 2 - 6 volt golf cart batteries in La Paz in 2016. We humped them from the boat up to the dumpster and put them on the ground where the trash scavengers could get them. I was throwing trash when the guy who goes through and recycles every day came by on his daily rounds. When I told him the batteries were there for him to take He said that He didn't want them. If I was in the states I would have taken them in for recycling or saved for cores.

[boatpoker]

Originally Posted by toddster8

Your chain might be just what it takes for current to flow. And lots of microbes love to munch on iron.

I don't see any iron involved.

[boatpoker]

Originally Posted by a64pilot

If it were stray current with the current coming from the Boat, then surely the wasting would be worse at the top of the chain closest to the boat? Surely a chain wouldn’t be a good conduction with all those loose links?

Any waste would manifest under water at the junction of two different metals (ss and galvanized steel).

Correct, chain would not be a good conductor with all those loose links which is why I qualified my supposition as "intermittent". i.e. when the chain was pulled snug due to wind or current. A constant stray current would have eaten through that chain in a couple of days or less.

[Paul L]

Is there any new corrosion visible on the anchor, assuming it is also galvanized?
Possibilities:
Current running through windlass from bad ground or worse wiring.
You dropped in a toxic waste dump that had some nasty chemical sludge on the bottom.

[JPA Cate]

Yeah, I immediately thought of acidic runoff, too, but it is only those few links where the galvo joins the swivel, and normally, at anchor, one has 20 or 30 ft. on the bottom, the rest being in the catenary heading up to the roller. Since it is only a few links, that points away from an acid anchorage.

Ann

[Paul L]

Originally Posted by JPA Cate

Yeah, I immediately thought of acidic runoff, too, but it is only those few links where the galvo joins the swivel, and normally, at anchor, one has 20 or 30 ft. on the bottom, the rest being in the catenary heading up to the roller. Since it is only a few links, that points away from an acid anchorage.

Ann

The links close to the anchor could have gone deep enough to sit in a chemical soup that the links on the surface didn't. Who knows what might have been dumped out in that anchorage in front of a dredged marina.
Just a possibility.

[danielamartindm]

I think that in general, we accept rusted anchor chain well beyond the time that we should. The reason is that it's expensive to replace; but to what single piece of gear do we entrust our innocent, oblivious, sleeping lives more?

[Paul L]

Originally Posted by danielamartindm

I think that in general, we accept rusted anchor chain well beyond the time that we should. The reason is that it's expensive to replace; but to what single piece of gear do we entrust our innocent, oblivious, sleeping lives more?

While this chain was old, 1988, it was regalvanized 3 years ago. The galvanization should still be good at that point, especially if the chain was end for ended. Not sure what these links looked like when the anchor was set.

[a64pilot]

Steel is essentially Iron is it not?
I have no idea myself, but would sure keep an eye on it.
If it’s stray current, it will repeat when your anchored elsewhere, but if it was somehow something to do with that particular anchorage, then there won’t be a repeat?
My guess is that is the only way you will find out, but until I was sure, I’d pull anchor every day, and maybe have a second anchor out on rope rode just in case?