Anchor Chain For Extended Use In UK

CaptainBob

CaptainBob

Well-Known Member
Joined
7 Nov 2007
Messages
1,477
Location
North Yorkshire
www.yacht-forum.co.uk
Our boat is big and heavy (38 foot, 13 ton, ketch) and apparently (according to various websites) really ought to have 10mm anchor chain on it rather than the 8mm it has (which is now rusting), but I prefer to have 8mm as it's smaller, lighter and hence I can stow more of it, and hoist it by hand which is way quicker than with our manual winch.

If we had 8mm Grade 70 galvanised or Grade 50 316 stainless steel it would be (I believe) plenty strong enough and avoid the upgrade to 10mm.

But we anchor rather a lot, for extended periods of time, so I'm concerned about crevice corrosion in stainless chain... and the price makes me weak at the knees anyway.

But I hear that Grade 70 galvanised is not actually much better than Grade 30 as the galvanisation process reduces the strength of the chain anyway.

Or do you think we'd be fine with plain old 8mm Grade 30?

Thoughts?

TY!
 
CaptainBob said:
But we anchor rather a lot, for extended periods of time, so I'm concerned about crevice corrosion in stainless chain... and the price makes me weak at the knees anyway.

But I hear that Grade 70 galvanised is not actually much better than Grade 30 as the galvanisation process reduces the strength of the chain anyway.

Or do you think we'd be fine with plain old 8mm Grade 30?
Click to expand...

1. Crevice corrosion is highly unlikely in chain that is used regularly. If you stowed it under water and didn't touch it for a few years it might happen, but not otherwise. Provided it is well made and has no cracks in the welds or porosity in the wire, so careful inspection is required before purchase.

2. Grade 70 galvanised chain is considerably stronger than Grade 30, well over twice the strength in fact. There are concerns about regalvanising Grade 70 because the pickling process may lead to hydrogen cracking in the metal. However, this seems to be one of those worst case scenarios and may not actually happen. Also, it is said that Grade 70 can be regalvanised twice before it becomes an issue, which technically speaking makes no sense. Paul and Rachel Chandler fitted out Lorne Rival with Grade 70 from Maggi (Italy) before relaunching their cruising career.

3. My research and testing for YM found that much of the Grade 30 chain on sale in UK actually conforms to Grade 40 strength. Chinese made chain is now the best in the world and buying from an importer such as Bainbridge, Bradney, William Hackett and others will give you excellent performance at lowest cost. My only concern is that the galvanising may only last three or four years, but regalvanising is possible at about 1/4 the cost of buying new.
 
CaptainBob said:
Our boat is big and heavy (38 foot, 13 ton, ketch) and apparently (according to various websites) really ought to have 10mm anchor chain on it rather than the 8mm it has (which is now rusting), but I prefer to have 8mm as it's smaller, lighter and hence I can stow more of it, and hoist it by hand which is way quicker than with our manual winch.

If we had 8mm Grade 70 galvanised or Grade 50 316 stainless steel it would be (I believe) plenty strong enough and avoid the upgrade to 10mm.

But we anchor rather a lot, for extended periods of time, so I'm concerned about crevice corrosion in stainless chain... and the price makes me weak at the knees anyway.

But I hear that Grade 70 galvanised is not actually much better than Grade 30 as the galvanisation process reduces the strength of the chain anyway.

Or do you think we'd be fine with plain old 8mm Grade 30?

Thoughts?

TY!
Click to expand...


You will also extend the life of the chain and certainly reduce re galvanising cost with basic maintenance by washing out the chain with fresh water and leaving it on deck to dry in the sun , mine was replaced (10mm) 3 summers ago and barely has any rust staining.

Putting it straight into the locker salty and wet will reduce the life of the galvanising and ultimately the chain it's self massively.
 
Thanks for the replies. I suspect we've brought on rusting earlier than we might have, because we have indeed just left it in the locker, covered in seawater, all winter last year.

Had a quote for 316 Grade 50. Yikes!

Trying to find a trustworthy UK source of grade 70 galvanised...
 
I think you will need stick with Vyv's comments as Maggi seem to be only supplier of short link G70 in Europe. In Oz we have a product called Grade P, which is a galvanised Grade 50. I am not aware of it being made anywhere else but cannot think we are unique - you could try to look at sourcing it in Europe.

Vyv's investigation of G30 suggests much of what he tested, all from China I recall, is almost as good as G40. One has to wonder if G40 is equally better, and near G50? Maggi also make a G40, as do other Europeans. If you were concerned about strength and find stainless G50 a bit wallet crunching it might merit looking at defining actual strengths of G40 - Chains, Ropes and Anchors in NZ have some interesting test data (which might include G40 - as I know they have tested Maggi G70).

Peerless in America make a gal G70 under their ACCO brand (only available through West Marine) but its imperial sizing (and link sizes will almost definitely not fit a metric gypsy). New gypsies can be surprisingly expensive if you decided to go to 10mm (and the 2 metric specification for chain link size differ for 10mm (Vyv has the detail). CMP (of Rocna fame) make a short link gal G43 in metric sizing under their Titan brand, not sure if its available in the UK - but watch, they quote WLL (not breaking load) and G43 has a 3:1 safety factor not the 4:1 of G30, G50 and G70 - and as far as I can see G43 is as safe, or unsafe, as any other chain.

Interestingly cases of chain failure (breaking) are rare, in fact chains from reputable suppliers do not seem to fail (or not as a result of being weak)- everything else fails, shackles, swivels, anchors (they drag and/or bend) even bow rollers bend - but chain failure is notable by its absence (including these threads). I do not recall of even undersized chain failing. It might lose galvanising - but it does not break. I am sure there will now be a rash of chain failure stories!

Good luck - I for one would be interested in your final choice.

Jonathan

Edit: I'd try to buy Proof Tested chain (especially if its AISI 316 G50) if you can - it should have then been tested to approximately twice the Working Load Limit or half the breaking load. And if you use chain and get anywhere near a load of WLL you are either in a full blown hurricane (or not using a nylon snubber of 10m length).

As an aside, I'm in the process of replacing my 8mm G30 with 6mm G70 - so I have similar issues.
 
Last edited:
I think your 8mm chain is ok for your boat.

If your going to change anyway, you might want to go for 8mm G4 from the reputable suppliers mentioned by Vyv. Otherwise, keep what you have, re-galvanise if you think it needs it.
 
Have to concur with Vyv's comments.
High grade chain in galvanizing can be subject to hydrogen embrittlement.

We (company) decline to galvanized chain known to be G70, but often do G30 regalvanizing.
My own lasts about 6-8 years before galvanizing, but then I'm not quibbling about galvanizing prices - I know a place!!
 
Another issue with G70 is that it is very difficult (impossible?) to get shackles that fit and with a matched strength. The common answer is to have larger links, if buying 8mm G70 you would have a couple of 10mm links added at each end (Maggi will do this) which allows you to use 12mm shackles (and the 12mm shackles will better fit the shackle hole in your anchor). If the larger links are at both ends you can then end for end it. If you have a couple of links its the first link that loses its gal and corrodes and you can chop it off.

But maybe you can get high tensile shackles to match in the UK?

Campbell in America have successfully galvanised a G80 chain - though I'm not sure what 'successfully' means. And Manson and Anchor Right both galvanise a 800 MPa steel in their Supreme, Boss and Excels and the Knox anchor is made from a 900 MPa steel and galvanised. For some reason the gal on high tensile steels seems thinner (than on mild steels). There is much talk and fear of Hydrogen Embrittlement in G70 chain but I can find no reference to it having actually occurred, I'd love to see a link! (though as Geoff says - galvanisers will not regalvanise and both Maggi and Peerless conduct their own galvanising).

Jonathan
 
I wonder if OP should not hold off on any decisions because if he anchors a lot surely it won't be long before he wants an electric winch. Far better to start the process of buying chain if you have a winch to match it up to. I know very little about this subject but would think 8mm fine and is the rusting really a concern? Either put up with rust or regalvanise what you have. good luck olewill
 
William_H said:
I wonder if OP should not hold off on any decisions because if he anchors a lot surely it won't be long before he wants an electric winch. Far better to start the process of buying chain if you have a winch to match it up to. I know very little about this subject but would think 8mm fine and is the rusting really a concern? Either put up with rust or regalvanise what you have. good luck olewill
Click to expand...

Spot on. Regularly anchoring a 13 ton boat with a manual windless will end in tears - or the back clinic. Get the electric windlass and calibrated chain to match. And get early to get max benefit
 
Just to clarify about hydrogen embrittlement and galvanizing:
Its not the galvanizing that causes problems, its the cleaning beforehand.
Galvanizing is an alloying process, when chemically clean steel is immersed in molten zinc an alloy forms on the surface.

The most common cleaning includes soaking in hydrocloric acid - about 10% strength. Its this acid immersion that can cause H2 embrittlement in high strength steels.
It is possible on a small scale to clean the steel by other means, including mechanically (eg blasting).
Most galvanizers are processing several tonnes of steel an hour, so are not equipped to "muck about" doing fiddly things - they don't pay.
But if a quantity of anything is required, then things become economic.
So an anchor manufacturer might do high strength steel anchors in bulk for example.
 
oldvarnish said:
That set me thinking: Does it matter if my anchor chain is starting to rust? And how rusty can I allow it to get before it makes a difference to its strength?
Click to expand...

The guideline usually quoted as the limit is 10% loss of cross-sectional area. This usually occurs at the points where adjacent links cross, due to a combination of corrosion and wear. Other than the marks made by the rust on the boat, rusting itself is not harmful.
 
As Viv says for an anchor chain that is not actually anchoring for much of its life. Rust is likely to be over much of the link but perhaps starting at the interface between links.
Chain used for a mooring where it is loaded much of the time the rust occurs in the interface betwen links but becuase this rust is imediately worn off by the load new rust forms so that in a surprisingly short time a chain will have very thin link at the point wehere the links touch. of course it fails then.
For an anchor chain where actual load time is not much then rust should not be a great concern for strength. Do check the rubbing points between links however. On my mooring chain (much heavier because of this problem) I reckoned at about 50% thickness loss I would replace. 10% might be right for an anchor chain. olewill
 
Mooring chain does not rust, or not much (its under water and has little access to oxygen and the gal, if there was any in the first place, gets worn of quickly). Mooring chain is worn away by simple abrasion (sand between the crowns of the links and rubbing on the sea bed - but the rubbing of one link against the other is the killer).

The same occurs on an anchor chain, but once the gal has gone (where the 2 links rub) there will then be corrosion (because once it is lifted it sits in the anchor locker, lots of oxygen and salt. But anchor chain, toward the anchor end, is subject to being swept across the seabed and I notice that rusting anchor chain can have huge flakes of rust along the 'long' of the link. Where the weakest point is - I'm not sure (but the load will be on the crown). So there are 2 points of wear in an anchor chain, at the crowns - through abrasion, and on the outside of the links where they rub the seabed (one is metal to metal with sand the other just sand) loose gal and then both areas corrode.

Its at this point (in the absence of any tests) that the idea of a chain that has been properly galvansed (or galvanising that last longest) becomes important (as the galvanising of the whole link is important) - and in the absence of any other information I'd go for a supplier with a reputation (to protect).

But Vyv makes the comment that a 10% loss of link size is a measure of when to retire chain - I suspect this will occur by corrosion before wear (we use our chains insufficient to wear that 10%) so corrosion is the rate control - so go for the best galvanising.

Maybe we need a thread on how quickly specific suppliers chain needs re-galvanising - as subjective topic to rival anchor threads:)

There will be some results on the abrasion resistance of galvanising of, or from, different suppliers - but maybe these tests have already been done?


Geoff, MMSAHO - any references to HE, from whatever cause, (I acknowledge that acid is oft quoted) causing failure of G7 chain.

Jonathan
 
This is a mooring chain, abraded by dragging on a sandy seabed.
IMG_2151.jpg
 
Interesting stuff. Ta for all the replies. Vyv that picture is amazing! Thinking now that grade 40 from bradney is probably the way forward.

Electric winch... not for me. Would hate to rely on it only to have it fail at an inappropriate moment. .. by which point my biceps would have atrophied and we'd be in a proper pickle!

First hoist or two of the season is hard work but by the end I rarely use the manual winch at all and I'm strong as an ox! :) I argue the same about outboards and rowing.
 
>But we anchor rather a lot, for extended periods of time, so I'm concerned about crevice corrosion in stainless chain... and the price makes me weak at the knees anyway.

That happened in Trinidad and the chain broke, I think it's caused by sand/broken coral scratching the chain as it drags across the bottom. We had almost exactly the same size and weight boat (38 feet and 14 tons fully loaded) and we used 8mm Test chain.
 
Neeves...
I don't have any knowledge of anchor chain suffering embrittlement, but I do of other things made from Hi carbon steel.
But anchor chain is such a minority of steel that is galvanized... There's about 800,000 tonnes a year of steel galvanized in the UK. Nt a high percentage of that is chain.

Galvanized steel submerged in sea water corrodes at very different rates in different place. The worst (fastest) rate is in the Persian Gulf, Arabian Sea area.
Galvanizing normally protects best after it has formed a layer of oxide products on its surface. Shiney galv corrodes quickly.
 
You must log in or register to reply here.

Share this page

Top