Catenary - would you buy krypton piano wire?

[JumbleDuck]

Yes, intentionally thick, since I believe you know these things, but I will forge ahead anyway:
- Dyneema floats. It will be all around your rudder and keel.

OK, reasonable point, despite the disappointing and quite unnecessary personal abuse. Some sinking rope instead, then, or weigh down the dyneema like other weighted lines.

- G100 chain is a little less then 1/2 the weight of standard chain, but it is STILL 1/2 the weight of standard chain. Cattenary is less, though not if you deploy just a little more (then it is better per weight).

There is stuff-all catenary effect even with normal chain.

- Chain is effectively cut proof. Dyneema is somewhat resistant, but 12-strand is really not very good side to side on rock

Which is why I suggested some chain at the bottom end.

It's complicated. The question he asks, put another way, might be "when is chain too light?"

He asked if we ourselves would use super-strong super-light chain and I explained why I would not.

 

[RupertW]

Sorry, not getting your point.

Are we agreed that (a) chain has very little stretch and that therefore (b) any "elasticity" in chain comes from gravity effects, aka catenary and (c) the effectiveness of this reduces as chain mass/length decreases?

In which case, using a very light chain loses all the benefits of chain (save that the bit on the bottom still has chafe resistance) while gaining none of the benefits of an elastic rope. I think Neeves recognises this with his reference to "krypton piano wire". The end point of making a chain lighter while keeping its strength is, basically, something with the same properties as dyneema. So why not go straight there?

Agreed that elasticity in chain come from catenery but that is irrelevant in any real scenario as it diminishes to such a tiny bit of elasticity in any breeze (see that helpful graph in the other thread) that catenary can be dismissed as a pretty low wind effect unless you were a 22 footer with 19mm chain and lots of it. However as you say for precisely that reason dyneema has very similar properties except for the floating issue so I think you are right to say that for both chain and dyneema you need to add a similarly stretchy element to the rode to reduce shock loads.

I don't think my solution is perfect but I use a rubber snubber on a nylon rode attached to the chain by a hook. So up to maybe 20-25 knots and a short scope a 2m nylon rope with rubber thing is fine (I usually anchor at 3:1 in a crowded anchorage but more if I have room), then if the wind conditions get up I gradually release more nylon rode up to (in theory) 60m, expecting the rubber snubber to be stretched beyond use and needing replacing if it blows a hoolie.

For my 12.5m boat the 10mm will be replaced by 8 (or 6mm if they ever made it strong enough) when I can next afford it. My only problem with infinitely strong light (as long as it sinks) piano wire is chafe.

 

[Neeves]

Where do you get a shackle that will join 6mm chain to the anchor while being of a strength to match the HT chain?

This is the easy part.

G100 chain is part of a portfolio of attachments, all different shapes and sizes to meet every conceivable application. One of these is a device called an Omega link (but there are others hammerlocks being one). These are made to match the chain for both size and strength.

The previous idea was you have enlarged links attached to your HT chain (G70), this was an extra, significant, cost, you were not entirely sure how good the welds were, it was difficult to galvanise the end links. With an Omega link you simply attach a custom made enlarged link and the shackle (sized for the anchor, even if the anchor is overly large) will fit the Omega. The Omega's are actually much stronger than the chain, under test, and would be galvanised at the same time. To elaborate - when the, proposed, chain is tested for elongation and strength Omega links need to be attached to the ends of the chain to provide a link big enough to attach the tension equipment. The Omegas are of 'matching' strength (because there is nothing convenient and cheap that is stronger. When the chain fails the clevis of the Omega has distorted slightly - so the Omegas are much stronger than the chain. Matching Omegas are a bit larger than the chain link size but a bit smaller than the shackle.

You could use hammerlocks, similar story - but the clevis pin is thinner and might be subject to abrasion.

As with shackles - any of these devices will corrode, because they are in contact with metal of a different chemistry - when they look unsightly, cut them off and attach another. Omega links will cost the same as a decent shackle.

As well as Omega links the portfolio of attchments also cover chain hooks, of countless designs (maybe 100). These are also made to match the link size, physically and for strength. Attaching a snubber, or bridle is there fore easy - again they would be galvanised with the chain.

The idea being you would buy chain, omega links (+ spares) and hooks (plus a spare) all matching, all certificated for strength, elongation and galvanising coating thickness. You would need to supply the snubber itself and appropriate shackles (Crosby and Campbell being the best, or only ones easily available).


And to allay suggestions - I'm in no way trying to sell chain - I am interested in why people would or would not use it. Many are not convinced about the virtues of catenary - if push came to shove - how firm are those convictions - or is it talk and there is insufficient data to counter fears.

Jonathan

 

[thinwater]

With G100 chain we should not be assuming it is completely non-stretch. In fact, at equivalent portion of working load, it has about 1/4 the stretch of nylon and similar stretch to polyester. Look up the specs, do the math. See if I am wrong (remember that WLL for chain is ~ 25%BS but only 12% WLL for nylon. How can this be? High strength steel is stronger than mild steel, but it is not stiffer, thus it bends more without yielding. Remember that nylon rope only stretches about 5% at its WLL. Load it harder than that and it will fatigue.

- This is why it makes better binder chain for a lorry; it stretches just a little.
- This probably compensates for some of the loss in catenary. Sounds like time for testing.

 

[Neeves]

For my 12.5m boat the 10mm will be replaced by 8 (or 6mm if they ever made it strong enough) when I can next afford it. My only problem with infinitely strong light (as long as it sinks) piano wire is chafe.

The 6mm would be strong enough.

One of the characteristics of High Tensile steels is that they are hard, more abrasion resistant, than mild steels. During production of HT steel plate - hardness is one of the QC tests during process as it can be done quickly and instantly determines if it will meet UTS. UTS need wait till the steel is completed, samples cut etc - hardness can be done with a punch on the edge of the steel. One application of HT steels is in mining where they are used a as bed, over which rocks move, or as teeth on diggers. HT steel chains have the same characteristic - though it is not part of specification - because normally it is not important.

One application of the galvanising process for the US Marines was to have access to a more abrasion resistant galvanised coating - they achieved their objective and are using the process envisaged.

Independent abrasion tests I have seen and tests I conducted confirm this. The US have set a galvanising coating thickness of 80 microns, the thickness of the coating on my chain and subsequent has been 100 microns.

The unknown is - how does 6mm (or 8mm) G100 compare with the product to replaced Hot Dipped Galvanised 10mm G30/G40 for abrasion resistance and abrasion resistance of the underlying steel. So - a comparison of different processes and different sizes (now for both the coating and the chain) This is one comparison that needs to be completed.

Accepting this omission, but assuming it is positively resolved, do members consider the small HT chain sensible, for specific environments/yachts - or are the subjective fears too much to resolve?

Jonathan

 

[JumbleDuck]

With G100 chain we should not be assuming it is completely non-stretch. In fact, at equivalent portion of working load, it has about 1/4 the stretch of nylon and similar stretch to polyester. Look up the specs, do the math. See if I am wrong (remember that WLL for chain is ~ 25%BS but only 12% WLL for nylon. ...

Much of that WLL will be plastic strain and non-recoverable, will it not? Have you a link to a stress-strain diagram for the steel you have in mind?

 

[JumbleDuck]

Accepting this omission, but assuming it is positively resolved, do members consider the small HT chain sensible, for specific environments/yachts - or are the subjective fears too much to resolve?

You do yourself no favours by characterising any resistance to your sales pitch as "subjective fears".

 

[Neeves]

You do yourself no favours by characterising any resistance to your sales pitch as "subjective fears".

Maybe you did not read all the posts

I'm not selling chain.

I'm exploring motivations, or not

Jonathan

 

[JumbleDuck]

Maybe you did not read all the posts

I'm not selling chain.

In a metaphorical sense ("selling an argument") you are, really, just as you have previously tried to sell us G40 chain, G60 chain, chain with every link tested and about three new galvanising processes to date as well as new generation anchors. Commendable enthusiasm, but is it based on any real needs? Most of us have anchors which work well enough for our purposes.

I'm exploring motivations, or not

Perhaps better not to discard any motivations with which you do not agree as "subjective fears" a priori, then?

 

[RupertW]

In a metaphorical sense ("selling an argument") you are, really, just as you have previously tried to sell us G40 chain, G60 chain, chain with every link tested and about three new galvanising processes to date as well as new generation anchors. Commendable enthusiasm, but is it based on any real needs? Most of us have anchors which work well enough for our purposes.



Perhaps better not to discard any motivations with which you do not agree as "subjective fears" a priori, then?

I'm objectively convinced (both by the maths and practical observation of high winds in clear water) of the lack of merit of weight in chain, as long as it sinks. I'm also highly intrigued by the new stronger smaller chains available but I do have subjective concerns about chafe and therefore corrosion after degalvanising. Where I do agree with Jonathan is that these remain subjective until there is evidence that a 5 year old HT 6mm chain will hold up as well as a 5 year old 10mm chain to general abrasion.

The advantages of extra chain fitting into the same space up forward are a big deal for me and much easier to handle than adding my 60m rope rode to the 60m of 10mm chain. (Well alright 15 seconds quicker in daylight but in the dark with fumbling it might add a lot more time as there is no room to keep the rope permanently attached to the chain.

 

[zoidberg]

There's just a hint of an 'ad hominem' sneer creeping in - an element of 'playing the man, not the ball' for those Jockinese without Latin - and that contributes nothing I find useful to the discussion. Something of the 'New Progressive' intolerance, and I reject that....

I'm always interested in fresh thinking, new ideas, better ways. No good idea is born fully formed. It always needs polishing, and here is a good place to exchange caveats about boating gear and practices, in a spirit of courteous questioning.

I'd use 6mm G100 chain, if it did the job and I could afford it. I'll look up the Omega link info, too. I could use a couple of those....

 

[Neeves]

JD you can be highly imaginative.

I have never tried to suggest anyone buy G40 chain (if you are interested Jimmy Green sell it - its apparently commonplace, there must be a real need), I have never suggested anyone buy G60 chain (it does exist but I'm not sure in short link sizes and I'm not sure that it is galvanised). Most chain has every link tested - its standard practice. I have never described 3 galvanising processes. This thread does not mention anchors - but there is a need for new generation anchors - lots on this forum buy them.

Your lack of accuracy does you no credit.

And in case you have missed it some people have been positive and made positive comment. You would rather they be denied access to ideas and and an ability comment?

You will not mind if in the future I simply ignore your posts unless they are accurate, constructive or enjoy the benefit of your undoubtedly considerable academic knowledge as this latter would be of benefit to all.

An alternative might be to transfer your objections to the The Lounge.

Jonathan

Edit The posts from RupertW and Zoidberg crossed with mine, which went through a number of revisions, and in the end did not reflect what I wanted to say. close Edit

 

[Roberto]

I have to replace my 10mm chain (regular, g30-g40 or whatever), the worst corroded links have dropped to 7mm. I considered 8mm G70 but not being able to find if there is any difference in corrosion rates between the two type of metals -I doubt that can be significant, and I am not willing to buy G70 just to check if it is the case- I'll buy 10mm again.
The loss of 1mm of G70 means a lot more strength is lost compared to the same amount of g30-40. Also, sometimes I am away for months from places where one can buy chain, let alone galvanise it, so I prefer a sort of buffer "excess diameter" , if excess it is.
In some waters, possibly acidic (?), galvanising has been taken off quite rapidly.

Fwiw, I have made some comparisons with catenary formula:
Depth (davit / sea bottom) 5m
With 25m 10mm chain (scope 5:1) the horizontal force on the boat to lift the last link of chain (catenary tangent to the sea bottom), is about 122daN; chain weight 60daN
To get an equal 122daN force with 6mm chain, 41m are needed (scope about 8), total weight 35daN.


Re Maggi, these days' news is they have asked for legal administration (?, not sure of the correct English term): they have asked a judge to arrange a meeting with creditors in order to try and avoid insolvency, either by restructuring/layoffs/asset sales etc, or possibly liquidation.
https://www.lecconotizie.com/econom...atene-chiede-il-concordato-preventivo-431113/

 

[Neeves]

Roberto

Your maths does you credit.

It puts numbers to a suggestion that Thinwater made in one of his posts.

There is no suggestion that 6mm chain would be used alone. It would be used with a snubber, nylon, to replace the catenary that has been 'sacrificed' to save the weight and volume. The length of the snubber would be variable, shorter in lighter winds and longer in stronger wind. But it would be skinny - so as to have elasticity.

This does not invalidate your maths - just makes it more complex to complete a calculation.


You news on Maggi is disappointing as it may leave only one supplier of galvanised G70 chain.

Jonathan

 

[RupertW]

Roberto

Your maths does you credit.

It puts numbers to a suggestion that Thinwater made in one of his posts.

There is no suggestion that 6mm chain would be used alone. It would be used with a snubber, nylon, to replace the catenary that has been 'sacrificed' to save the weight and volume. The length of the snubber would be variable, shorter in lighter winds and longer in stronger wind. But it would be skinny - so as to have elasticity.

This does not invalidate your maths - just makes it more complex to complete a calculation.


You news on Maggi is disappointing as it may leave only one supplier of galvanised G70 chain.

Jonathan

I think both of you are falling into the fallacy of good equations but wrong assumptions (in my view) re catenery as the difference in catenery between 6mm and 10mm is very small in the kind of wind forces where it matters. The assumption which I think is incorrect is ever looking at the need to keep any chain on the bottom - ie. 0 degrees to the horizontal. Once you accept that even CQRs can cope with 10-15 degrees and keep digging and Rocnas nearly double that then you realise that scope is king of setting a good angle, not weight of chain and catenery (which of course exists, is proportioanal to chain weight etc etc ... I completely agree with the maths but with my assumptions it leads me to a different conclusion).

 

[noelex]

As you go to thinner chain the greater movement an abrasion on the bottom is very obvious underwater, and I think this biggest factor contributing to the earlier demise of thinner high tensile chain.

The loss of 1mm of G70 means a lot more strength is lost compared to the same amount of g30-40.

I think this an important point that should be understood by anyone moving to the higher tensile chains.
If I understand correctly G7 "High tensile" chain is produced by creating a compression layer on the outside surface of the chain. The loss of, for example 1mm in diameter of 8mm chain is obviously more significant than the loss of 1mm on 10mm chain, but unfortunately in G7 chain it is the outer layers that are in compression. Therefore the loss of these outer layers caused by corrosion will have a very significant impact on chain strength. If the outer high compression layers are lost the chain effectively looses its high tensile properties.

For these reasons I think we need some caution with high tensile chain. It should be replaced at the earliest sign of corrosion. Given the advantages of significantly lighter weight G7 and G7+ chain is still a great option for boats where chain weight is critical, but I don't think it is the global panacea that is suggested.

 

[thinwater]

Much of that WLL will be plastic strain and non-recoverable, will it not? Have you a link to a stress-strain diagram for the steel you have in mind?

No plastic strain below the WLL. That is a definition.

You can Google welded chain standards.

 

[thinwater]

As you go to thinner chain the greater movement an abrasion on the bottom is very obvious underwater, and I think this biggest factor contributing to the earlier demise of thinner high tensile chain.



I think this an important point that should be understood by anyone moving to the higher tensile chains.
If I understand correctly G7 "High tensile" chain is produced by creating a compression layer on the outside surface of the chain. The loss of, for example 1mm in diameter of 8mm chain is obviously more significant than the loss of 1mm on 10mm chain, but unfortunately in G7 chain it is the outer layers that are in compression. Therefore the loss of these outer layers caused by corrosion will have a very significant impact on chain strength. If the outer high compression layers are lost the chain effectively looses its high tensile properties.

For these reasons I think we need some caution with high tensile chain. It should be replaced at the earliest sign of corrosion. Given the advantages of significantly lighter weight G7 and G7+ chain is still a great option for boats where chain weight is critical, but I don't think it is the global panacea that is suggested.

I understand the words, but rather than argue each point, binder chain grade 70 or higher, why is lifting chain grade 80 and higher, and why is lower grade chain forbidden? You can Goggle it. Basically it comes down to much greater wear resistance and toughness, the opposite of what is commonly believed. Where this belief comes from, I have no idea, but I would be glad to see the numbers.

 

[noelex]

why is lifting chain grade 80 and higher, and why is lower grade chain forbidden? You can Goggle it.

I don't think any of the factors that I have mentioned are relevant to lifting chain. There is no corrosion caused by immersion in salt water, nor any increased abrasion caused by thinner chain moving more on the seabed. There is not the same benefit from catenary when using heavier chain in the lifting industry.

If you want to look at a heavily regulated commercial application as an example of best practice for recreational vessels to follow I would suggest that the type of anchor chain used on commercial ships would be more relevant than lifting chain.

I understand commercial ships rarely (never?) use G7 or G7+ chain. Our requirements are different to commercial ships (and very different to the requirements for lifting chain) so personally I think extrapolating from these other applications is of limited relevance, but if you want to copy industry, using the best examples, the data does not support the use of G7 or G7+ chain.

I think we should decide for ourselves, based on our requirements, which type of chain is optimum. Duplicating the type of chain used in the lifting industry, or the very different type of chain used on large ships is not the answer.

 

[thinwater]

Any of the factors? That was casual.

Corrosion I do not know. We seem to have no evidence either way. However, there is one slight falicy in your reasoning. Though sailors typically down size when going to higher grade, they generally still end up with a greater safety factor. They go from G30 to G70, but only drop from 10 mm to 8 mm. Material strength increased 2.3x, but cross section decreased only 1.6x. The chain is much stronger to start with. If you go to 6mm, that is another matter.

Abrasion and abuse in trucking, logging, and industry is a huge factor. I think you will loose that one.

You have also ignored toughness. A high grade chain can absorb nearly three times as much energy without damage. It's in the specs. And chain does NOT fail from pure tension, it fails from snatch loads. This is why low grade chain is forbidden in lifting. Why do you think low grade chain is forbidden for lifting, and why does this mystery "factor" not apply to boats?

Commercial ships are less closely related than you imagine. First, the cost penalty per pound goes away. Since that is the entire basis of the argument, that should settle it. Second, fabrication methods change in larger sizes. For example, high strength steels are common in smaller tanks (compressors etc.) but when you get to larger sizes (millions of gallons) the grade of steel is slightly reduced, because the requirements for stress relief and fabrication become uneconomical. It is all about $/gallon of tank and weight does not matter. Finally, how many recreational boats are made from steel? There are many reasons, but I only make the point that this demonstrates how unrelated they are.

We're just going to have to disagree.