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Old 02-19-2020, 12:40 AM   #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 02-19-2020, 12:59 AM   #2
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How was it terminated? Did it break at a knot? In any of the low stretch line filaments, any knot will reduce the strength by 60-70%, and an unfortunately chosen knot by 80% or more. Spectra is fairly UV resistant compared to some of the others like liquid crystal or PBO.
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Old 02-19-2020, 01:21 AM   #3
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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 02-19-2020, 01:56 AM   #4
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Given that you removed the original cover it is possible that what you had was never intended to be exposed to UV.

I've been using some uncovered Spectra (or equivalent, not sure of brand) for the same purpose for 8 years without issues. But the stuff I have was designed/supplied without any covering. Maybe it has some kind of chemical UV treatment, I don't really know.
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Old 02-19-2020, 03:49 AM   #5
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Maybe, though we used to strip outer cases off to save weight just leaving the case where it went around winches or through jammers and never had issue and with actual real load, not a mere 300kg.

Also I would have though the outside fibres may break down but the inside would not be seeing sun so should be unaffected.
Seems odd.
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Old 02-19-2020, 06:21 AM   #6
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Is there any chance that the profile of the channel in the pulleys is V shaped rather than U shaped? A friend ran into this problem when he converted the line on an older davit from wire rope to Spectra. The original pulleys were V shaped which I gather is common for wire rope. He ended up having the chance the pulleys for U shaped channels to stop the Spectra from breaking.
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Old 02-19-2020, 06:41 AM   #7
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Nope, u shaped stainless steel sheaves.
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Old 02-19-2020, 05:56 PM   #8
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From the yachtie forum.......

Quote:
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.


https://www.cruisersforum.com/forums...ml#post3077941
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Old 02-19-2020, 06:57 PM   #9
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Quote:
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Given that you removed the original cover it is possible that what you had was never intended to be exposed to UV....

This sounds plausible and worth further investigation on your part.
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Old 02-19-2020, 08:02 PM   #10
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My understanding is that Spectra does very well in terms of UV resistance and can be used uncovered. I've got lots of uncovered dyneema on my sailboat and have researched it quite carefully.

But still, you're in a very high UV zone, right? Maybe they were used a bit longer than two years on your sailboat? 5 years of constant exposure may be a realistic maximum duty cycle in your use. Just speculating here, but it's a harsh environment.

The other risk to this material is temperature. Friction can kill it. Melting temp is something like 150C. Did you have it on a capstain or anything like that?
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Old 02-19-2020, 08:07 PM   #11
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Nope, u shaped stainless steel sheaves.
What diameter are the sheaves? If its fairly small then bending & friction between fibres could be high.
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Old 02-19-2020, 08:31 PM   #12
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May be comparing apples to oranges, but I found a climbing rope study which determined that a ropes sheath contributed 19% to the ropes strength.
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Old 02-19-2020, 08:31 PM   #13
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I have no idea of what the minimum radius is for the line you used but if the sheaves are too small then the bends can damage the line. Add that to possible UV damage and any line can be substantially weakened.

Age can cause damage and it may not be predictable. Ozone, garage chemicals, and so on .
I realize you may know this but?
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Old 02-19-2020, 08:51 PM   #14
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What diameter are the sheaves? If its fairly small then bending & friction between fibres could be high.
50mm/2inch
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Old 02-19-2020, 08:56 PM   #15
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Quote:
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My understanding is that Spectra does very well in terms of UV resistance and can be used uncovered. I've got lots of uncovered dyneema on my sailboat and have researched it quite carefully.

But still, you're in a very high UV zone, right? Maybe they were used a bit longer than two years on your sailboat? 5 years of constant exposure may be a realistic maximum duty cycle in your use. Just speculating here, but it's a harsh environment.

The other risk to this material is temperature. Friction can kill it. Melting temp is something like 150C. Did you have it on a capstain or anything like that?

2 years on a sailboat with outer case on.
Removed and went up a size when we put a large square topped main on.
That rope then sat in shed until I got it out a few years ago and stripped the outer case off to re purpose it for the davits.

The winch it is used on is a 3 speed hand cranked trailer winch, so no slippage.
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Old 02-19-2020, 11:31 PM   #16
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Overloading? Overloading a line even once can greatly diminish it's capacity. Never trust a line after it has been overloaded.
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Old 02-20-2020, 01:56 PM   #17
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Doubt it had more than 50% load as a halyard and 10% as a dingy davit rope.
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Old 03-06-2020, 01:43 PM   #18
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You mention a locked Brummel, but did it have a proper tapered, buried tail, 72 x diameter (8mm) is about 23"? The Brummerl keeps the bury from shifting under low loads only.
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Old 03-06-2020, 05:10 PM   #19
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Quote:
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Given that you removed the original cover it is possible that what you had was never intended to be exposed to UV.

I've been using some uncovered Spectra (or equivalent, not sure of brand) for the same purpose for 8 years without issues. But the stuff I have was designed/supplied without any covering. Maybe it has some kind of chemical UV treatment, I don't really know.
I used spectra for the dinghy crane and made up a simple velcro sleeve to wrap around the constantly exposed portion of the rope. The rest of the rope is only ever exposed for 10 minutes or so when launching or retrieving. I only had this in place for a few years before selling the boat but I think it gives you complete confidence in avoiding UV deterioration at a nominal cost.
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