Anchor chain stretch?

[Compass790]

Originally Posted by sdj

Try towing a car with a chain and you will get your answer. Don't try this with a car you want to keep.

Chains don't stretch.

If you are in Auckland go to chain & rigging in Penrose & tell them that. If you are lucky they might show you their chain testing machine & some stretched chain.
Then you can come back on this thread & tell us what you saw or better still take photos.

[thinwater]

Originally Posted by Simi 60

From this site
https://twoatsea.com/anchor-chain-information-resource/





For us in the 80 it was a in behind a low island so not much wave action nor protection from wind for us, but it was a E N/E at 20 and then W N/W at 80.
We noticeably went backwards, veered and leaned over a fair bit, water was coming through windows (since removed and sealed properly) horizontal hail, almost zero vis, sounder lost bottom, GPS lost signal, Radar showed nothing, depth and drag alarms shrieking.
Occasionally we would see a boat drag past.

When it finished and we got GPS back, we were probably the only boat out of about 20 who hadn't moved.

We had moved out about an hour prior when it became obvious we were in line and put 14 ft under our 7ft draft and ran out 150ft for 5:1 (14+7+10 to the deck) of 13mm chain attached to a 150lb manson supreme.
Snubber at the time was 10ft of 1 inch silver rope, so no real stretch.
Since replaced with 20ft of 3/4 inch nylon.

Damage done apart from deformed chain was step treads going from the sides to the foredeck , about 2ft x 1ft x 2inch made of merbau and very heavy that had been held down by gravity had been sucked up and deposited about 10ft fwd on the deck punching holes through the fiberglass skin.
Horizontal hail had found some undiscovered rot in the ply bulwarks and it looked like it was shotgun blasted.
In its path it had blown shipping containers around at the Port and moved passenger jets around at the airport.

Next time well run out more chain.
It does nothing for you sitting in the locker.

ABYC H-40 gives the WLL for a storm (which was formerly identified as 42 knots) as 4000 pounds and 6000 pounds for moorings (60 knots). 80 knots is about 3.6 times that of 42 knots. We know ABYC is ~ 4x conservative in normal circumstances, but with no snubber, no catenary, and a lot of yawing (that can increase the rode tension 50-100%) the force was probably 100% of that, which is 4000 x 3.6 x 1 = 14,400 pounds. WAG. That's well above the WLL of the chain (4500 pounds) and enough to stretch it. It will eventually fail at that load due to fatigue.



The chain is simply too small for severe conditions. Big, heavy boat needs big chain. Or much higher grade. Or some of both. It's a lot of boat.

[Simi 60]

Originally Posted by thinwater

ABYC H-40 gives the WLL for a storm (which was formerly identified as 42 knots) as 4000 pounds and 6000 pounds for moorings (60 knots). 80 knots is about 3.6 times that of 42 knots. We know ABYC is ~ 4x conservative in normal circumstances, but with no snubber, no catenary, and a lot of yawing (that can increase the rode tension 50-100%) the force was probably 100% of that, which is 4000 x 3.6 x 1 = 14,400 pounds. WAG. That's well above the WLL of the chain (4500 pounds) and enough to stretch it. It will eventually fail at that load due to fatigue.



The chain is simply too small for severe conditions. Big, heavy boat needs big chain. Or much higher grade. Or some of both. It's a lot of boat.

Which gets us back to this post

http://www.cruisersforum.com/forums/...wo-225808.html

I am not wanting to drop $10,000 or more on new windlass and associated work for something that would most likely be remedied with running out more chain and nylon snubber.

[GordMay]

Elasticity vs Stretchiness:
The fundamental difference between a definition in physics, and a definition in common life, should always be kept in mind when one speaks of "elasticity".
In common usage, we label a substance as more elastic, if it can be stretched or deformed more than others, without breaking it.
In physics, a substance is labeled more elastic if it offers greater resistance to deformation than other bodies, so that it can be stretched or deformed less than others, without breaking it. The property of materials to yield to deforming forces, only to come back to the normal shape after the forces are removed, is called "elasticity".
Hence, steel (for instance) is fairly elastic, but not very stretchy.

[conachair]

Originally Posted by GordMay

The property of materials to yield to deforming forces, only to come back to the normal shape after the forces are removed, is called "elasticity".

"yield', in this context, might not be the best choice of word though...

The yield point is the point on a stress-strain curve that indicates the limit of elastic behavior and the beginning plastic behavior. Yield strength or yield stress is the material property defined as the stress at which a material begins to deform plastically whereas yield point is the point where nonlinear (elastic + plastic) deformation begins. Prior to the yield point, the material will deform elastically and will return to its original shape when the applied stress is removed. Once the yield point is passed, some fraction of the deformation will be permanent and non-reversible.

https://en.wikipedia.org/wiki/Yield_(engineering)

[a64pilot]

I have always understood elasticity to mean among other things that it will return to the exact same dimension, rubber for example is very stretchy, but it doesn’t return to the same dimension once stretched, so therefore it’s not real elastic.
It’s also the explanation of why a steel ball bearing or hammer will bounce so well, it’s returning to its original dimension.
The ability to return to its original dimension is also I believe why steel makes such good Springs, valve springs for instance, how many millions of cycles does one of those get in say 10,000 hours of operation?
https://www.dictionary.com/browse/elasticity

[BigBeakie]

As a datapoint, I can say from doing multiple break testing on our 8mm G100 Armorgal chain that at break, which is 8 Tons, the links were between 23% and 25% longer. The bend radius and the link wire diameter both changed. So in this case at least, high tensile chain is not necessarily brittle, as has been claimed.

The break strength of the non galvanised chain stock was about 15% higher than the galvanized chain.


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[a64pilot]

No, G100 chain, and indeed all chain approved for overhead lifting must not be brittle, there is a requirement for it to deform before breaking giving in theory a warning it’s about to break.
You can have strong and ductile if I’m using the word correctly by using a different metal, but if the metal is the same and you gain strength by heat treatment is pretty much a given that the metal becomes more brittle.
A common file is a good example, very hard and strong, but don’t try to bend one.

[evm1024]

Originally Posted by BigBeakie

As a datapoint, I can say from doing multiple break testing on our 8mm G100 Armorgal chain that at break, which is 8 Tons, the links were between 23% and 25% longer. The bend radius and the link wire diameter both changed. So in this case at least, high tensile chain is not necessarily brittle, as has been claimed.

The break strength of the non galvanised chain stock was about 15% higher than the galvanized chain.


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An interesting datapoint to add to the conversation.

Do you happen to know the percentage elongation at, or just before the yield strength?

Any chain that is stressed over the yield strength has failed (by definition) with permanent elongation. If not actually necking down at that point at least the steel has work hardened and become more brittle.

(or so I think)

[thinwater]

From the welded chain standard. Elongation referred to is elongation to break.





5.3.4 Elongation shall not be less than 20% for Grades 80 and 100; 15% for Grades 30, 43, 70, and Stainless; and 10% for Machine, Coil, and Passing Link chain.

[evm1024]

Originally Posted by thinwater

From the welded chain standard. Elongation referred to is elongation to break.





5.3.4 Elongation shall not be less than 20% for Grades 80 and 100; 15% for Grades 30, 43, 70, and Stainless; and 10% for Machine, Coil, and Passing Link chain.

Thanks, yes - knew that.

I thought that the original posters thought was along the lines of the "shock absorption" properties of chain stretching. FWIW....

I'm pretty sure that any chain that has links that have permanently elongated by 10% will not run very well through the windlass.

In my own case I have a wildcat that is sized for 3/8" BBB (link length of 1.105"). The PO had 5/16" HT (link length of 1.017 or 8 %short) which would not feed well at all. I am running 5/16" G70 (link length of 1.122" or 1.5" longer) which feels flawlessly.

I did try a short length of 3/8" G43 (link 11.3% longer than 3/8" BBB) which did not feed well.

[a64pilot]

When you stretch chain like I have many times on the farm, once stretched you can hold it out pretty much straight like a rod, it certainly won’t lay into a pile, and this is just common chain nothing high end like chain approved for overhead lifting.
Obviously chain approved for overhead lifting is manufactured to higher standards and inspection etc.

[BigBeakie]

Evm1020,

No sorry I do not have that data.

And I was not about to hop into the hydraulic ram testbed apparatus to whip out my calipers with the chain under that load either!😂

It sure was scary when it breaks at 8,0000 kgf., I can tell you that.

IMHO, this is an academic question, the issue of chain stretch to absorb anchoring forces. Just use adequate materials for a snubber and be done with it.


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[evm1024]

Originally Posted by BigBeakie

Evm1020,

No sorry I do not have that data.

And I was not about to hop into the hydraulic ram testbed apparatus to whip out my calipers with the chain under that load either!😂

It sure was scary when it breaks at 8,0000 kgf., I can tell you that.

IMHO, this is an academic question, the issue of chain stretch to absorb anchoring forces. Just use adequate materials for a snubber and be done with it.


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What, What! Not gonna jump on it? I fully understand. I've seen a few thing come apart and can understand why you would not want to go measure when loaded.

Agreed, it is academic but it would put to rest the thought that elastic deformation of the chain contributes significantly to shock absorption. Especially when contrasted to the that of a snubber.

Some points are Moot (1. subject to debate, dispute, or uncertainty.)

other points are Moot (2. having little or no practical relevance)