Dyneema broke at cover taper

[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:

https://www.youtube.com/watch?v=x62B...l=PremiumRopes

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.

[thinwater]

a. I said that the Chineema I tested did reasonably well, meeting the claimed specs. However, those were just a few Amazon deals, so who can say what the quality control on another vendor might be. I would not use Chineema on a halyard; too much of a PIA if it fails.


b. In a 5-year follow up article (Practical Sailor) I noted that the Chineema was noticeably more chafe-prone. No failures.


c. I understand that failure point would be in the sun at the dock. But it dod not look chafed or sunburned.


d. The failure at the whipping is suspicious. Also, I notice red dye transfer from the whipping cord to the Dyneema core. That suggests there were quite a few stitches through the core at the crossover point. Not good.


I wonder if you used a sharp needle, and if the needle cut some strands in the process of whipping. That maybe one cause. 5mm Chineema is also a little small for this size boat.


Was there lock stitching? I'm not seeing it. It may not matter much at this junction, but if you want to hold a cover in place near a winch it is far more secure.



I never whip the cross over. No need and it is a wear point and a potential weakening point. The splice should be held by lock stitching on both sides of the splice. The stitching should be made with a dulled needle that cannot cut fibers. You want to work it between the fibers. See Samson instructions. The needle work in the video is poor practice. Too many chances to damamge the core. It looks good, but can be weak, as you have learned.


The other problem with securing the cover with a whipping like that is that ALL of the sliding stresses are concentrated at one point, instead of distributed like lock stitching. The stress riser is so great ... there wasn't much point in tapering t he ends.


Skip the whipping and lock stitch instead next time.



BTW, a polyester cover is fine for mos applications.

[s/v Jedi]

I only use the big names, mostly Samson. I just replaced my 3/8” Amsteel Blue running backstays, which still performed good enough… I had installed them in 2005 !

[sailingharry]

Thin,


Thanks for the feedback! I hope I didn't terribly misquote you -- I did say it tested "fairly" well.


My whipping was with a fairly thick whipping twine with a red coloring that transferred, as you noted. I love whipping, only sewn, and do a good job. Which means 4 sewn passes (12, 3, 6, and 9 o'clock), twice around. And use a nice sharp needle. Perhaps it's a really nice way to whip the end of a nylon 8-plait, but not so good in the middle of a piece of dyneema! LOL.


I agree, neither sun nor chafe make sense. This is the end of the halyard (at the shackle), so not much opportunity for chafe. And at 2 years old, sun shouldn't be an issue.


Two years before, I ordered 6mm from the same firm. It is a true 6mm, and my two jib halyards (Solent rig) are essentially identical, and have given me no cause for concern. And the first order was 1/2 the cost of the crappy second order! I'm not a happy customer any more, and they won't get a chance to change my mind.


I do cover (and add a thin cord with tapered ends in the center for additional thickness) at winches and clutches. Your suggestion about lock stitch vs whipping is noted.

[Benz]

It is necessary to taper the tail of the dyneema cover. The longer the tail, and the more gradual the taper, the better. You don't need to comb all the strands loose (it looks like that is the picture)--just pluck eight strands out of the braid to cut off, move along a few inches, pluck eight more, and so on.
Stitching crossovers is very good. Whipping is also OK if you don't go overboard.
Name-brand dyneema is worth the extra cost, IMO. You never know the quality of chinese brands.

[Breaking Waves]

Originally Posted by sailingharry

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.

Just to be clear - Is that a picture of the break - eg the red stained top end broke off under the whipping?

If so, it is a very unusually clean break. Likely caused either by some significant cutting filament breaking (from the stitching needle?), or a really focused stress riser - did you pull the stitches quite tight over a short area? That can distort the braid and create such a stress riser.

Depending how you did it, the cover bury could create a 20% strength loss stress riser (up to 50% if you did it in a way that distorted a lot of the braid load path - but I have never seen that big a loss in any test I have done, 20% more likely if you were at all careful/gentle).

Given how clean that break is, I am also sort of wondering if that exact spot was resting on an undersized sheave or pulled onto the edge of the halyard slot (would only need a 10 degree deflection to create a problem), or some other 'mechanical' bend on the masthead?

Originally Posted by sailingharry

And at 2 years old, sun shouldn't be an issue.

Well, at two years, you can in fact have some significant strength loss. UV test results are highly variable, depending in the exact rope construction/coatings and the exact environmental conditions, but you would likely have minimum 20% loss and potentially up to max 50% - probably just guess 30% from the range of tests I have seen.


@thinwater:"I said that the Chineema I tested did reasonably well, meeting the claimed specs." Do their 'claimed specs' equal amsteel specs or are they significantly lower. I have notices on a lot of the Chinese soft shackles on Amazon when I break them they do usually meet their stated spec but that spec is a lot lower than one would expect from a properly made soft shackle of good rope.

[s/v Jedi]

It looks like the Dyneema has no coating at all…

[sailingharry]

Originally Posted by Benz

It is necessary to taper the tail of the dyneema cover. The longer the tail, and the more gradual the taper, the better. You don't need to comb all the strands loose (it looks like that is the picture)--just pluck eight strands out of the braid to cut off, move along a few inches, pluck eight more, and so on.
Stitching crossovers is very good. Whipping is also OK if you don't go overboard.
Name-brand dyneema is worth the extra cost, IMO. You never know the quality of chinese brands.

I went overboard on the taper (my time is free and I do it in front of the TV when the admiral picks boring shows). I comb all strands, then split in 1/3, and bury each 1/3. The pull them fully out at the exit point, taper a long taper, and pull back in. The videos I see show to just bury in one tapered chunk. Sure will be easier!


I am puzzled by the need to taper. If taper is good (essential), as we all hear, I understand that. But, it would seem to me that the bury is a "zero length taper." The underlying dyneema is traveling along with nothing in it -- and then in 1/2 diameter, it has the full width of the cover buried inside it -- and worse, it pulls and pushes the strands aside to fit inside! How is that less stressful on the strands than an abrupt termination of the bury at the tail? No, I'm not recommending or wanting to not bury -- I'm just concerned about how sending the cover into the core isn't fatal.


My new line, from Miami Cordage, is in the mail. They "promise" that it is a full 6mm, and the fiber comes from a US fiber mill. They only make blue (which is what I wanted anyway), but I wish they made some other colors. 6mm of US made line at $0.63/ft sounds good to me.

[sailingharry]

Originally Posted by Breaking Waves

Just to be clear - Is that a picture of the break - eg the red stained top end broke off under the whipping?

Yes, it is a very clean break right under the whipping/right where the bury occurs

Originally Posted by Breaking Waves

If so, it is a very unusually clean break. Likely caused either by some significant cutting filament breaking (from the stitching needle?), or a really focused stress riser - did you pull the stitches quite tight over a short area? That can distort the braid and create such a stress riser.

Yes, agreed, VERY clean. I used a sharp needle (Thin has counseld me on that!). I probably pulled them tight -- I like neat and tight!

Originally Posted by Breaking Waves

Given how clean that break is, I am also sort of wondering if that exact spot was resting on an undersized sheave or pulled onto the edge of the halyard slot (would only need a 10 degree deflection to create a problem), or some other 'mechanical' bend on the masthead?

Shouldn't have been related to mechanical stress. It is 3' from the halyard shackle (the entire purpose of this cover was to provide chafe protection on the halyard at the fully up position). In use, it should pass smoothly over the halyard sheave (this is a 1998 boat so has never seen wire) and be happily laying inside the mast. It also should not be near the masthead in any reef position.

Originally Posted by Breaking Waves

Well, at two years, you can in fact have some significant strength loss. UV test results are highly variable, depending in the exact rope construction/coatings and the exact environmental conditions, but you would likely have minimum 20% loss and potentially up to max 50% - probably just guess 30% from the range of tests I have seen.

This is disturbing. First (as Jedi has pointed out), there is no coating. I've had bad experiences with coated dyneema (from NER) leaving unremoveable stains on sails, gelcoat, and clothing, so I asked for white. I wasn't concerned when I realized "white" meant "no coating" because I was under the assumption that the coating addressed chafe and I have no real chafe concerns here. But if 2 years typically yields 30% loss of strength, what is a realistic life expectancy for uncovered (ie, not double braid) dyneema in applications like halyards, life lines, standing rigging, and any other application where it sees 365 day/year exposure? Was my halyard almost due for replacement anyway, and my jib halyards (two years older) are overdue?[/QUOTE]

[sailingharry]

Originally Posted by s/v Jedi

It looks like the Dyneema has no coating at all…

Yep. As mentioned in the reply I just made, I've had problems with coatings staining, and since I thought (perhaps a lesson learned here...) that the coating addressed chafe which isn't a problem in halyards, that the lack of coating was not a concern. UHMPE, from what I can tell, has a high tolerance for UV. Where "high" is a meaningless relative term....

[Breaking Waves]

Originally Posted by sailingharry

what is a realistic life expectancy for uncovered (ie, not double braid) dyneema in applications like halyards, life lines, standing rigging, and any other application where it sees 365 day/year exposure?

[/QUOTE]


Usually Halyards and standing rigging are quite overstrength because they are being speced for near zero stretch and creep. So they can afford to lose some strength and not be compromised. But you ofc do have a problem in any application where you have tried to cut the strength very near the margin without taking into account the UV loss.

In your case, however, my initial presumption would be (sorry for being blunt) you made a mess of the splice which significantly weakened the rope, and the rope may have been already somewhat at the low end for the application (smaller diameter and Chinese unknown quality). I would think UV not a major factor in this particular break.

Usually, UV damage is signaled by the surface of the rope becoming 'fuzzy' (indicating broken filaments). The photo is small, but I don't see much of that 'fuzzy surface'.

Be gentle with the dyneema when you work it, the #1 strength priority is to go a bit oversized - which will minimize creep and stretch while providing cover for DIY mistakes and sloppiness, and #2 disturb the braid as little as possible in your splices and stitching, don't split strands, don't pull thread tight in a way which takes the strands out of alignment, don't make big bumps or holes in the braid, etc etc. It 100% rewards being smooth and simple and gentle in your work.

[sailingharry]

Usually Halyards and standing rigging are quite overstrength because they are being speced for near zero stretch and creep. So they can afford to lose some strength and not be compromised. But you ofc do have a problem in any application where you have tried to cut the strength very near the margin without taking into account the UV loss.

In your case, however, my initial presumption would be (sorry for being blunt) you made a bad splice which significantly weakened the rope, and the rope may have been already somewhat at the low end for the application (smaller diameter and Chinese unknown quality). I would think UV not a major factor in this particular break.

Usually, UV damage is signaled by the surface of the rope becoming 'fuzzy' (indicating broken filaments). The photo is small, but I don't see much of that 'fuzzy surface'.

First, yes, you are being blunt and insulting my workmanship! LOL. I put it out there so people could be blunt and tell me what I did wrong! I've never been shy when I screw up.



I do tend to agree with your assessment. This line is under 5mm, and the prior batch from the same vendor is 6mm after being in use for years, so the product is clearly inferior. And it is hard to make any conclusion that doesn't impugn my bury, as it broke cleanly at the bury +/- 1mm.


Your assessment on the UV is correct. All of this vendor's line, both the 2 year old and the 4 year old, is still hard and smooth, with no fuzzy.

[thinwater]

Originally Posted by Benz

It is necessary to taper the tail of the dyneema cover. The longer the tail, and the more gradual the taper, the better. You don't need to comb all the strands loose (it looks like that is the picture)--just pluck eight strands out of the braid to cut off, move along a few inches, pluck eight more, and so on.
Stitching crossovers is very good. Whipping is also OK if you don't go overboard.
Name-brand dyneema is worth the extra cost, IMO. You never know the quality of chinese brands.

Unless I am incorrect, it did not break at the taper, it broke at the whipping, where the cover goes into the core. The title is misleading.



You are right about taper and all that, but that is not what broke.

[thinwater]

Originally Posted by Breaking Waves

... @thinwater:"I said that the Chineema I tested did reasonably well, meeting the claimed specs." Do their 'claimed specs' equal amsteel specs or are they significantly lower. I have notices on a lot of the Chinese soft shackles on Amazon when I break them they do usually meet their stated spec but that spec is a lot lower than one would expect from a properly made soft shackle of good rope.

Yes, the spec was lower, perhaps 25% but I don't have it in front of me.


If something meets the spec, it meets the spec. But there is some evidence that it does not hold up as well (visible chafe perhaps related to UV?) over time either. Not sure why. Just what I have observed.

[thinwater]

The coating is a polyurethane, which sticks as well as anything, but it is very hard for ANYTHING to stick to UHMWPE. This is slippery, milk bottle material.



You can refresh the coating with products from a number of rope companies. I have done this and it works, though it is one more maintenance thing. Yale used to sell Maxijacket, but discontinued it due to low volume. Same with Flexdel. Try Marlow or Ino. I have tested those.