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Old 19-02-2020, 11:32   #16
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Re: 8mm spectra goes BANG. Sun degradation?

Two years ago we shifted much of our running rigging to Amsteel, including our halyards, running backstays, check stays, and lifelines. All together we saved about 150 lbs, most if it aloft.

Our halyards were tapered, meaning that we stripped the cover off except where it might be on the sheet stoppers. They are 6mm dyneema with normal polyester covers where needed.

After about one year the jib halyard broke suddenly about 1 foot from the Brummel splice at the shackle, just below the halyard sheave, while sailing; a flat, clean, break. We hadn't had a halyard break for so many years that I can't even remember when it last happened.

This shocked us, not for the least of which because I had been in the habit of going aloft on a single halyard (not ever again).

This has shaken my confidence in dyneema (or spectra). If a 1 year old dyneema halyard can break at about 10% of its rated strength, then we cannot trust them. I'll still use them, but I consider them a bit suspect.

We probably should worry about the lifelines too.
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Old 19-02-2020, 11:46   #17
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Re: 8mm spectra goes BANG. Sun degradation?

If it was a spliced section with the cover removed from a previous use that failed almost guaranteed it was UV damage accumulated over a long long time.
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Old 19-02-2020, 11:52   #18
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Re: 8mm spectra goes BANG. Sun degradation?

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Originally Posted by Hartleyg View Post
This is true, but only for the first two years or so - after that, the degradation proceeds, but at a slower rate. See this: https://dynamica-ropes.com/wp-conten...SM-Dyneema.pdf
This is interesting... It's been ages since I've followed the topic closely, but in the climbing world I've seen recommendations to replace Dyneema slings after only 3-5 years of use.

Quote:
Originally Posted by wingssail View Post
After about one year the jib halyard broke suddenly about 1 foot from the Brummel splice at the shackle, just below the halyard sheave, while sailing; a flat, clean, break. We hadn't had a halyard break for so many years that I can't even remember when it last happened.
We found a core shot in a jib halyard the other week, also about a foot above the shackle. Weaknesses of Dyneema that could be relevant are temperature and stress concentrations (knots, bends).
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Old 19-02-2020, 12:53   #19
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Re: 8mm spectra goes BANG. Sun degradation?

Both of those halyard failures are interesting. One a year old line which should have close to 90% of original strength. No indication how old the other line was.

But that would indicate to me once again some type of manufacturing defect.

Not an encouraging prospect.

When cables are made, and also when rope is made, there are spoils of wire that fit on a disk. The wires run through blocks and then dies to form them into the cable. As the wires pay out the spoils need to turn at an appropriate rate so that the twist in the wire is worked out. With braided rope it’s more complicated because got have some strands running counter to others and then they cross cross. But the spoils still have to spin so as to take out the twist.

If you don’t you get hockels, or “Ass holes” to the more crusty crowd. And if you pull them tight then you ruin the strands, they become severely weakened. I’ve run continuous 10 mile sections of fiber cable off a reel and to ou need to be very careful handling the cable to not allow hockles to develop. The cable needs to be handled into and out of figure eight loops to even out the twist.

So if some of this strand spools were to lock up and not spin correctly then the strands will develop hockles and be severely weakened. If it’s in a braided construction, and this is speculation, it might be able to capture adjacent threads in the hockle and compromise them. Further it will shorten some strands so that they take a disproportionate amount of the stress. If these short strands break then the stress will be transferred to the remaining strands which would then fail.

All the above being said that can see these process happening at some significant proportion of the roles breaking strength but not at the relatively low loads we are discussing here. IMHO it’s pretty hard to put even 500 pounds of load on a halyard.

So I offer this explanation for consideration. Not as a guaranteed reason for the failures.

It would be most interesting to know if all these lines came from the same factory. Frankly these are extremely unacceptable failures.
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Old 19-02-2020, 13:04   #20
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Re: 8mm spectra goes BANG. Sun degradation?

I should clarify, in my case it was the sheath that was abraded through, with the core still intact but poking out. I though it interesting that someone else had a failure in a similar spot. With a clean break my assumption would be a line loaded over an edge, here I suspected a rub point.
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Old 19-02-2020, 14:24   #21
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Re: 8mm spectra goes BANG. Sun degradation?

Quote:
Originally Posted by Simi 60 View Post
.Lifting our 320kg - 700lb dinghy out of the water
8mm spectra at either end - 5000kg breaking strain.

Lifting the outboard end and BANG
That end of the dinghy drops 3ft back to the water.

8mm spectra was the inner core from a 10mm halyard off of a previous vessel we had.
It was probably 15 years old but was in good condition when replaced after a couple of years and had only had the outer case removed and put into service as a winch rope 3 years ago. Prior to that it was sitting in the garage doing nought.
Given the strength of rope to dinghy weight, even if old I would have thought it more than up for the job.

I can grab bits of it at the break and pull out tufts of fiber several inches long.

Sun degradation???????????

Decision now is do I replace with same same but new?
Or do I go old school and use 8mm double braid - nowhere near as strong but it does have that outer case for UV protection if, that was the problem

===


For what it's worth, I once spoke with the captain of a megayacht that was towing a 26 ft center console as a dinghy. They were towing with 12 mm Dyneema and said they needed to replace it every three years.
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Old 19-02-2020, 15:54   #22
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Re: 8mm spectra goes BANG. Sun degradation?

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Originally Posted by wingssail View Post

After about one year the jib halyard broke suddenly about 1 foot from the Brummel splice at the shackle, just below the halyard sheave, while sailing; a flat, clean, break. We hadn't had a halyard break for so many years that I can't even remember when it last happened.

This shocked us, not for the least of which because I had been in the habit of going aloft on a single halyard (not ever again).

This has shaken my confidence in dyneema (or spectra). If a 1 year old dyneema halyard can break at about 10% of its rated strength, then we cannot trust them. I'll still use them, but I consider them a bit suspect.

We probably should worry about the lifelines too.
Shocked me to.
And I to had gone up on that halyard several times in the past, but at least had another halyard attached.

Glad it happened in an anchorage and not when we were on passage.

For this application I think I am going back to old skool 8mm double braid, just need to figure out the splicing.
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Old 19-02-2020, 16:10   #23
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Re: 8mm spectra goes BANG. Sun degradation?

I have seen spectra cored halyards break without warning under low load, even when the cover looked perfect.

The culprit was the rope clutch. The inner fibers were crushed and broken. They do not like a tight bend, or crushing.

After I saw that, I changed our policy. None of the service staff went up a mast on a cored line--ever. You can not visually inspect them for strength. Even though it is "weaker" dacron double braid is safer. You can inspect the outer braid and be confident that the line is undamaged.

Spectra or dyneema can be safely used for lifting and hoisting, but only single braid so you can inspect it. For many applications, that is not practical because they are so slippery.
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Old 20-02-2020, 08:00   #24
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Re: 8mm spectra goes BANG. Sun degradation?

I've learned a bit about exotic rope from reading this thread, and thank you. But, getting back to Simi 60's original problem, he's using 8 mm+ blocks to lift a 700# dinghy. 3/8" three stand nylon rope has a tensile of 3,300#, it is easy to splice, probably would fit those blocks, and you never have to worry about any of the problems discussed herein. If not, 5/16 would do the job. That's as old school as you can get without switching to Manila hemp, but for this job it's fine.
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Old 20-02-2020, 08:08   #25
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Re: 8mm spectra goes BANG. Sun degradation?

Quote:
Originally Posted by billknny View Post
I have seen spectra cored halyards break without warning under low load, even when the cover looked perfect.

The culprit was the rope clutch. The inner fibers were crushed and broken. They do not like a tight bend, or crushing.

After I saw that, I changed our policy. None of the service staff went up a mast on a cored line--ever. You can not visually inspect them for strength. Even though it is "weaker" dacron double braid is safer. You can inspect the outer braid and be confident that the line is undamaged.

Spectra or dyneema can be safely used for lifting and hoisting, but only single braid so you can inspect it. For many applications, that is not practical because they are so slippery.
The rope clutch explanation is a good one if the above broken ropes were exposed to a clutch.

Thatís why I asked the OP to chop up his remaining line into 6Ē pieces, to see if the problem is related to a short piece, in a particular spot or all over. If itís UV it will be widespread.

I wonder if a highly loaded soft shackle across a rather narrow load edge, like a ring. Would suffer the same problem?
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Old 20-02-2020, 08:42   #26
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Re: 8mm spectra goes BANG. Sun degradation?

I'll leave this here, in case it's useful. (Deeper in it discusses chafe, UV, sharp bends, etc.)

https://www.ussailing.org/wp-content...n-Jan-2014.pdf

Quote:
Originally Posted by hpeer View Post
I wonder if a highly loaded soft shackle across a rather narrow load edge, like a ring. Would suffer the same problem?
I'm always nervous about loading soft goods over edges. The link above mentions that a 1:1 ratio of bend radius to line diameter results in a 50% loss of strength, which is one reason in addition to slippage that one must be careful with knots in such lines.
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Old 20-02-2020, 12:12   #27
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Re: 8mm spectra goes BANG. Sun degradation?

SK75 dyneema if going to a captive winch is the best rope for the job. Will be obviously fuzzy well before failure at these loads. Who knows what the original line actually was and any pics of condition?
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Old 23-02-2020, 13:10   #28
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Re: 8mm spectra goes BANG. Sun degradation?

Quote:
Originally Posted by billknny View Post
I have seen spectra cored halyards break without warning under low load, even when the cover looked perfect.

The culprit was the rope clutch. The inner fibers were crushed and broken. They do not like a tight bend, or crushing.
.
Interesting
We did have rope clutches for the halyard but it "should" never have been fully loaded as rope came through clutch, around winch and to horn cleat.
Going back a while but 99% sure I always left the mainsail halyard, which this was, backed up on the cleat and eased the clutch.
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Old 23-02-2020, 13:16   #29
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Re: 8mm spectra goes BANG. Sun degradation?

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SK75 dyneema if going to a captive winch is the best rope for the job. Will be obviously fuzzy well before failure at these loads. Who knows what the original line actually was and any pics of condition?
It all looked like the upper right section except for a couple of hundred mm around the break that looked a bit furrier like the lower left section.
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Old 23-02-2020, 14:09   #30
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Re: 8mm spectra goes BANG. Sun degradation?

Quote:
Originally Posted by billknny View Post
I have seen spectra cored halyards break without warning under low load, even when the cover looked perfect.

The culprit was the rope clutch. The inner fibers were crushed and broken. They do not like a tight bend, or crushing.

After I saw that, I changed our policy. None of the service staff went up a mast on a cored line--ever. You can not visually inspect them for strength. Even though it is "weaker" dacron double braid is safer. You can inspect the outer braid and be confident that the line is undamaged.

Spectra or dyneema can be safely used for lifting and hoisting, but only single braid so you can inspect it. For many applications, that is not practical because they are so slippery.
Bilknny, I'd point out that double braid dacron is a "cored" line. I am not sure how an inspection of the cover of a double braided line tells you anything about the condition of the core.

Further, the failure of our dyneema halyard was a single braid 6mm line, no cover, and it looked fine prior to the failure.

Finally, it was never subjected to a rope clutch where it broke, and the sheave where it passed was 4" diameter, AND there is a guard at the sheave box to protect the halyard from being loaded against any edge or sharp turn.

So my conclusion is that dyneema can fail, even lightly loaded, and it is not always possible to predict where or when.

I have never had double braided dacron lines fail like that, and even then, the cover is often strong enough to support ordinary loads.

I did once, many years ago, have a double braided line with a Kevlar core fail and on inspection we found that the core had shattered into six inch sections, at many places. This was 1/2 Kevlar line used for a spinnaker guy. I believe that the cover had been supporting the load for awhile.

So I agree, it's better to have a single braid line than one where the strength is in a core which you cannot see.
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