Has anyone ever broken their anchor chain at anchor?

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fuss

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I just wondered if anyone has actually experienced this. If you read up on wind strengths etc on anchor web sites, you see that there are conditions where the chain strength is exceeded. But its a web site and web sites are not always reality. I've anchored in a few storms and while the chain sometimes had alot of force on it, I never expected it to break. My boat is 20 tons and the chain 10mm but not high test.
 
Two years ago I was at an anchorage with another yacht whose chain broke but this was due to the quality of the chain and not the force of the wind. Chain was two weeks old, of European manufacturer and bought from a reputable chandler. Wind was no more than force 5. I had been considering whether my 12 year-old chain should be replaced but this experience led me to stick with what I had.
 
I've never heard of chain parting under the loads imposed by wind and waves but I know of a couple of cases where a shackle has given way (bad quality) or a rope to chain splice has parted (chafe).
10mm chain has a breaking load of around 5000kg; this is hugely more than the load imposed on a boat, even in extreme conditions. To break the chain the anchor would have to be jammed, because the pull out load on a normally set anchor doesn't approach the breaking strain of the chain.
What usually gives way is the anchor's hold on the seabed or a weak link in the system - shackle, swivel, joints of any kind.
 
My connector broke in about a force 3, which was the trigger that started my destuctive testing articles in YM. Manufacture of the connector was the culprit: the fracture was brittle, probably due to chloride stress-corrosion. This occurs when the hardness is excessively high, which in a 300 series component is almost certainly due to cold work in the extrusion process.
Fractureface.jpg


I have read of chain fractures but there was always another factor than load, e.g. corrosion, poor manufacture, etc.
 
I've only seen one example of (stainless) chain breaking and two boats on the shore after their shackles broke (the wind did a 180 and picked up at night). We want to sleep at night and use test chain with no swivel.
 
Tech question.

If the breaking strain of a chain is x kg, is there a difference in a snatch load (e.g. a boat suddenly snubbing up against a jammed anchor), and a steady pull (e.g. a boat at anchor and subject to a steady high wind. Ignore the sea state for the purposes of this enquiry pls)

I know there is elastic and plastic deformation, but it seems from observation on the farm that a sudden pull breaks chains more easily than a steadily increasing one.


Just curious :)
 
sarabande said:
Tech question.

If the breaking strain of a chain is x kg, is there a difference in a snatch load (e.g. a boat suddenly snubbing up against a jammed anchor), and a steady pull (e.g. a boat at anchor and subject to a steady high wind. Ignore the sea state for the purposes of this enquiry pls)

I know there is elastic and plastic deformation, but it seems from observation on the farm that a sudden pull breaks chains more easily than a steadily increasing one.


Just curious :)
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Yes. Impact loads are reckoned to deliver up to 10 times the steady load. The trick comes in estimating just what an anchor rode could be delivering. My guess is a lot less than x10 as there is considerable damping. Assuming the rode loses all its catenary at around wind force 6-7, wave action can then act directly on the straight chain between hull and anchor. However, the hull is not fixed and can move forwards to accommodate the force, assuming the anchor can hold it. So my guess is a factor of 2-4.

Message is - use a snubber:)
 
Acceleration Is The Factor In Snatch Loads

sarabande said:
.....If the breaking strain of a chain is x kg, is there a difference in a snatch load (e.g. a boat suddenly snubbing up against a jammed anchor), and a steady pull....../QUOTE]

A snatch load is a force caused by acceleration where Force = mass x acceleration. A rapid acceleration will produce a very high load compared to a slow acceleration of the mass.

A chain that is slack and is snatched tight is subject to a very large acceleration i.e. from 0 m/s to what ever the speed of the pulling device is in almost fractions of a second of time. Compare this to gently taking tension up and then increasing the pull slowly.

Do the arithmetic yourself.
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It's not the chain that I would worry about. Anchor loss is usually due to:

1 Swivel breaking

2 Shackle/swivel pin not being seized properly

3 Shackle/swivel pin thread corroded ..... I'm sure that is is due to poor quality shackles were the thread is mainly zinc.

4 Not taking the chain load on a snubber ..... or the snubber falling off ...... resulting in the windlass breaking, free-running, or being wrench off its mounts. Don't forget that the windlass is not designed to take anchoring loads ..... the gypsy shafts can and do break, and the worm gears strip.

5 Not making off the chain properly above the snubber. I always put another rope around the chain and made of to a cleat after my snubber (actually a bridle) chain-hook fell off the chain when the bridle touched bottom.

6 Electric windlasses contacts/switches shorting so that the electric motor runs up or down. This has happened on more than one occassion when I left the windlass breaker on. Once it happened on a friend's boat half way across the Atlantic. Before we managed to throw the breaker, half the chain was over the side.

7 The bitter end of the chain should always be attached to a strong point on the boat by at least 3m of substantial nylon rope. If the chain ever runs away out of control, the shock loading at the strong point could be enormous ..... the nylon would significantly reduce this. I was on one point a few years ago where the bitter end was made off to a saddle clamp held on with self tappers ......

8 Of course you should check you chain periodically too. The first and last 3m are usually the worst, and those between 30-50m due to gypsy wear.
 
How wold you ever get a snatch load on a chain used on an anchor? Surely to do that the chain would be lying on the sea bed the boat would have to move back and pull on the chain. The lifting of the chain off the sea bed would slow down the backwards movement so no acceleration, by the time the chain was tight between anchor and boat much of the force would have been reduced.
I'd love to be able to see it all happening, has it ever been filmed under water?
 
Spyro said:
How wold you ever get a snatch load on a chain used on an anchor? Surely to do that the chain would be lying on the sea bed the boat would have to move back and pull on the chain. The lifting of the chain off the sea bed would slow down the backwards movement so no acceleration, by the time the chain was tight between anchor and boat much of the force would have been reduced.
I'd love to be able to see it all happening, has it ever been filmed under water?
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Depends on depth and windspeed, but above a certain load the chain is straight, and wave action (and maybe yawing?) can then give the whole thing a shock.
 
Chain snatching

We had a definite snatch load on our chain a while ago. Anchored, dug in, caMe to retrieve in rising wind and the anchor had caught (I think in rocks?). Hauled up short with windlass until virtually straight up and down in F5-6 with a few miles of fetch and depth ca 12m. Pitching up and down about 1m at a guess at the stemhead. Horrendous sounding shockloads on the bow roller, and I was at the point of buoying the anchor when something gave. Fortunately it was the grip of whatever it was on the anchor, which came up.

I have renewed the roller/axle, chain, shackles and windlass since.

My point is that it can happen if the anchor gets caught.
 
Spyro said:
How wold you ever get a snatch load on a chain used on an anchor? Surely to do that the chain would be lying on the sea bed the boat would have to move back and pull on the chain. The lifting of the chain off the sea bed would slow down the backwards movement so no acceleration, by the time the chain was tight between anchor and boat much of the force would have been reduced.
I'd love to be able to see it all happening, has it ever been filmed under water?
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It can happen quite easily if you are unlucky enough for the chain, not the anchor, to foul something on the bottom. You can then get a straight up and down chain, and all it needs is for a big(ish)wave to come in, and bang! your chain breaks. Moral - don't anchor in foul ground.
 
Never broken a chain, but have broken an anchor - fortunately in benign conditions. It was a Sunsail CQR-look-alike, and the 'loop' at the back of the plough, where it swivels around the pin on the stock, broke clean through. The stock came back aboard with just 180º of the loop on the end of it and no plough. Judging by the crystalline appearance of the fractured loop, it was poorly cast, not well forged like a real CQR.
 
I have been supervising about 60 moorings at our club for the last 3 years. I have never seen a mooring chain break but we have had several boats go adrift. In each case it was a shackle failure. Any shackle left submerged for a long period is liable to corrosion of the pin threads which can let the pin fall out. Mousing with stainless steel wire prevents short term loosening of the pin but in the long term can cause higher rates of corrosion. One of our contractors used to weld the shackles closed but again the weld is subject to higher rates of corrosion and when that goes the pin falls out. Our present contractor rivets the end of the shackle pins by hammering the end of the thread.

Interestingly, every failure I have known has occurred in light conditions. presumably when boats are jiggling the pin about rather than applying a heavy load.
 
I have just taken delivery of a 40Kg Rocna for my 22 ton yacht. The Rocna site recoemmends a shackle with 16mm pin. It also features shackles made by GreenPin. The breaking strain of the GreenPin 16mm galvanised shackle is 2 tons. A 16mm stainless steel shackle has a breaking strain of 8 tons. Is 2 ton breaking strain enough??????

Tudorsailor
 
Two yachts were lost last October at West Kirby when the mooring chain of one parted in a F9. It then collided with the 2nd casualty and ripped it off its mooring, both ending up on rock armour sea defences. The club boatman said the trail of the broken chain was visible in the mud as they made their final passage Don't know the chain size but the 26' yacht had been kept on mooring for a few years and the ground tackle was lifted annually. The condition of both sets of remnants suggested that they were well maintained.
 
I should think it's mostly the undersized shackles that people use to attach the anchor to the chain that are likely to fail. Looking around a marina will show many examples of boats having an adequately sized anchor and chain with a puny shackle joining them; a built-in weak link.

I once crewed on a big steel ketch and the anchor got caught in some rocks. The skipper decided to try and break it out but the shackle gave way. For some reason he decided not to bother recovering the lost anchor and, as we sailed away, I noticed some people off a nearby German yacht jumping over the side and diving to recover it. They must have thought Xmas had come early!
 
When using a rope/chain rode, the winch gypsy is usually made for 14mm rope/8mm chain or (next size up) 16mm Rope/10mm chain. Now, to me, 8mm chain looks MUCH stronger than 14mm octoplat, although I beleive the theoretical breaking strain is similar. And I have actualy broken 14mm octoplat (mooring foul up). I think I would be happy on 16mm rope/8mm chain in most circumstance, saving some weight, but gypsies don't seem to allow it.

MD
 
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