G70 chain

[Neeves]

There is a thread over on Cruisers Forum on whether G40 or G70

http://www.cruisersforum.com/forums/f118/g70-chain-vs-g4-225019.html

G70 chain has had its ups and downs, mostly downs (due to galvanising quality) - but it does generate interest at least amongst a few of us - for those with no interest - move on, you might be bored!

What sparked part of my interest was an observation (sorry my usual long winded thread :

I think I have this right - but I stand to be corrected.

Commonly chain is sold based on size and the strength of wire from which the chain is made. G30 is made from a wire with a minimal tensile strength of 300 MPa and if you happen to buy a lifting chain then G100 chain is bought with a wire strength of 1,000 MPa (or it is that strength when processed - usually Quench and Tempered). G120 is a bit of an oddball as it seems to be a G100 wire but the link size is enhanced (square links as opposed to round links was the first divergence). The manipulation of link size results in a bigger cross sectional area - and stronger chain.

This coincidentally resulted in 8mm G30 chain having a minimum tensile strength of the chain of 3,000kg and G40 chain having an MTS of 4,000kg. If you note Vyv's tests - actual strength of G30 is near, but not quite, G40 and G40 meets G40, just.

G70 is an oddball - hence the interest.

The biggest and most well established manufacturer of galvanised G70 is Peerless (owned by Kito), through their ACCO plant. They make their leisure marine G70 from a G70 Transport chain that they galvanise. So - they make their chain, from a steel alloy (I don't recall if its a Boron of Bismuth addition to the alloy) similar to the alloy but not identical to their G43 (transport) chain and then Q&T it. This gives them their G70 transport chain. They then galvanise this chain and the heat of galvanising re-tempers the chain and it results in a chain with a strength of 'about' G55 (but they still call it G70).

Quench and tempering is a re-crystalisation process, under controlled cooling conditions (which are proprietary) and I assumer the Bismuth or Boron additions help the control of crystal growth. I also assume other processors might use different alloys or different levels of the same alloy addition to suit their re-crystalisation schedules). Re-heating, galvanising, modifies the original tempering but subsequent re-galvanising will leave the chain with a similar strength to that imparted when first galvanised - so -regalvanising of G70 is quite possible - producing a chain of similar characteristics as was originally installed in the yacht (confirmed by a chain maker and independent tests)

Maggi who entered the market more recently seem to base their chain on a G100 product, which is also Q&T, but when they galvanise they again retemper and the strength falls - but to result in their having a 'true' G70 chain.

So the Peerless 8mm product has a strength of about 5,500kg and the Maggi product has a strength of about 7,000kg. In comparison 8mm G40 chain would be a 4,000kg MTS. So Peerless is a real step above G40, Maggi is a great leap above G40.

There is then introduced a fiddle factor Peerless gal G70 has a safety factor of 3:1 and Maggi chain a safety factor of 5:1. resulting in WLL of 1,800kg and 1,400kg. I think in fact West Marine tend to emphasise the WLL, of Peerless G70, and leave the buyer to search for the MTS.

There is only one other manufacturer of G70, of which I am aware, Campbell also in America (part of Apex Tools) but they appear to have no real interest in leisure marine (though they do make to 'our' sizes but only imperial). Maggi and Peerless make both metric and imperial.

Metric chain sizes are 'simple' (apart from 10mm chain which has 2 size specifications) but each imperial chain type/quality has a different link size, so BBB is different to G30 and different to G43 and different to G70 - resulting in windlass makers having a huge range of gypsies. Some gypsies are forgiving of some types, apparently, but check and double check.

When people talk about buying G70, or there is a thread about G70, these contradictions are, completely, ignored.

Historically if you were to option to alter to G70 having used, in Europe or America, a G30 then the rule of thumb was to buy the next size down. This same rule of thumb has been applied to Maggi, since they entered the market, even though their MTS is much higher and their WLL much lower.

Makes little sense to me.

We wanted to downsize our rode, to save weight) and there was no 6mm 'high tensile' galvanised chain - so we had our own made such that the end product had the same strength as the 8mm (Grade L in Australia - but the same as G30) we had been using. We did not try to match the specification, or Minimum Tensile Strength but match the Ultimate Tensile Strength. The chain we had made - was cheaper than standard Australian or CMP Chinese G30 8mm chain. We have been using it for almost 3 years now - without issue (it took time and effort - but well worth it, if you want to save weight).

Jonathan

 

[Neeves]

Not everything you read on the internet is true and it does not get more true by constant repetition.....


As a number, 161, of people read, or looked and moved on , the initial post, or one person read it many times , I thought.....

Continuing my thread on G70....

A couple of posts on the thread, linked above, on CF were not challenged, Posts 6 and 16. Both were suggesting G70 chain would be more brittle that G30 and G40 (or G43 in America). This brittleness was mentioned as a reason not to use G70 chain.

There is no basis for this, in fact its...

wrong.

The NACM, an American association of chain makers have set specifications for chain and the minimum elongation for G80 and G100 chain is 20% and the minimum elongation for G30, 40 and 70 is 15%. In fact the Americans demand that their HT chains are less 'brittle' than G30, 40 and 70.

The NACM define elongation as the total extension, as a percentage, to fracture - this then includes any elasticity and any permanent deformation.

The contention that HT chains are more brittle than chain made from more mild steel is, in this case, fallacious. In fact the lower grades have less elongation to break than the higher tensile grades - the lower grades are more brittle than the higher grades.

However as outlined in the initial post, above, G70 is a re-tempered product and the NACM do not take account of this sort of variation. The NACO also only define specifications for the basic chain, no mention of galvanised grades.

If you care to look at this link

https://www.practical-sailor.com/issues/37_42/features/Looking-into-High-Test-Myth_11416-1.html

and look to the spreadsheet in the top right hand corner you will find test results on American chains, G30, 40 and 70 (+ Maggi) and the elongations of common chain from some suppliers.

The test data does not actually meet the specifications set - but you would find it difficult to distinguish the elongation between G70 and G30/G43.

G70 is as likely to fail, or not, as G30 of G43 - they are equally brittle, or not brittle.


Another fallacy is that you cannot regalvanise G70 chain. Based on advice from a chain maker, who said that regalvanising G70 chain was quite feasible I conducted some tests myself....

https://www.practical-sailor.com/issues/37_81/features/Regalvanizing-G70-Chain_12263-1.html

Whereas my tests are hardly conclusive it does reinforce what I was told.


Now nothing, really, to do with G70 chain:

Another interesting aspect that is contained in one, or a couple of, posts is that owners have experienced permanent deformation such that the chain would not fit in their gypsy. I would not challenge the information but 'normally' chain is Proof Tested at 2 x WLL (sometimes in America 1.5 times) - which basically means the chain will not deform (elongate permanently) under that tension. Equating that to metric chain - that means they have been subject to chain tensions (say 8mm chain) greater than 1.5t (PT at 2 times - which is the metric standard) or 1.125t (PT at 1.5 times) - chain tension developed from windage on the yacht.

I'm surprised that the ground tackle, bow roller, windlass etc survived that load and that the anchor held (unless of course they were using a good modern anchor - and there was no yawing, hobby horsing etc.).


If I get a quiet moment - I'll dig out more detail on other fallacies of G70 chain.

Jonathan

 

[Neeves]

No fallacies here

Installing G70, or a variation of, chain is not straight forward.

As Thinwater says - you need to ensure the windlass is rated for the task. Commonly you might use a 8mm G70 chain as a replacement for a 10mm G30 chain - the windlass would normally be supplied (assuming you are using the original windlass) for that chain - no problem (except you need to change the gypsy). However if you simply go off and buy a new windlass, because you consider the old windlass has outlasted its shelf life, then simply buying a new '8mm windlass' will mean the windlass might be underrated. if you are replacing 10mm chain with 8mm chain you need to buy a 10mm windlass with a 8mm gypsy.

The chain might be smaller but the loads are, mostly, still the same.

When we upgraded we discussed with both Muir and Maxwell. Muir were not very accomodating and Maxwell bent over backwards to understand and offer suggestions. We ended up with a Maxwell vertical windlass rated for 8mm chain, a 1000 watt motor and a 6mm gypsy (after 3 years no complaints, only praise).

Another issue raised by Thinwater, on a different thread, It is very difficult to add rope to a G70 chain as the links are so small you cannot splice a rope (long splice) of the required strength to the very small link size. You could extend the rode with some bigger links - but then it will not fit the windlass. We don't have rope on our main 75m rode but we galvanised an extra 15m of 6mm chain and used an Omega link as a large link and simply eye spliced extra rope rode (40m)

It is very difficult to find connectors, shackles, small enough for the new smaller sized G70 link, that fits the anchor and is stronger than the chain. One option is to have larger links welded to the end of the chain - but then you have links that have not been Proof Tested.

When we had our G80 chain 'made' (galvanised) we included Omega links (called 'connectors' by Crosby). Ours were from Van Beest in their Excel range and we optioned for G100 links. These links were also tested to ensure they were stronger than the chain. Really we are using them as enlarged links and attach the shackle to the Omega link. The clevis pin of these links is secured with hammer in pins and though they are reusable its a bit of a faff (you need to drill out the pins and hammer the clevis out with a punch).

Most components come painted and when you want them galvanised you need to remove the paint. Ideally you should source unpainted components but many manufacturers will not comply (the only ones we have found were Chinese). If the components are painted we found grit blasting not very successful (the components are powder coated rather than painted and the coating is robust) we used 3 applications of paint stripper and a wire brush - its a messy job. We also processed extra components, Omega links, hooks etc so we carry spares.

We have a Boomerang in our rode - the original design of which was to accept appropriately sized shackles - we made a new Boomerang to accept Omega links. Our 'hook' for our bridle is also custom made and we use off the shelf 6mm hooks from the lifting industry, again galvanised, as our back up snubber and to secure the anchor when on passage.

If you speak to a galvaniser many will be sympathetic and will work with you. Nothing should be pickled, acid washed (it is the root cause of hydrogen embrittlement) everything should be grit blasted - best done in house, or cleaned and galvanised within hours (not the next day).

Why Peerless (or West Marine) think they can sell G70 chain without matching components is a bit of a mystery. Maggi did address this issue with Omega links from Rud - but the links were huge and will detract from anchor performance.

If you option G70 you need to search for all the components you think you might need yourself - chandlers (and the chain suppliers) have little idea.

Jonathan

More later.

 

[Neeves]

The usual reason to use G70 chain is to reduce weight and the weight savings are considerable - if you have 100m of rode the savings, by down sizing from, say 10mm to 8mm, are easily that of someone standing permanently on the bow (and then taking them away).

Would you want to sail to windward with a man on the bow.

You not only save weight but you also save space in your chain locker, not that it is easy to use the space, but there is a chance towering of the chain, when you retrieve, becomes less of an issue.

However the savings mean the rode is lighter and strangely of all the, 'few'?, people who use G70 - none of them highlight the loss of catenary as being an issue (possibly because they all use decent snubbers).

There is a phurphy that G70 wears more because it is, commonly, a smaller link. Oddly if this had any truth I am sure we would see more complaints from the Americans - but it is simply not mentioned - at all. It would be interesting to see any justification for the comment - I have done some tests and can find no basis for the comment (internet trolling at its best). In Europe Maggi's G70 does have this reputation for poor galvanising, but then so does Maggi's G4 - yet Peerless G7 seems problem free.

One conclusion might be - Maggi's galvanising is, was, at fault.

G7 chain does not gain much traction and the users are limited, or they seldom post on internet forum. Usage is thus difficult to define.

Jonathan