Dyneema broke at cover taper

[Bill_Giles]

6mm seems very thin for a vital halyard on a 43’ boat. I’d only go that small if I were a highly competitive racer looking to save every ounce (or gramme) aloft. Especially with a taper.

[twofingerpoi]

Agreed that 6mm seems quite thin. My Beneteau 361 was originally spec'ed for 12mm halyards but that binds in the sheaves, so especially with Dyneema I am using 10mm which runs nicer in the sheaves, is stronger and still has a nice hand. I use Samson MLX3.

[Cheechako]

Originally Posted by sailingharry

in the winter of 21/22, I made a new main halyard for my 43' sailboat. I made it of "6mm dyneema." Unfortunately, it was Chinese (AKA "Chinema") although our Thinwater says Chinema actually tests fairly well. But more importantly, the "6mm" was really 5mm (or maybe a touch less). Still, it should have been adequately strong. At the end of 2023, it broke. Replacement dyneema is inbound from Miami Cordage, 6mm (she promises!) from a US mill. $0.65/ft for 6mm, about double the Chinema, available only in blue. Haven't seen it yet, no opinions yet.

So, my problem/question.

I built this of bare dyneema cord. I covered areas where it is winched/clutched, no problems there. And I covered the top 5' or so with a dyneema chafe cover. Where the cover ended is where the break occurred. I already "knew what I was doing" (in quotes, 'cause now I don't know....), so didn't do any research this time (not my first forray into this kind of work), but I found a link today that is mostly what I did:

The biggest difference is this video pushed the entire cover into the core in one piece, I de-braided it, split it in 3 sections, and buried/tapered each 1/3 section. I also did a sewn whipping just like he demonstrates.

So my first thought was my burying the cover into the core made a stress concentration. If you think about it, it is identical to terminating the tail of a splice with no taper (actually, worse, as it enters from the side). But if this is the normal way to finish the cover on a stripped end of covered dyneema, then I did nothing wrong.

So, shame me. Tell me the errors of my ways. Make me slink away. I want to know if I did something wrong!

Picture below. The upper part shows the covered portion. It terminates in a whipping, and then you see the "debraided" dyneema cover. The lower part is the bare dyneema.

How in the world do you handle a line that small?

[sailingharry]

Originally Posted by Cheechako

How in the world do you handle a line that small?

Oh, I don't much handle line that small. On my jib halyards, yes, but they only go up once a year. On the main, the most of the handled part is covered (and at clutches, additional core inside too). So, on a 130' line, the first 70' (from the shackle on deck, up to the top and down about 20') is bare Dyneema. Then about 40' (the amount needed hoist the sail, including all the reefs/etc) is covered/cored. Then the last 20' is bare again, as this is used as tail, initial hoist, etc and easy to handle even at 6mm or 1/4". So the part that I actually "handle" is between 3/8 and 1/2" diameter.


This approach yields much higher returns in other lines. My third reef clew, for instance, is probably 100' long, maybe more, and only about 10' has cover on it. My jib halyards, around 110', have about 10' of cover. Spin sheets, around 80' each, have about 15' of cover.

[sailingharry]

I wanted to post a little (or not so little...) followup. I'm an engineer, and numbers fascinate me. Simply "you get what you pay for" or "go mainstream" doesn't do anything for me -- numbers do. So I have some numbers, and it's great stuff.


First, I realized that "diameter" is a really, really hard number to measure. The line is soft, it squeezes, it bunches, and you are trying to measure to 1/10 of a mm. What really matters is "material in play" -- or lbs/100ft. Assuming the material is all the same (yes, that's an assumption), then lb/100ft should directly correlate to breaking strength. This is clearly seen in the Marlow SK-75 spec table, where as the diameter increases 1mm at a time, the incremental strength and weight are not at all consistent -- some 1mm increases are huge, some are tiny (yes, I know it's not linear -- it's a square -- but that's not the issue). As an example, Marlow lists 6mm as 1.19 lb/100 ft and 9129lb, and 7mm as 1.88 lb/100ft and 14,032 lb -- a 36% increase in cross sectional area yields a 58% increase in weight and 54% increase in strength.


So I broke out my tape and scale, and have some numbers. All my product was listed as "6mm."



First, my original Chineema, that I was very happy with, was 1.42 lb/100ft
My new crap Chineema is .97 lb/100ft -- well crap, that explains it!
NE SK75 claims to be 1.7 lb/100ft, yielding 12385 lb (7285 lb/(lb/100ft))
Marlow 6mm claims to be 1.19/100ft, yielding 9129 (7671 lb/(lb/100ft))
Marlow 1/4" (listed as 7mm) claims to be 1.88/100ft, yielding 14022 (7458 lb/(lb/100ft))
Amsteel Blue claims to be 1.6 lb/100ft, yielding 8600 lb (5375 lb/(lb/100ft))
Amsteel claims to be 1.4 lb/100ft, yielding 7400 lb (5285 lb/(lb/100ft))
AND
Miami Cordage Ironlite is measured at 1.49 lb/100ft, yielding 7940 (5328 lb/(lb/100ft)) (an odd note, the published weight is an obviously wrong 2.70 lb/100ft).


So.... drum roll here. The are some interesting conclusions.
The first, and most significant, is that you should straight up ignore "diameter" when buying dyneema. Use strength (or lb/100ft).
The second is that there are some consistent inconsistencies here. Within a brand (say, Marlow), the strength/weight relationship is very strong. And between some vendors (Marlow and NE, or Amsteel and Miami) the numbers are close. But I can't understand (or perhaps believe?) that Marlow and NE are about 50% stronger for a given weight than Amsteel Blue!
And, given that diameter is a very low value metric, price comparison is really hard (you need to pick a "strength class" and compare, or perhaps calculate $/strength as your metric).


One final conclusion -- my Miami Cordage 6mm was $0.66/ft (with reasonable shipping), and compares nicely to the same size Amsteel at 2-3 times the price. They also sold me some really nice 8-plait nylon for a new snubber. I'm pretty sure the woman who answered the phone and took my order was the owner of the company!

[thinwater]

The standard rope measurement method measure the diameter while under 5% of MBS. This eliminates most of the variability in softness you mentioned. For the ropes you were comparing, that would be 250 pounds.


Yes, weight is good too.


Another method, if you don't have the gear to breaks stuff a 5000#, is to pull one stand and break that. Good for used ropes too.


A difference that weight and measurements does not take in is UV resistance, coating effectiveness, and how that relates to wear. I have used Amsteel and Chineema of equal strength side by side, and the Amsteel wears better over time. I'm guessing the difference is UV and coating related.

[s/v Jedi]

A major difference for Samson Amsteel Blue is that it’s the gold standard for single braid Dyneema.

First of all, it’s made from Dyneema, as in the original fiber made by the Dutch company DSM. It’s not a knockoff like the ones that are reported to fail quickly regularly here on CF.

Second, it has the Samthane coating. We recently replaced our running backstays which were 19 years old. They did show deterioration from UV exposure but not a sign of pending failure. Shame we couldn’t find a way to test them, but replaced with the exact same 10mm Amsteel Blue.

Third, Amsteel Blue has been verified by ABS and is type approved by all relevant organizations incl. ABS and Lloyd’s. This is required for applications like mooring ships etc.

For tensile strength, would the weight difference explain the strength difference between Amsteel and Amsteel Blue? I don’t think the coating is a significant part of total weight so we could assume weight is all the actual fiber.

[Benz]

Originally Posted by sailingharry

I wanted to post a little (or not so little...) followup. I'm an engineer, and numbers fascinate me. Simply "you get what you pay for" or "go mainstream" doesn't do anything for me -- numbers do. So I have some numbers, and it's great stuff.


First, I realized that "diameter" is a really, really hard number to measure. The line is soft, it squeezes, it bunches, and you are trying to measure to 1/10 of a mm. What really matters is "material in play" -- or lbs/100ft. Assuming the material is all the same (yes, that's an assumption), then lb/100ft should directly correlate to breaking strength. This is clearly seen in the Marlow SK-75 spec table, where as the diameter increases 1mm at a time, the incremental strength and weight are not at all consistent -- some 1mm increases are huge, some are tiny (yes, I know it's not linear -- it's a square -- but that's not the issue). As an example, Marlow lists 6mm as 1.19 lb/100 ft and 9129lb, and 7mm as 1.88 lb/100ft and 14,032 lb -- a 36% increase in cross sectional area yields a 58% increase in weight and 54% increase in strength.


So I broke out my tape and scale, and have some numbers. All my product was listed as "6mm."



First, my original Chineema, that I was very happy with, was 1.42 lb/100ft
My new crap Chineema is .97 lb/100ft -- well crap, that explains it!
NE SK75 claims to be 1.7 lb/100ft, yielding 12385 lb (7285 lb/(lb/100ft))
Marlow 6mm claims to be 1.19/100ft, yielding 9129 (7671 lb/(lb/100ft))
Marlow 1/4" (listed as 7mm) claims to be 1.88/100ft, yielding 14022 (7458 lb/(lb/100ft))
Amsteel Blue claims to be 1.6 lb/100ft, yielding 8600 lb (5375 lb/(lb/100ft))
Amsteel claims to be 1.4 lb/100ft, yielding 7400 lb (5285 lb/(lb/100ft))
AND
Miami Cordage Ironlite is measured at 1.49 lb/100ft, yielding 7940 (5328 lb/(lb/100ft)) (an odd note, the published weight is an obviously wrong 2.70 lb/100ft).


So.... drum roll here. The are some interesting conclusions.
The first, and most significant, is that you should straight up ignore "diameter" when buying dyneema. Use strength (or lb/100ft).
The second is that there are some consistent inconsistencies here. Within a brand (say, Marlow), the strength/weight relationship is very strong. And between some vendors (Marlow and NE, or Amsteel and Miami) the numbers are close. But I can't understand (or perhaps believe?) that Marlow and NE are about 50% stronger for a given weight than Amsteel Blue!
And, given that diameter is a very low value metric, price comparison is really hard (you need to pick a "strength class" and compare, or perhaps calculate $/strength as your metric).


One final conclusion -- my Miami Cordage 6mm was $0.66/ft (with reasonable shipping), and compares nicely to the same size Amsteel at 2-3 times the price. They also sold me some really nice 8-plait nylon for a new snubber. I'm pretty sure the woman who answered the phone and took my order was the owner of the company!

One variable I don't see is what SK or AS variety of Dyneema you're using to measure. The original Amsteel Blue was SK75 (or AS75, as they called it), and I don't know whether they've upgraded to the now most-popular SK78, which is stronger. SK75 is now only commonly used for cheap cores, blended cores or for pre-stretching, like Dinyce Dux. Then there's SK99 (the strongest so far), and DM20, the least creepy. So within the same brand, 6mm might have 8 varieties (each sort plain, and each sort pre-stretched), each with different break loads. And the difference in diameter between the same line plain and pre-stretched is visible to the eye.
Lbs/foot can only be a useful comparison if comparing the same sort, and will surely be skewed by the weight of the solids in various coatings. Some lines have NO coating, others have silicone, others vary in thickness--it's an unknowable variable. Also, the angle of the braid will affect the weight, since more winding per inch results in more material. That's how Maffioli gets their Ultrawire so strong: a very loose braid so more material travels less far while keeping the diameter down.
I do wholeheartedly agree that engineering MUST be done with published data, not with how something looks.

[sailingharry]

Originally Posted by s/v Jedi

For tensile strength, would the weight difference explain the strength difference between Amsteel and Amsteel Blue? I don’t think the coating is a significant part of total weight so we could assume weight is all the actual fiber.

I was actually a bit puzzled by some of the results. My ultimate calculation resulted in (lb breaking strength) per (lb/100ft). This is a really convoluted unit, but is basically a Strength/size number. One would expect this to be a very consistent number, especially for a given fiber/construction. The two oddities:


Amsteel was 5285, vs Amsteel Blue at 5375, making Amsteel Blue less than 2% stronger than Amsteel -- or, a rounding error. I somehow would have expected more.


Amsteel is the "gold standard" as you point out. How come, then, does my research show that Amsteel is ~5300 and NE Ropes and Marlow are closer to 7500, or 40% stronger? Am I reading different numbers (average vs min, for instance)? Whatever attributes may be assigned to "genuine" etc, Samson, NER, and Marlow are certainly not going to be cutting corners, watering down product, mis-stating diameters, etc -- they are all top tier manufacturers.

[s/v Jedi]

Originally Posted by sailingharry

I was actually a bit puzzled by some of the results. My ultimate calculation resulted in (lb breaking strength) per (lb/100ft). This is a really convoluted unit, but is basically a Strength/size number. One would expect this to be a very consistent number, especially for a given fiber/construction. The two oddities:

Amsteel was 5285, vs Amsteel Blue at 5375, making Amsteel Blue less than 2% stronger than Amsteel -- or, a rounding error. I somehow would have expected more.

Amsteel is the "gold standard" as you point out. How come, then, does my research show that Amsteel is ~5300 and NE Ropes and Marlow are closer to 7500, or 40% stronger? Am I reading different numbers (average vs min, for instance)? Whatever attributes may be assigned to "genuine" etc, Samson, NER, and Marlow are certainly not going to be cutting corners, watering down product, mis-stating diameters, etc -- they are all top tier manufacturers.

The small differences are either rounding numbers / inaccuracies or the difference between sk75 and sk78. The big differences are between sk75/78 and sk99, which is much stronger.

Amsteel Blue higher price than Amsteel is mostly because of their type certification I think. But for things like running backstays etc. it’s nice to know you have a certification product holding the mast up

The sk99 products are irrelevant for cruisers. Sk75 is simply good and light enough. I see most cruisers using Amsteel one or two sizes bigger than required. I don’t do that because I do my own rigging work so don’t have to pay someone replacing it more often. But with so many years on my 10mm backstays the deal has become mind blowing. The difference for running backstays is a no brainer as the heavy steel wire ones, when retracted forward, always swing back and forth and around the spreaders. After changing to Dyneema this never happened again.

Same with halyards. We had the half wire/ half rope type for the jib and within a year there was a broken strand. And the main halyard stiff and still stretching.

Edit: Amsteel Blue used to be sk75 but there was documentation indicating a change to sk78. They have since removed all mention of fiber type and I think regular Amsteel may still be sk75. Another possibility is that Amsteel is imperial sized while Amsteel Blue is metric, explaining weight difference. They have the same coating, but available colors are a bit different. I like to buy blue because it isn’t available as regular Amsteel so they can’t cheat me ;-)

[Benz]

Originally Posted by sailingharry

I was actually a bit puzzled by some of the results. My ultimate calculation resulted in (lb breaking strength) per (lb/100ft). This is a really convoluted unit, but is basically a Strength/size number. One would expect this to be a very consistent number, especially for a given fiber/construction. The two oddities:


Amsteel was 5285, vs Amsteel Blue at 5375, making Amsteel Blue less than 2% stronger than Amsteel -- or, a rounding error. I somehow would have expected more.


Amsteel is the "gold standard" as you point out. How come, then, does my research show that Amsteel is ~5300 and NE Ropes and Marlow are closer to 7500, or 40% stronger? Am I reading different numbers (average vs min, for instance)? Whatever attributes may be assigned to "genuine" etc, Samson, NER, and Marlow are certainly not going to be cutting corners, watering down product, mis-stating diameters, etc -- they are all top tier manufacturers.

Mis-stating diameters is an everyday thing. Look at any 6mm from four different manufacturers and even from different products within the same brand and you'll see that diameter is a nominal, not an actual, thing to them.
The only thing to go by, I say again, is published data--and even that data is skewed by whether it's tested while spliced or not, which is harder to find out.

[sailingharry]

Originally Posted by Benz

Mis-stating diameters is an everyday thing. Look at any 6mm from four different manufacturers and even from different products within the same brand and you'll see that diameter is a nominal, not an actual, thing to them.
The only thing to go by, I say again, is published data--and even that data is skewed by whether it's tested while spliced or not, which is harder to find out.

Which furthers my assertion that WEIGHT is the most useful metric. You still need to suss out 75/78 vs 99 (some products are even mixtures, I think some even with polypropylene!*), as Jedi points out, but weight/100ft is the real metric of what you are buying. As Thin points out, lots of data can be gathered when in hand (actual loaded diameter, weight, breaking strength, etc), but that doesn't work for shopping. Within a fiber (75/78, 99, PBO, or even Dacron/Nylon, etc), weight is what provides the material to provide the strength. The coating skews it slightly. It's MUCH harder (ie, intentional deceit) to fudge the weight than the diameter. Even the break strength is open for debate -- as you point out, spliced or not. Even words like "average" or "minimum" or "ultimate" or "working" can cause problems -- while they are all real, meaningful words, it's easy to skip past the modifier and go straight to "strength."


* Just to be clear, I'm not saying the mixtures are bad. They are clearly marked as such and fit for purpose. My inside jib sheet, a very highly loaded line on a high aspect sail, came to me with one of those (PhD, I think, Dyneema/Dacron blend) that is high strength, low stretch, but has a wonderful hand and works well in the winch and clutch.

[sailingharry]

Originally Posted by s/v Jedi

The small differences are either rounding numbers / inaccuracies or the difference between sk75 and sk78. The big differences are between sk75/78 and sk99, which is much stronger.

Your comment got me to go revisit my numbers. That big anomaly in NER is (sort of) wrong. The numbers I pulled are the Heat Set SK75, and while I wonder how the heat set gives a 505% increase, it's clearly not the same as regular SK75. They still other SK78 (STS-78, and Endura 12) that falls right in with the other two lower strength products (Amsteel and IronLite).


The Marlow specs further my comment above about trying to read "strength" as a spec. Marlow lists on their web page for the product line for D12 6mm a min strength of 3140 and average of 3490kg. But on their PDF, linked right from that page, that provides full detail, they list minimum linear strength (ISO 2307) at 4150. I used the 4150 in my calculations, using 3140 yields 5187 lb/(lb/100ft), right in line with everyone else. A curious tidbit, all the numbers on their SK75/78 line sheet are IDENTICAL to their SK99 line sheet, sounds like a typo!


And speaking of typo's, Miami Cordage responded to my question about their weird listed weight for IronLite, and thanked me for noting their typo.

[Benz]

Originally Posted by sailingharry

Your comment got me to go revisit my numbers. That big anomaly in NER is (sort of) wrong. The numbers I pulled are the Heat Set SK75, and while I wonder how the heat set gives a 505% increase, it's clearly not the same as regular SK75. They still other SK78 (STS-78, and Endura 12) that falls right in with the other two lower strength products (Amsteel and IronLite).


The Marlow specs further my comment above about trying to read "strength" as a spec. Marlow lists on their web page for the product line for D12 6mm a min strength of 3140 and average of 3490kg. But on their PDF, linked right from that page, that provides full detail, they list minimum linear strength (ISO 2307) at 4150. I used the 4150 in my calculations, using 3140 yields 5187 lb/(lb/100ft), right in line with everyone else. A curious tidbit, all the numbers on their SK75/78 line sheet are IDENTICAL to their SK99 line sheet, sounds like a typo!


And speaking of typo's, Miami Cordage responded to my question about their weird listed weight for IronLite, and thanked me for noting their typo.

The whole point of heat-setting is to increase strength: SK75 gains the most benefit from the process; the others gain some strength, but the gap between heat-set and not is most marked with 75. Also, heat-set has more fibers per diameter, since the bundles are fully compressed in the process, so a 6mm line may become 5mm.
Rather than weigh each product I want to use, I'll just go with the published engineering specs, and factor in whatever safety margin I need. Seems simpler.

[s/v Jedi]

Yes, heat setting reduces the diameter. Splicing it introduces constructional elongation again but the improvement on creep is permanent.

I use Samson MLX-3 for my main and jib sheets and want to switch to it for my mizzen sheet as well. I go one size down with it, using 10mm for jib (51 m^2)and mizzen (49 m^2) and 12mm for the main (65 m^2).

This season I got to observe the difference this makes for the jib in light weather performance and it is remarkable. I had been using a 5/8” Regattabraid before!

MLX-3 is a Dyneema + polyester blended core with polyester cover. It’s stiffer than the standard XLS-3 double braid polyester but still has a very nice hand. You get most of the Dyneema benefits for a lower price. The core has the Samthane coating in matching color so you can strip the cover where it isn’t needed, which I didn’t do yet.