What Size Anchor Chain ? (Again!)

[GMac]

Using the 2 most common 10mm-3/8" chains. You could say the EU's 3/8" and the USA's 10mm.

A Grade 40 metric 10mm chain.
WLL 1600kg (3500lb)
A G40 will break at 6400kg (14200lbs)
Design/Safety margin is 4:1

A Grade 43 US 3/8" chain.
WLL 5400lbs (2450kg)
A G43 will break at 15200lbs (6900kg)
Design/Safety margin is smaller than 3:1

So if we exclude the tiny difference for physical size and the G40 V the G43 bits, both of which work in the 3/8" favour, we see both the chains basically bust at the same time. Yet quite different WLL's and as we can see it's all due to the Safety Margins used. Hence the term 'Hi Test'.

So while both are damn good chains in a good grade for a boats anchor system and the users of the US G40 have good amount of reserve between their WLL's and BL's, the Italian yacht anchored off his beam has a lot more.

NOTE: This design/safety margin is pretty much peculiar to US G40/43 only. Apart from the Maggi AQUA Tuff Chain G4 and G7 range, which has a 5:1 safety margin there aren't many others out there in anchoring application land anyone will run into commonly. All other anchoring chains run a 4:1 margin, including the US BBB.

[carstenb]

Well I have to say this is one of the most interesting threads I have seen here. I'm enough of an engineer to buy into the less weight in the chain, more in the anchor theory. But regarding snubbers:

Nylon snubbers - sure lots of stretch. Why not increase the stretch factor by putting rubber "Dogbone" or two on the nylon?

[colemj]

Originally Posted by GMac

I think you will find the trouble Acco had with the rusty chain was with their 'premium imported' chain not the one they make.

Good to see you back posting Gmac. If we had the "premium imported" version of the Acco chain, that would greatly surprise their distributer (Defender Industries) that we bought it from. Defender worked hard with me to get Acco to take ownership of the problem, but Acco went AWOL on us instead.

And 12 other boats from the US who bought Acco chain from West Marine and other chandleries would have to have been similarly duped also.

Mark

[Jim Cate]

For G-Mac:

There has been some talk in this thread that G-40 (and above) rust much more readily than G-30. I have my doubts, and wonder if you can shed any factual light on the subject?

My guess is differences in the galvo, not the rust-susceptibility of the alloys involved, but I have no data to base that upon.

Cheers,

Jim

[bruce smith]

I brought it up , and I have no data , only my experience. But as I mentioned, hardened steel rusts more readily than mild steel . I wonder if the molecules of zinc do not get "in there" as well ?

[DumnMad]

Galvanizing thickness can be controlled by the manufacturer. Depends on temperatures differences and immersion time. Need to ask the suppliers what coating thickness is being supplied. There are various standards for various products. As you can imagine some chain could be cheap and nasty.

[GMac]

G'day colemj, nice to be back and I have been popping in but been busy as. We swapped some chain on a couple of boats in the Caribbean. They had 'premium imported' ex Acco and LOTS of rust in no time flat. I have a listing which has 'stuff on it ' Can you PM me any stamping the chains had?

Jim, in a word G40 will rust more than G30 is, hunting for the technical phrase here, Oh yes that's it, 'total rubbish'. The rust issues many chains have today is very simple, crap metal. There are some localised shortish term issues generated by the changing processes used by galvanisers in response to Govts doing Global Warming stuff but that generally means the galvanising looks bloody horrible as there is masses of it. Interestingly people seem to hate that and say it looks yucky. Galvanising is a sacrificial layer and you're complaining there is too much??? Errr.... OK, another one for the weird files.

Below is a photo off a boat who has a anal owner who keeps very sharp records of everything so the below can be pinned down to exactly what it is and when it was fitted. The chain on the left is a Maggi made (Italy) that has been on the boat 7 years. It's a Grade 40 as Maggi don't make lower grades. In the middle is a Crosby (Canada) CLink. On the right is a nearly 2 year old chain that is marketed as being engineered in a North American country. It is just entering the 'flackey rust' stage and far from uncommon to be seen here with chinese made chains, as that one sure is. That one is a Titan brand I'd say, knowing where the dude brought it and what they sell. It sure isn't the other brand they sell, PWB out of Aussie.

So if anyone suggests a G40 is more prone to rust than a G30, what they really mean to say is 'the grade has very little to do with it, that rusty crap was probably made in the east'. Simple steel quality or lack of. We've seen it so many times over so long it's well known what and why now.

We have been monitoring some of the Maggi AQUA7 stuff, a grade 70, and that's showing no more signs of rust than any other reputably made chain. That is a hi tensile chain so it real hard. It is unusual to see hi tensile chains go flacking rust like the mild steels do.

carstenb. Being an engineer you'd be able to do a few quick real life checks yourself just to check the theory wouldn't you? A lot of that thinking is just a US thing where they do tend to use smaller sizes and lengths than many other countries. 99% of US imports here have their anchoring gear dumped and replaced as the 1st thing that happens. The gear is OK but it just wouldn't work in our conditions as it's too small and too short. 45 plus footers with 20 ft of 1/4" chain, hello, what windless waveless planet does that one boat on. Here that 45fter would have 100ft of 3/8" minimum, most would have a lot more and yet many will still be seen drifting around bays, mind you almost all of that is due to the most dangerous thing known to a anchoring system, the boats operator

Anchor chain is a very simple subject as chain is one of the oldest man made products. What you are seeing with most of the wa-wa, engineered in, made for, blaa blaa along with no to very little load or other information attached to the product is only marketing so they don't have to say 'made in china' and 'we hope the loads are XXX' or worse but still seen way to often 'It's good stuff and we're pretty sure we welded all the links'. Yes unwelded links are still popping up with spooky frequency.

The dogbones don't add much in the way of length. Sure they are better than not having them but the same amount of $$ spent on extra rope length would give more benefits.

Anyway that's the ponderings or wonderings for this dude for the arvo. Take care all.

[Jim Cate]

Originally Posted by GMac

Jim, in a word G40 will rust more than G30 is, hunting for the technical phrase here, Oh yes that's it, 'total rubbish'. The rust issues many chains have today is very simple, crap metal. There are some localised shortish term issues generated by the changing processes used by galvanisers in response to Govts doing Global Warming stuff but that generally means the galvanising looks bloody horrible as there is masses of it. Interestingly people seem to hate that and say it looks yucky. Galvanising is a sacrificial layer and you're complaining there is too much??? Errr.... OK, another one for the weird files.


So if anyone suggests a G40 is more prone to rust than a G30, what they really mean to say is 'the grade has very little to do with it, that rusty crap was probably made in the east'. Simple steel quality or lack of. We've seen it so many times over so long it's well known what and why now.

We have been monitoring some of the Maggi AQUA7 stuff, a grade 70, and that's showing no more signs of rust than any other reputably made chain. That is a hi tensile chain so it real hard. It is unusual to see hi tensile chains go flacking rust like the mild steels do.



Anyway that's the ponderings or wonderings for this dude for the arvo. Take care all.

G'Day G-Mac, and thanks for the response. But I surely was not complaining about too thick a galvo layer, so please remove me from your weirdo files. All I was after was conformation that G-40 was not more rust prone than lesser grades, and you have supplied that info.

Being the cheap bastard that I am, our 10 mm chain has been re-galvanized a few times with varying degrees of success. The last effort, done in Bundaberg Qld did indeed have masses of zinc. I didn't care about the "yucky" appearance, but I did hate that the thicker layer caused the chain to hang up in the pockets in the gypsy and jam in the chain pipe. That is a real PITA!

Anyway, thanks for clarifying the rust issue, especially seeing that what you said agreed with my instincts.

Cheers,

Jim

[GMac]

No panic Jim, you hadn't been classified as a weirdo, that bit was just a side ramble.

Queensland is a state that is moving to squish emissions and in doing that is causing the galvanisers some grief trying to comply. That is why you have that chunky galvanising. Part of the process that makes it look 'pretty' is apparently releases an environmental nasty so while it's still well galved it can look yucky. But then use it 2 or 3 times and most would never know.

No worries at all re-galvanising but be aware if the person doing it is a bunny they can lose it a lot of strength. More to watch for in the higher grades than the lower. Also some galvanisers are now unwilling to reglav chinese made as the soft steels they use means the regalv will blow off fast and the punters then bitch to the galvanisers about poor work. So they are increasingly saying 'Nope, sorry'.

[jnrdafoe]

Has anyone had experience with Rigging Products, Inc. of Portland OR, USA?
Suppliers of anchor chain and shackles. Their prices seem reasonable and the chain specs look good.

Jim

[MathiasW]

So, it seems I am again late by 10 years in finding this interesting thread!

Some have argued that this is not a topic one can solve mathematically, whilst others asked for some mathematician to do the maths... See further below...

I do wonder how anyone who is not believing this to be a tractable topic for engineering can sleep well on a long-haul intercontinental flight...

Anyway, I have used the Corona time to work quite a bit on the mathematics and modelling of anchoring. It is not complete, far from it, but I believe it does advance the field a little. And I do hope it provides further insights to the community so that everybody can better form his or her own opinion about this matter.

Many seem to suggest that there is no catenary when you most need it in a severe storm. That is simply a question of how long the chain is. For any storm a sufficiently long chain can be calculated such that catenary still works in that the chain pulls only horizontally at the anchor shank. And, you may be surprised to hear, when anchoring in deep water, like 20 metres or so, the catenary approach actually yields a shorter chain length than, e.g., a 9:1 scope approach. So, do not be misled by just looking at the chain at the bow. Yes, it will be stiff and straight as a ruler, but this does not mean it cannot be a catenary under water, close to the anchor...

In very shallow water, on the other hand, a scope approach often underestimates the required minimum chain length, and then it gets dangerous.

With regards to thin versus thick chains: A thicker chain will reduce your swinging circle and this is greatly appreciated in crowded anchorages. However, for the same total weight of chain in your locker, a thin chain allows you to anchor in deeper water than the heavier chain does. This comes straight out of catenary calculations. So, the choice for our trimaran SAN has been to use a high-grade 10 mm chain (as opposed to the factory default of 12 mm), but have much more of it: 102 m. Plus, a heavier anchor than the ship yard supplies...

Going for a thinner but longer chain can make the difference between yes, I can stay at this anchorage and anchor at the deep side, or I have to move on and find another place. Also, folks in strong tidal waters will appreciate thinner chains over thicker chains for this reason. But again, a thin chain requires a larger swinging circle, and this may prove an issue in crowded places, so a compromise may have to be found, which will vary depending on your typical sailing area.

Finally, the question whether the catenary will help dampening the jerking at the chain. Firstly, yes, do use a good long snubber (and here I mean 10 metres or so), or for a multihull a good long bridle, and yes, do use a rubber dog-bone spring as well. We have 13 m nylon bridles with two rubber dog-bones in each leg.

But the chain can help absorbing shocks by getting lifted higher off the seabed, thereby increasing its potential energy - and this I believe is the new element I can add to this discussion. I have modelled this potential-energy effect. Even in severe storm, if the chain is long enough, it will store some energy. This works well in deep water, but when it gets very shallow, the angle of the chain is so small that there is not much room left for lifting the chain any further. So, in such a situation, only very little kinetic energy of the vessel can be stored as additional potential energy of the chain. This is when snubbers become vital. Without them, the load on the anchor can become so high that one has to relocate to deeper water to help reduce this load.

If you are interested in more analysis - I have created a set of brief digests for vessels of various windage areas and chain thicknesses that contain graphs with minimal chain length as a function of wind, water depth, chain thickness and energy bursts (i.e. swell). They also contain graphs of the anchor load. Have a look here:

https://trimaran-san.de/die-kettenku...atiker-ankert/

The biggest issue in applying it to your vessel is to work out the effective windage area of your vessel, but this can be done with a scale whilst hanging off a post in the water (not in a storm, though ).

Just for the fun of it, I also tried to work it out for huge commercial vessels. Their chains and windage areas are much larger than our recreational vessels (or live-aboard vessels), but it is only the ratio that counts: Windage area divided by chain weight in water. That is the characteristic parameter of the catenary.