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Old 18-02-2020, 22:49   #1
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8mm spectra goes BANG. Sun degradation?

.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
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Old 18-02-2020, 23:24   #2
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Re: 8mm spectra goes BANG. Sun degradation?

Did not break at the knot.
No knot as such, Brummel lock splice at one end and bolted clamp on winch end with multiple wraps before real load is on
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Old 18-02-2020, 23:31   #3
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Re: 8mm spectra goes BANG. Sun degradation?

Yes, old school.
Even standard double braid should be over 1 ton break.
https://www.whitworths.com.au/6mm-d-braid-white
I assume the core you used had no uv stabilisation as it was made to go in a case?
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Old 19-02-2020, 01:28   #4
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Re: 8mm spectra goes BANG. Sun degradation?

Are you sure it was a Spectra/Dyneema core, might have been Vectran - poor UV resistance but really strong. Got a color photo of the fibers?
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Old 19-02-2020, 01:53   #5
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Re: 8mm spectra goes BANG. Sun degradation?

Quote:
Originally Posted by Tin Tin View Post
Are you sure it was a Spectra/Dyneema core, might have been Vectran - poor UV resistance but really strong. Got a color photo of the fibers?
What colour is vectran?

What colour is dyneema/spectra?

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Old 19-02-2020, 01:56   #6
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Re: 8mm spectra goes BANG. Sun degradation?

Usually the core in older lines for dyneema is white fiber and vectran a gold/brown color.


Another way to tell melting point of Dyneema is a lot lower than Vectran
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Old 19-02-2020, 03:52   #7
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Re: 8mm spectra goes BANG. Sun degradation?

Then we have spectra.
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Old 19-02-2020, 05:27   #8
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Re: 8mm spectra goes BANG. Sun degradation?

No expert by far so take with a grain of salt.

I would cut the line into something like 6” pieces, maybe number them to keep the order. Then examine each piece to see if the fault is just in this one spot, if it’s everywhere or if it repeats at some interval.

Do the same with the piece from the bow. Might as well because you don’t trust it now anyway.

I’ve had 8mm life lines on our boat for almost 10 years, no sign of any significant decay. Somewhere I saw the UV decay curve of spectra and it was pretty gradual.

Think about it, some Smart folks are using this stuff as shrouds.

My guess is some kind of manufacturing failure. I once had a case where a brand new electrical Control cable failed upon installation because one of the wire spoils had jammed on the spinning machine when the cable was made. That left some twist in the wire, which made a nickel, which then broke when tensioned. I was able to pin point the location of the break with the cable installed. We then pulled the cable out and I removed the jacket at the point of break. You could see the twist in the grooves in the jacket. It was a big warranty loss for the manufacturer because they could not tell how much bad cable they had.
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Old 19-02-2020, 06:04   #9
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Re: 8mm spectra goes BANG. Sun degradation?

Without seeing the line it is hard to assess. I have delivered a few boats with bare dyneema/spectra line on the dinghy davits. Almost all had some abrasion. Enough that I added a separate line to take the load off the dyneema. Assuming yours showed no sign of abrasion, it would have to be UV related.

Dyneema has two enemies- chafe and UV. Bare dyneema is exposed to both!

I installed dyneema lifelines on my personal boat. My plan is to replace them every 4-5 years. Looking at the outside of a line is the normal way to inspect a cored line. If the jacket looks good, it is assumed the core is good. BUT when you place into duty what is often the core of the line as the jacket and the core, you loose the protection of a jacket.

At this point someone will tell me how they feel dyneema will last 10-15 years. Maybe on your boat. But where my life is concerned, I replace it early.

Further reading
Life cycle of dyneema https://www.riggingdoctor.com/life-a...les-of-dyneema
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Old 19-02-2020, 06:42   #10
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Re: 8mm spectra goes BANG. Sun degradation?

Generally it will get fairly fuzzy as the outer fibers breakdown well before failure at such low percentage of breaking. Could also be wasn't entirely Spectra as lots of "club race" line was made with only about 30% Spectra in the core
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Old 19-02-2020, 07:21   #11
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Re: 8mm spectra goes BANG. Sun degradation?

Article from Evans Starzinger that address last the topic. I suggest reading the article, very well done as usual from Evans.

The bottom line is that it is unlikely to be UV degradation considering it was very lightly loaded 8mm line. Something else happened to the line, or it was a manufacturing defect.

Worst case 5,000 kg breaking strength would be expected to retain 40% of its strength at -0 years of exposure, or 2,000kg. That’s a big dingy.

Quote:
UV resistance
HMPE is one of the most UV resistant fibers. The loss of strength depends on the line’s specific construction (diameter, braiding angle, type and amount of coatings) and the location (UV intensity). The line strength drops relatively rapidly during the first 18 or so months and then much more slowly after the surface of the fibers has been ‘burned’. As shown in the graph below (two different tests conducted in two different locations with two different lines, but both 8mm dia) they will lose about 20- 35 percent of their tensile strength (leaving 65-80 percent of the original tensile strength) within 24 months of continuous sun exposure and at five years will retain about 50-75% of its tensile strength, and 40-70% at 10 years. It should be noted that that there is some very tentative test results that suggest that double braid covers allow a significant amount of UV thru to damage the core, and so double braid line does not eliminate this UV aging problem.
https://www.ussailing.org/wp-content...n-Jan-2014.pdf
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Old 19-02-2020, 07:38   #12
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Re: 8mm spectra goes BANG. Sun degradation?

In 2004 we installed double braided lifelines of someItalian brand, with a polyester cover and a Dyneema/polyester blend core. After taking out initial stretch over the first week or so, the lines stayed tight for 8 years, then began to stretch again. This is where we replaced them.

Also in 2004 we installed Samsom Amsteel Blue 3/8Ē running backstays and we still have them. The outside looks faded from UV exposure, but when you shift fibers a bit, you see the original color right underneath the outer fibers. They are still fine, when we set a runner, it is still as tight many hours later. Iím sure it lost part of itís strength, but not enough to make it a top priority to replace it and this shows that the larger the diameter, the better UV resistant it gets, just like with polyester sewing thread for canvas
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Old 19-02-2020, 10:17   #13
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Re: 8mm spectra goes BANG. Sun degradation?

Almost no way to determine if the line was point overloaded in it's previous life.
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Old 19-02-2020, 10:23   #14
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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

Environment damage , mostly UV , reduces the strength of spectra about 10 percent per year

Spectra is also negatively affected by torque loading
6 twists per meter is the danger zone
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Old 19-02-2020, 11:13   #15
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Re: 8mm spectra goes BANG. Sun degradation?

slug said: "Environment damage , mostly UV , reduces the strength of spectra about 10 percent per year "


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


UHMWPE is very sensitive to heat, however - if the spot that failed had been heated over 200 degrees at some point, extensive damage may have occurred. With 15-year old line, you might never know. Also, the core of double-braid is unlikely to have UV protection in it, as it would be expecting the sheath to handle that.


BTW, while Dyneema/Spectra/Amsteel is available in colors, the only base colors are white and (rare) black - everything else is coloring applied to the outside (which will fade).



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