Bigger is better, part 2

[JonJo]

Noelex,

I cannot but agree.

I only use the absence of evidence of chain failure, and historically it was G3, as some basis on which to 'hang' any 'engineering' data.

Anchors have got better, skills have improved, use of ancillary devices (like snubbers) has increased but people are broadening their horizons and exposing themselves to geography where weather forecasts are less certain - and presumably they get caught out (in winds and waves in an anchorage that they did not quite anticipate - I know we have).

But these is no evidence that G3 chain is basically unsafe, there is no evidence of failure - though accepting that everyone who uses it has a dragging anchor, so does not shock load it, and has always carried chain larger than recommended.

So on the basis it is safe it provides a basis for comparison to G7. Once that comparison is made - and the strengths and weaknesses exposed it might be possible to then say - but because of X, Y and Z we should be looking at G3 + 30% - or something.

I fully agree with your post - I'm simply looking to have explained, quantitatively, the inherent weakness or strength of G7 compared with G3 based on chain of similar UTS.

Jonathan

Edit, I had to check back to one of Andrew's posts

He listed as disadvantageous of G7 (or high tensile chain): potential of stress corrosion cracking, notch sensitivity, lack of toughness, intolerance of unfair damage. I omit the other negative characteristic: re-gal embrittlement as totally valid and mentioned by everyone who mentions G7 chain. You, Noelex have been using your chain for some years now and have enjoyed and described winds of 50 knots as not unusual, you have good anchor (one that sets solid and which could 'generate' shock loads - yet you are not phased by Andrew's comments?

[noelex 77]

Originally Posted by JonJo

You, Noelex have been using your chain for some years now and have enjoyed and described winds of 50 knots as not unusual, you have good anchor (one that sets solid and which could 'generate' shock loads - yet you are not phased by Andrew's comments?

I am not phased by many things

One of the interesting things about anchors, and anchoring systems is that we are at a stage where ideas are changing rapidly.
I anchor most days of the year so need the best gear. The cost is not a great factor considering how much I depend on and use the equipment. I am not wedded to any one way of doing things and if G7 is not the right way go I would change.

We do need to put the risk into perspective. The risk of dragging and damaging the boat (even with the best gear) is by far the greatest risk. Even if you anchor often you are very unlikely to experince a bent anchor shank (or tip ), or broken chain, but you are likely to drag, probably multiple times.

All the chain alternatives do have drawbacks (given the practical limitations of weight). Going thicker means carrying less all chain rode so there will be times when the scope is compromised (increasing the risk of dragging), or rope (with potential chafe problems) is needed. We need to weigh these different risks to come up with a system that is safest. (Andrew idea of using the chain as central low down ballast is great, but there are few boats where this is practical. The Boreal and new Garcia Exploration 45 are the only examples I know of)

Andrew is a great practical engineer and I am very interested in what he has to say. I think with more discussion I will be able to determine the suitability (or perhaps quantify the risk) of using 10mm G7 on my boat. This is what is great about these discussions on CF. I am always happy to hear suggestions that would make my anchoring safer.

[Andrew Troup]

JonJo, Noelex


As a "practical" engineer (thanks Noelex!) I am very sensitive (over-sensitive, by the standards of most) to the risks attached to a "winners uber alles" mentality.

Here's what I mean by that. However the ex-works elongation figures are arrived at for a given high-tensile steel, I can assure you they are NOT arrived at by doing the following:

(moving from the highly controlled lab environment to the factory environment for the first few steps, and the nasty, uncontrolled real world for the remainder):

- bending the sample through a couple of 180 degree bends
- butt welding the sample at the midpoint (probably without filler rod)
- galvanising the sample
- subjecting the sample to hundreds of thousands of (sub-failure) strain-aging stress cycles prior to test
- chipping / wearing off the galv on the insides of the bends (the point of greatest contact stress)
- immersing the sample in a mildly corrosive environment (some muds are worse than 'mildly' corrosive, come to think of it)
- watercooling the sample to single digit temperatures
- loading it at its LEAST favourite rate, off-axis

and having perpetrated all those insults to the sample, the unkindest cut of all:
- choosing the worst-performing of one thousand samples

Because bitter experience teaches that (particularly for 'high performance' alloys) failure is seldom attributable to a single cause or even a couple of causes: it's generally closer to "death by a thousand tiny cuts".

Simple materials like mild steel fail in simple ways. Complicated materials fail in complicated ways.

As a practical engineer, I am emphatically NOT interested in the best performance a material can summon in the lab; I need to pay heed to the WORST performance it might achieve in the real world.

It's a close relative, I guess, to my concerns about anchors increasingly being "taught to the test" (ie designed to shine under anchor test conditions)

Having said all that, I want to reassure people with G70 chain that I think my arguments in this thread reflect my sensitivities and peculiarities, more than those of that particular material.

There is a sweet spot, at about that strength level, where the toughness properties of carefully concocted alloy steels *can* be (almost) 'too good to be true'.

And the experiences of people like Nick on Jedi (and other early adopters) suggest that old-school chains, sized for catenary effect and made from alloys not much above mild steel, were SO understressed that it's possible to get away with the sort of radical resizing which Steve Dashew trailblazed.

- - - - -

So from here on I will restrict myself to arguing against the future use, for anchor chain, of even higher-tensile steels, intended for lifting. (As tentatively put up for discussion by JonJo)

Here I'm more confident that I am not going to run the risk of unfairly over-egging the argument. I am confident that G80 is a bridge too far.

[JonJo]

Andrew,

If I can interject, right at the start.

Current, or historic, galvanising of G70 chain detracts from the strength of the original chain as a result of the heat of the galvanising process. Basically the heat of galvanising is so near the tempering process than Gal G70 chain has a lower, by about 15%, UTS compared to the ungal G70. I do not know how other characteristics of G70 chain are impacted, like YS, deformation. But there are developments in HDG which mitigate these problems.

But there are also other, economic, ways to provide a galvanising finish that can produce a corrosion resistant zinc coating and these have been used on G80 chain (and actually a G100 chain) with only a 10% loss in UTS, again I do not know how these processes might impact YS - and elasticity or anything else. It is thought that possibly it will be practical to zinc coat a G80 (maybe G100 - one step at a time) without any loss of UTS and do so economically. There is some commercial pressure, other than the tiny anchor market, so developments will occur.

Maybe thus the debate can ignore the galvanising issue as events might overtake us. But any comments need to be viewed with the proviso that any heat treatment, however good, might impact comments positively or negatively. Also it merits comment that Gal G7 has been around for some time but there is virtually no technical information on the product, except that in the West Marine catalogue, which defines UTS and WLL (and I think these are questionable) but there is no information on even the simplest perameters: elasticity, yield, deformation etc

Now back to the experts

Jonathan

[nigel1]

This has been an interesting thread, but not one I should have been reading while spending 18 hrs anchored with sustained wind speed of 30 kts, of which 6 hours of 40kts and gusting to +50. But, it did help keep me awake.

[Alan Mighty]

Originally Posted by nigel1

This has been an interesting thread, but not one I should have been reading while spending 18 hrs anchored with sustained wind speed of 30 kts, of which 6 hours of 40kts and gusting to +50. But, it did help keep me awake.

How deeply embedded was your anchor when power set before wind and how more deeply embedded was anchor after wind?

Al

[Dockhead]

Originally Posted by nigel1

This has been an interesting thread, but not one I should have been reading while spending 18 hrs anchored with sustained wind speed of 30 kts, of which 6 hours of 40kts and gusting to +50. But, it did help keep me awake.

Oh, come on Nigel. Par for the course in the British Isles. Why, you work in the North Sea!

[nigel1]

Originally Posted by Alan Mighty

How deeply embedded was your anchor when power set before wind and how more deeply embedded was anchor after wind?

Al

No idea how deep it set when deployed, (water way to cold, and single handed, to dive on the anchor)
Took 20 minutes to break out, so it was well dug in.

[nigel1]

Originally Posted by Dockhead

Oh, come on Nigel. Par for the course in the British Isles. Why, you work in the North Sea!

When I came into Cemaes Bay, at first attempt to anchor, it dragged.
Not a good situation, Force 7 winds and single handed. Was a real struggle to get the anchor back up, and when I did, it was to find an old lobster pot hanging from it.
I spent the next half hour going from cockpit to bow, checking boats position and attempting to clear the anchor, no easy task on your own.
By the time it was clear, I'd drifted about a mile out to sea, and then had to claw my way back into to the bay.
Think that experience really rattled me. The second attempt at anchoring went fine, but left me pretty much unnerved for the duration, and also pondering on lots of "what if's".

[Pelagic]

Is there a relationship between tensile strength and how well a metal can be galvanized?

[Dockhead]

Originally Posted by nigel1

When I came into Cemaes Bay, at first attempt to anchor, it dragged.
Not a good situation, Force 7 winds and single handed. Was a real struggle to get the anchor back up, and when I did, it was to find an old lobster pot hanging from it.
I spent the next half hour going from cockpit to bow, checking boats position and attempting to clear the anchor, no easy task on your own.
By the time it was clear, I'd drifted about a mile out to sea, and then had to claw my way back into to the bay.
Think that experience really rattled me. The second attempt at anchoring went fine, but left me pretty much unnerved for the duration, and also pondering on lots of "what if's".

I can imagine. Anchoring in a F7 single-handed would not be a picnic anywhere, and even without a fouled anchor.

I've fouled my anchor on all kinds of carp, including old pot moorings, and even an old chair one time (!).

[Marqus]

Originally Posted by Andrew Troup

- bending the sample through a couple of 180 degree bends
- butt welding the sample at the midpoint (probably without filler rod)
- galvanising the sample
- subjecting the sample to hundreds of thousands of (sub-failure) strain-aging stress cycles prior to test
- chipping / wearing off the galv on the insides of the bends (the point of greatest contact stress)
- immersing the sample in a mildly corrosive environment (some muds are worse than 'mildly' corrosive, come to think of it)
- watercooling the sample to single digit temperatures
- loading it at its LEAST favourite rate, off-axis

and having perpetrated all those insults to the sample, the unkindest cut of all:
- choosing the worst-performing of one thousand samples

May I ask, Andrew, what the reason is that the above factors impact more severely on higher tensile chain such as G7, than on G4 and G3 (if you are indeed saying it is the case)?

[JonJo]

Originally Posted by Marqus

May I ask, Andrew, what the reason is that the above factors impact more severely on higher tensile chain such as G7, than on G4 and G3 (if you are indeed saying it is the case)?

I find it difficult to imagine many steels that can be bent through 180 degrees. I'm also not sure how many of us, in reality, subject our chains to low temperatures (though it does raise the issue of storing ones yacht on the hard through the winter with the chain neatly laid out under the hull).

Jonathan

[Andrew Troup]

Originally Posted by Marqus

May I ask, Andrew, what the reason is that the above factors impact more severely on higher tensile chain such as G7, than on G4 and G3 (if you are indeed saying it is the case)?

If there is a single reason, it's something like "the gods must hate us", or more specifically, become jealous when we aspire to godliness.

I'm only partly joking. If you're asking for a technical reason, the best I can do is what I've already said: "simple materials (like mild steel) fail in simple ways; complicated materials fail in complicated ways"

Materials I would class as complicated include very high tensile steels, whose metallurgy is based on a number of very finely judged, high-wire balancing acts.

It has taken most of my lifetime to work the bugs out of another complicated material: carbon fibre, to the point where it is reliable enough for mainstream use.

Each of the considerations I mentioned have multiple reasons why they present more of a challenge to very high tensile steels, and in order to make those reasons comprehensible to those who didn't read the list and nod their heads sagely at each point, I would have to give up my day job and write a not-so-short course.

JonJo: (so you won't thing I'm taking a serious dig, just taking the piss)

Did you imagine that chain links were carved from solid billet, or cast, or 3D printed? I'm struggling to think of how else they could be made without bending the straight "wire" (ie rod) through 180 degrees, in two places, for every link.

There are some fantastic videos on youTube of chain-making machines in action, BTW.

[JonJo]

[QUOTE=Andrew Troup;1513285]

JonJo: (so you won't thing I'm taking a serious dig, just taking the piss)

Did you imagine that chain links were carved from solid billet, or cast, or 3D printed? I'm struggling to think of how else they could be made without bending the straight "wire" (ie rod) through 180 degrees, in two places, for every link.

There are some fantastic videos on youTube of chain-making machines in action, BTW.[/QUOTE

Sorry, I thought you were talking about our using it!

I've seen the videos, repetitous but strangely compulsive viewing (and in real life awfully noisy).

I've never seen a Q&T chain video, or its not been portrayed as such - I had fondly and naively thought the Q&T process was downstream after bending and welding - another illusion destroyed

Jonathan