Anchor Chain Question

[Matt sachs]

BBB = Bend Before Breaking

[Matt sachs]

Its funny how the birth of a child can put projects on hold....Im back at it now. Today I bought a drum of G4 3/8 acco chain. Next week Ill order the Maxwell RC 12-12 windlass. Cant wait to get family on the water....

[evm1024]

Originally Posted by skipmac

Well not quite as simple as that which is why I spent so much time researching it. For example, one can also get a G70 chain which is even stronger than the G40 However the stronger chains are less forgiving of repeated shock loads and can work harden and get brittle and snap. This can build over time so an older chain that has been through some bad storms and jerks on the rode may have lost a good bit of it's safety margin. In fact I have read recommendations that G70 chain be replaced if it has been highly stressed or the links show any stretching at all.

So BBB from what I understand will stretch more before breaking where the stronger chains tend to fail more suddenly and catastrophically.

My current preference is the G40 chain as the best compromise.

I use 5/16" G70 on a 32,000 pound, 50' boat. I want to address some of the thoughts expressed in the quote above (with no slight to the poster).

When thinking of steel specs we need to keep the Stress/Strain relationship in mind. For any given steel as we apply more force (stress = force per unit area) the length of the steel increases (strain = deformation of a solid due to stress.

Up to the Yield Strength this stretching is elastic and when the force is removed the piece returns to its original length without any damage. Ready and able to do it all again. When stressed above the yield strength the piece will elongate past its elastic limit and deform. This deformation has at least 2 forms. Firstly, the crystal structure changes internally to the steel. secondly, the diameter of the piece will decrease. Crystal structure changes result in work hardening. The steel becomes stronger and harder typically but due to the reduction in diameter eventually the steel necks off and a fracture happens ( see photo).

Shock loads are rapid forces applied to a material. Even though the load happens quickly the force is still very much like a static force of the same value. What is special is that the shock force can be quite a bit higher than the static force. For example you are in a blow and there is 500 pounds wind load on your boat. The surge due to wave action can easily be 2 to 4 times higher giving a peak load of 2000 pounds.

If that shock load exceeds the yield strength of the steel then you will see deformation.

In a steel such as used in G30 chain the yield strength runs about 50% of the ultimate strength. Thus G30 elongates considerably as it is overloaded. It has a 50% margin between yield strength and ultimate strength after all.

In a steel such as used in G70 chain the yield strength runs about 90% of the ultimate strength. Thus G70 elongates very little as it is overloaded and appears to "just snap" with the 10% margin between yield strength and ultimate strength.

So, if you have any deformation of G70 chain (either in length or in diameter) then you have exceeded its yield strength (true for G30 as well of course). Basically you have stressed the chain to within 10 % of its breaking strength (in shock loads or otherwise). Not a good thing. replace it and use a better snubber.

In any case - G30 or G70 - if you have exceeded its yield strength you will have deformation (elongation and reduced diameter). It will likely not run through your windlass well and needs to be replaced. The key is to measure the diameter of the chain when you get it and then again every now and again and if it has reduced its diameter below the NACM specs you should replace it. Much harder to exceed G70s yield strength but more dire if you do.

Lets look at this from another angle. Say that you are using 5/16 G70 with a breaking force of 18,800 pounds. 90% of this is 16,920 and is a good number for the yield strength.

What size G30 chain has a yield strength of 16,920? With the yield strength for G30 about half the UTS we would need a chain of 33,840 breaking strength. This is between 5/8" (27,600) and 3/4" (42,400).

(Mega disclaimers follow) You mileage and number may vary from mine - by a lot. No data included for crystal structure deformations due to sub yield strength repetitive loads which MAY cause G70 to become "brittle" after years of anchoring. etc, etc, Etc. Yes, yes, yes - I know that the photo is aluminum but is has a much greater reduction of diameter before fracturing. It shows the point better. And lastly I may be full of poop so do your own research and draw your own conclusions. Happy sailing.

[Jim Cate]

Evm1024,

Very nice post! Well done...

Jim

[skipmac]

Originally Posted by evm1024

I use 5/16" G70 on a 32,000 pound, 50' boat. I want to address some of the thoughts expressed in the quote above (with no slight to the poster).

When thinking of steel specs we need to keep the Stress/Strain relationship in mind. For any given steel as we apply more force (stress = force per unit area) the length of the steel increases (strain = deformation of a solid due to stress.

Up to the Yield Strength this stretching is elastic and when the force is removed the piece returns to its original length without any damage. Ready and able to do it all again. When stressed above the yield strength the piece will elongate past its elastic limit and deform. This deformation has at least 2 forms. Firstly, the crystal structure changes internally to the steel. secondly, the diameter of the piece will decrease. Crystal structure changes result in work hardening. The steel becomes stronger and harder typically but due to the reduction in diameter eventually the steel necks off and a fracture happens ( see photo).

Shock loads are rapid forces applied to a material. Even though the load happens quickly the force is still very much like a static force of the same value. What is special is that the shock force can be quite a bit higher than the static force. For example you are in a blow and there is 500 pounds wind load on your boat. The surge due to wave action can easily be 2 to 4 times higher giving a peak load of 2000 pounds.

If that shock load exceeds the yield strength of the steel then you will see deformation.

In a steel such as used in G30 chain the yield strength runs about 50% of the ultimate strength. Thus G30 elongates considerably as it is overloaded. It has a 50% margin between yield strength and ultimate strength after all.

In a steel such as used in G70 chain the yield strength runs about 90% of the ultimate strength. Thus G70 elongates very little as it is overloaded and appears to "just snap" with the 10% margin between yield strength and ultimate strength.

So, if you have any deformation of G70 chain (either in length or in diameter) then you have exceeded its yield strength (true for G30 as well of course). Basically you have stressed the chain to within 10 % of its breaking strength (in shock loads or otherwise). Not a good thing. replace it and use a better snubber.

In any case - G30 or G70 - if you have exceeded its yield strength you will have deformation (elongation and reduced diameter). It will likely not run through your windlass well and needs to be replaced. The key is to measure the diameter of the chain when you get it and then again every now and again and if it has reduced its diameter below the NACM specs you should replace it. Much harder to exceed G70s yield strength but more dire if you do.

Lets look at this from another angle. Say that you are using 5/16 G70 with a breaking force of 18,800 pounds. 90% of this is 16,920 and is a good number for the yield strength.

What size G30 chain has a yield strength of 16,920? With the yield strength for G30 about half the UTS we would need a chain of 33,840 breaking strength. This is between 5/8" (27,600) and 3/4" (42,400).

(Mega disclaimers follow) You mileage and number may vary from mine - by a lot. No data included for crystal structure deformations due to sub yield strength repetitive loads which MAY cause G70 to become "brittle" after years of anchoring. etc, etc, Etc. Yes, yes, yes - I know that the photo is aluminum but is has a much greater reduction of diameter before fracturing. It shows the point better. And lastly I may be full of poop so do your own research and draw your own conclusions. Happy sailing.

No slight taken and your addition to the discussion is very welcome. Let me confess that even though I have a background in engineering it is in no way related to materials, metallurgy, etc. The closest I came to that field was a couple of courses in static and dynamic force and load analysis.

So all I posted about various chain grades was based to some degree on some basic research, specs and data but more based on opinions and articles from "experts" (scary thought, eh?). However, like anything else about boats even "experts" don't agree. Even when there is agreement on the data there are different opinions on the interpretation of the data and which tradeoffs or compromises offer the best results.

So, all that being said, I did a good bit of research and have some understanding (IE enough knowledge to be dangerous) of the issues you addressed like shock loading, crystallization, etc. and came away very undecided. Yes G70 is much stronger but how much of an issue is the potential for work hardening? In a previous discussion on CF a few years ago if I recall a knowledgeable member strongly recommended against G70 for that reason. But the additional strength is very significant.

Bottom line, the more I have researched chain alloys the less certain I am of which way to go. I'm 99% certain that I would go G40 or better. And this doesn't even address the issue of the quality of the galvanizing (I've heard some complaints about even top grade US made chain recently). Then you get into link dimensions and the fun really begins. If I recall I found at least 3 or 4 very different link specs for sizes commonly used for anchor chain.

So your opinion on brand? Acco the way to go or has their galvanizing quality gone down? What about the Italian made chain? I've been hearing good things about it.

[zboss]

SkipMac,

Very interesting this topic on Galvanization just came up. Practical Sailor just completed a test on various chain galvanizations and found that regular BBB Peerless beat out the expensive g4 Italian chain when it comes to the quality of the galvanization. They also found that the breaking strength of the peerless BBB is much higher than the specs indicate.

[evm1024]

Experts... There are no experts in recreational boating chain design. There are people who have a lot of experience. And many who have strong opinions far too often without the numbers to back it up. And we all know that.

Take hydrogen embrittlement for example. Some 'experts" are quite worried about it. Yet, the general professional thought is that it is not an issue for lessor that G100 carbon steels.

Chain is (um, well) chain. The minimum spec for 3/8" G43 is spelled out in the NACM welded steel chain specs for example. The maker of the chain can select the steel and treatment (in G70 for example) of the base wire to make chain that meets the spec for the specific chain.

The key here is that the manufacturer must have the quality controls in place to actually make the chain meet the spec.

Acco and Maggi for example have strict quality controls in place to ensure that their chains meet or exceed the full specifications for each grade of chain they produce. They take pride in the quality of their chain.

Other companies make chain knowing full well that their corporate name is not riding on the chain, that it will be rebranded and resold. And quite frankly they work in a corporate environment that does not value excellence but rather looks to shortcuts for profit.

G70 is G43 that has been heat treated. Galvanizing reduces G70 strength about 15%to 20% from ungalvanized G70.

(Boy really digging back in my past) G70 is heat treated beyond the upper transitioning temp (A3) then quenched. The steel at that point is too hard and brittle so it is tempered. The steel is heated to the tempering temperature then air cooled. The exact tempering temp and time to get G70 depends on the actual composition of the steel. In any case it is above the temp of Zinc used to galvanize (820 to 860 F) but well below the A3 temp (1670F).

Of specific interest is that the lower the tempering temp the harder the steel. And thus if the galvanizing temp is below the temp used for tempering we would not see any additional loss in strength. This is why we want to keep any second galvanizing of G70 at "normal" galvanizing temps. If the galvanizing bath is higher than the tempering temp we lose strength.

Who knows what the tempering temp is for any specific manufacturers chain. They might not say....

Work hardening is tough to say. Take lifting chain of G80 or G100 grade. Let's say you are unloading a container ship. Every time the container is accelerated up or decelerated when going down the chain is receiving a shock load (e.g. you do feel increased weight when stopping in a downward elevator). These chains experience thousands and thousands of shock loads often doubling the force. And yet those chains are not retired based on hours of use. OSHA recommends that inspection interval of these chains is set by use and severity of conditions. It is the inspection that will cause a chain to be taken out of service....

Goes back to inspecting your anchor chain.

Regards

PS Quality chain is Quality chain - the rest is details

[Jim Cate]

Again, very interesting stuff EVM, and thanks once more for a good post.

But for all who are following this thread...

In the real cruising world, chain failure is extremely rare. Worrying about the details of metallurgy and ultimate strength is probably not too constructive. The standard practices for matching chain to boat have worked pretty well for a long time. IMO trying to pare down the chain to save a few tens of kgs in the bow is not a great way to marginally improve pitching moment. Having a conservative chain rode made up of something less than G-70 grade product should satisfy for years of worry free anchoring, shocking, galvanizing and wearing.

Jim

[Mark Zarley]

Shock loads to your anchor chain with a snubber or bridal are gentle, compared to the shock loads of a dozer pulling out a stuck overloaded dump truck. I have seen elongation of my 1/2 inBBB chain links due to the links rusting (failure of galvanizing) which results in it being out of time with the gypsy. I need to replace it every 10 yrs (end for end it @ the 1/2 way pt) due to 8 months of anchoring out. My opinion is the chain needs to be large enough to waste away so you can get your moneys worth, without worrying about it breaking and loosing your ground tackle. So the larger, allowing for more loss-age, is the better

[Eleuthera 2014]

Google "cox engineering" then go to chains. All will become clear

:-)

HNY

[Matt sachs]

Its here! woo hoo!, yes Im a nerd. 400 ft of G4. Now...where to cut it? should I put 300 ft on one side and 100 on the other? 200 on each side?

[Matt sachs]

I liked the Ultra Swivel, until I looked at the price. Any thoughts about swivels vs Shackles? If the Ultra swivel is the best I'll go with it, but might go hungry for a week...LOL

[Dockhead]

Originally Posted by Matt sachs

I liked the Ultra Swivel, until I looked at the price. Any thoughts about swivels vs Shackles? If the Ultra swivel is the best I'll go with it, but might go hungry for a week...LOL

The best swivel (see testing on the Cox Engineering) site is the Kong.

But a swivel is a potential weak point. I used the jumbo Kong swivel with my previous anchor, a 121 pound Rocna. Swivel was necessary because the Rocna was balanced to come up upsidedown, but was a PITA - hung up on the bow roller, besides being a potential weak point.

I replaced to Rocna with a Spade, which has lead ballast and so is much better balanced. I got rid of the swivel and substituted a Wichard concealed-pin shackle. What an amazing improvement!

Don't use a swivel unless you really need it.

[Matt sachs]

Thanks Dock. Swivels kinda scare me

[Dockhead]

Originally Posted by Matt sachs

Its here! woo hoo!, yes Im a nerd. 400 ft of G4. Now...where to cut it? should I put 300 ft on one side and 100 on the other? 200 on each side?

Don't keep two chain rodes in the bow - don't want the weight up there. I have 100 meters (330 feet) of 1/2" chain and regret it - will reduce it or switch to 10mm G70 this spring.

If I were you, I would cut off as much as you really need for 5:1 in the deepest water you think you will anchor, and add rope for the off chance you need more. Use rope for the secondary anchor, with 10 meters or so of chain leader, and sell the excess chain.

That's assuming your anchor locker is upon the forepeak like mine is. Weight in the bows really hurts pointing ability, and keeps the bows from rising to the seas, giving you a wet deck.