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Old 09-10-2019, 13:06   #16
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G70 chain vs G4

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Originally Posted by thinwater View Post
The windlass manufacture worries me. They should know better. More likely, they just don't make the correct gypsy. Another concern is that the structure of the windlass was based on G30 chain and is just not up to the load. G70 is relatively new in the marine market, and you won't find a windlass that was designed from the ground up for it. I can see why they would shy away. (Yes, I understand that the windlass "should" only be lifting the chain and anchor, but we all know, and the manufacture knows, that it will be used to pull the boat to the anchor and break it loose.)



In fact, the yanks a chain gets at anchor are not nearly as sudden as the jolts and vibrations chains face in both hauling and industry. And I'm pretty sure they have thousands of times more experience than sailors.



In fact, G4 chain is not rated for lifting or securing loads because it is NOT as tough (yield before break) or fatigue resistant as G7 chain. It has a history of failure in industry. You can Google this. OSHA and DOT agree. Every industry group agrees.


There is also a misconception that G7 is akin to hardened steel. In fact, it is good grade of spring steel, which is what you use for cyclical loads, like the springs under your car (G4 springs would last long).



This is just a durable urban legend.


I don’t believe so, I believe that grade 40/43 and grade 70 are both mild steel, most likely 4130 or maybe 4340 steel.
The difference is heat treat level, and always, always, always when you gain strength in steel by heat treat, it’s becomes less malleable and more brittle.

However chain meant for overhead lifting is neither 40 or 70 is, is a different much more malleable steel. Both 40 and 70 are subject to failure without much stretch, where chain meant for overhead lifting must stretch quite a bit before failure, giving the operator warning before failure.
Malleability is different from elasticity of course, if you want elasticity, which is not what is required for overhead lifting chain, then that is when your use of “spring” steel comes in.
However please understand that “spring” steel is as descriptive as “plastic” many, many Springs are just tempered mild steel.
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Old 09-10-2019, 17:25   #17
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Re: G70 chain vs G4

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Absolutely false. Weight in the chain is meaningless when it’s pulled straight.
Duh, Catenary is paramount if you pull your chain straight you have not enough scope out and not enough weight in the chain, The better the holding power of the anchor is not to lift the shank. I know if it is blowing 100 knots bla.......
Cheers.
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Old 09-10-2019, 17:28   #18
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Re: G70 chain vs G4

I can tell you that in 40 kts or so with a 10 or 12 to 1 scope out, my chain is tight. I didn’t dive it of course, but you can tell what straight out and tight is.
So certainly in severe winds, say over 80 kts you know it’s going to be very tight.
There is no catenary in high winds on boats and chain used on small boats, perhaps there is on ships. I wouldn’t know.
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Old 09-10-2019, 17:45   #19
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Re: G70 chain vs G4

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I can tell you that in 40 kts or so with a 10 or 12 to 1 scope out, my chain is tight. I didn’t dive it of course, but you can tell what straight out and tight is.
So certainly in severe winds, say over 80 kts you know it’s going to be very tight.
There is no catenary in high winds on boats and chain used on small boats, perhaps there is on ships. I wouldn’t know.
Yes there can be.
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Old 09-10-2019, 18:34   #20
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Re: G70 chain vs G4

To the OP's question.

I run 5/16" Acco G70 on an Ideal windless with a 3/8" BBB gypsy. The differences in link pitch are small enough such that the G70 runs fine.

On the other hand the 5/16" HT (G40) will not run without hangs and skips. This shows up in the difference in pitch.

I have not looked at the differences between 3/8" BBB and 3/8" G43 so I cannot offer any opinions on if it would work.

I should also note that G43 and G70 are (typically?) made from the same alloy wire with the G70 heat treated for greater strength. If one were to heat G70 to a degree that it lost its heat treated strength gains then I would expect it to become much like G43. Never tested by me so....
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Old 10-10-2019, 02:11   #21
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Re: G70 chain vs G4

From the NACM specifications:
“...
Grade 70 Transport Chain: A high quality, high strength carbon steel chain used for load securement. Not to be used in overhead lifting.
Grade 43 High Test Chain: A carbon steel chain widely used in industry, construction, agricultural and lumbering operations. Not to be used in overhead lifting.
Grade 30 Proof Coil Chain: General purpose, carbon steel chain. Used in a wide range of applications. Not to be used in overhead lifting.
...”
https://ia800503.us.archive.org/3/it...chain.2003.pdf
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Old 10-10-2019, 02:16   #22
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Re: G70 chain vs G4

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Originally Posted by peter57 View Post
The less weight result will be less holding power, all good though if you are a marina jockey and don't anchor often.

Experts like Steve Dashew and Peter Smith recommend putting the weight into the anchor, not the chain. Weight of the chain doesn't do nearly as much good for holding power as weight in the anchor.
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Old 10-10-2019, 02:20   #23
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Re: G70 chain vs G4

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Originally Posted by peter57 View Post
Duh, Catenary is paramount if you pull your chain straight you have not enough scope out and not enough weight in the chain, The better the holding power of the anchor is not to lift the shank. I know if it is blowing 100 knots bla.......
Cheers.

There is no amount of scope and no weight of chain which will keep catenary in all conditions. I was somewhat skeptical about this myself, but we did the math and we saw that the experts were right -- catenary goes away in strong conditions.



The really involved discussion with serious engineering analysis of the question:


Possibly Original Thought About Chain Catenary - or - The Myth of the Bar Tight Chain
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Old 10-10-2019, 15:39   #24
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Re: G70 chain vs G4

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Originally Posted by evm1024 View Post
I should also note that G43 and G70 are (typically?) made from the same alloy wire with the G70 heat treated for greater strength. If one were to heat G70 to a degree that it lost its heat treated strength gains then I would expect it to become much like G43. Never tested by me so....
I'm going to walk back this statement as the I cannot find my reference materials to verify it and my memory is....sometimes lacking.

I will say that I had read this on one chain manufactures spec sheet where they used the same steel chemistry for G43 and G70 with the G70 heat treated. But that is my recollection.
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Old 10-10-2019, 19:31   #25
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Re: G70 chain vs G4

I really respect that!
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Old 10-10-2019, 20:01   #26
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Re: G70 chain vs G4

I can find that even some G80 chain is 4130, but oddly I’ve not found that 43 and 70 are.
It may well be that some is and some isn’t, depending on manufacturer, I found that is the case for 80 anyway.

Maybe the “good” stuff isn’t 4130, it may be 4340 or maybe even 5160 or other alloy?
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Old 10-10-2019, 20:06   #27
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Re: G70 chain vs G4

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Originally Posted by Sailmonkey View Post
Absolutely false. Weight in the chain is meaningless when it’s pulled straight.
However, it takes much more wind to "pull straight" a heavy chain with a lot of scope than a lighter chain.

Even in waves the chain does not get "straight", it always has some catenary.

In my experience, we've NEVER come even close to pulling our chain straight, there is always catenary.
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Old 10-10-2019, 21:02   #28
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Re: G70 chain vs G4

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Originally Posted by wingssail View Post
However, it takes much more wind to "pull straight" a heavy chain with a lot of scope than a lighter chain.

Even in waves the chain does not get "straight", it always has some catenary.

In my experience, we've NEVER come even close to pulling our chain straight, there is always catenary.

You can calculate how much force is needed to lift the last link from the seabed with Alain Fraysse's calculators:



Rode - Static Behavior


It is true that there is always some catenary, but even with 12mm chain, the catenary is reduced to millimeters and the chain is behaving like a bar ("bar tight") at forces which realistically exist in real life anchoring situations. The catenary no longer influences the angle of pull on the anchor when the last link is lifted from the seabed.


From the previously quoted catenary thread:



Quote:
Originally Posted by Kelkara View Post
. . . This graph shows the same 100m of 3.3Kg/m chain in 30m of water (3.3:1 scope) with a horizontal pull of 500, 1000, 2000, 4000 and 8000 Kg horizontal force (there will also be 330Kg vertical force). The chain will take the shape of the curve between the dots. 510Kg is the point at which the last link lifts off the bottom and starts to pull up on the anchor, at which point there is only 1.5m of "slack" left in the catenary for snubbing.

Also because I was interested. for the same 100m of chain I plotted the angle of pull at the anchor after the last link starts to lift for 3:1, 4:1, 5:1 and 7:1 scope.

I also plotted how straight the chain is in the same situation ... This seems to be predominately controlled by the force, and not the scope ... these graphs are only for once the anchor starts lifting, and there is essentially no "snub" left in the catenary.


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Old 10-10-2019, 21:35   #29
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Re: G70 chain vs G4

Quite simply when someone states that there will always be some catenary in a chain I have to agree with them. Barring an infinite slope chain.

But, BUT often they fail to take into account the forces that head to an asymptotic infinity as the effective curvature of the catenary approaches zero.

What this means is that at first it takes a few pounds or kg to move the end points of the chain further apart.

Then as the chain comes "tight" the forces are measured in thousands of pounds or kg.

Lastly when the chain is "bar" tight it will take hundresd of thousand pounds or kg of force to flatten the chain further and thus extending the distance between the chain end point another 1 mm.

Can you say brick wall?

Of course something broke long before this point. The catenary of the chain has as much give as hitting water from a 200 meter fall. Zilch! Or should I say splat!

Regardless of the degree of catenary in the bar tight chain there is no effective ability to absorb any further forces - that is reality.
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Old 10-10-2019, 21:41   #30
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Re: G70 chain vs G4

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I really respect that!
Thanks !

- I do recall that when I was researching chain that some chain maker used AISI type 1008 for their G30 (BBB) chains. They used AISI type 1022 steel for their G43. For their G70 they used type 1022 that was quenched and tempered.

But as noted, I am unable to locate the documentation to back this up. I do recall that getting the steel types took a bit of work. And of course G30,G43 etc are specifications of tensile strength rather than a specific steel spec.
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