Another dyneema line failure

[Snore]

Originally Posted by thinwater

Why are you "very confident?" To my understanding (which could be wrong) Dyneema line has a track record running around pulleys both on boats and in logging applications suggesting better flex life and resistance to internal chafe than any other material. Stainless steel, on the other hand, is not impressive when flexed, though because it is heavier it would have a different harmonic period. Also, the amount of flex when oscillating in the wind at that distance from the end would be very slight.



I'm not sayin' this could not be the case. But a statement like that needs to be more than a feeling, since most of what we know does not point that way.

As you may recall, there have been a few failures when people failed to taper their splice. The “shoulder” formed at the buried end caused chafe that resulted in failure of the line at the splice.

So we have proof that it can happen.

We have had several failures of long runs of dyneema. Yet, oddly, there are no records of shrouds failing. So the cause of the failure is unclear. The fact that at least two happened towards the middle of the run sort of led me to my assumption.

Once again this was not cheapo off-brand line. It was purchased in West Marine

[Benz]

Originally Posted by Snore

As you may recall, there have been a few failures when people failed to taper their splice. The “shoulder” formed at the buried end caused chafe that resulted in failure of the line at the splice.

So we have proof that it can happen.

We have had several failures of long runs of dyneema. Yet, oddly, there are no records of shrouds failing. So the cause of the failure is unclear. The fact that at least two happened towards the middle of the run sort of led me to my assumption.

Once again this was not cheapo off-brand line. It was purchased in West Marine

The failure of un-tapered splices is not from chafe, I thought, but because it creates a stress riser that greatly weakens the line. Any line will suffer similarly from stress risers, but I understood Dyneema to suffer the most.

[Snore]

Originally Posted by Benz

The failure of un-tapered splices is not from chafe, I thought, but because it creates a stress riser that greatly weakens the line. Any line will suffer similarly from stress risers, but I understood Dyneema to suffer the most.

I believe there is some ambiguity in your statement.

What forces cause the outer/host line to fail? Logically, the stress riser either caused chafe or heat, weakening the line and making it more susceptible to chafe.

Am I missing something??

Is there another force at work?

[Benz]

Originally Posted by Snore

I believe there is some ambiguity in your statement.

What forces cause the outer/host line to fail? Logically, the stress riser either caused chafe or heat, weakening the line and making it more susceptible to chafe.

Am I missing something??

Is there another force at work?

These are deeper waters than I can sound, not being an engineer, but chafe seems counterintuitive since there's no sawing motion. I thought it was that a sharp bend causes weakness because the force increases dramatically at a dogleg. Again, not an engineer, so this is my gut.

[Snore]

Originally Posted by Benz

These are deeper waters than I can sound, not being an engineer, but chafe seems counterintuitive since there's no sawing motion. I thought it was that a sharp bend causes weakness because the force increases dramatically at a dogleg. Again, not an engineer, so this is my gut.

Agreed. This is over my head also. Really need an engineer to weigh in.

[seacap]

I have had Dyneema on my boat for 11 years here in the deep tropics and have been putting on hard sailing miles down to Trinidad and back up to Puerto Rico. I am now using black Dyneema for even better UV protection. No problems yet. Have always used name brand Dyneema. New England Ropes and Samson.

[john manning]

I have seen similar breaks in synthetic rope caused by the rope fluttering in wind and hitting an adjacent object.

[sails4fun]

With manufacturers selling products that are called "Dyneema" from Asia that are not Dyneema (which is the trade name of the product manufactured by DSM), the quality of fiber ranges all over the scales. Best to keep to brand name manufacturers, They design their products using engineering of fiber choice, braid angle design and coating choices. All are important in the final product! My experience is that HMPE fibers degrade in UV. The outer fibers degrade faster than the interior fibers. HMPE fibers generally are pretty good in UV when compared with other fiber used in high tensile ropes. Failure of line is due to chafe most often. When a line fails due to excessive loading, the ends appear as if melted when examined under magnification. This is due to the heat build up when the fiber is elongated beyond the tensile strength. I have not seen any case of high tensile rope failure due to the failure of inner strands of the load carrying braid.

[Kim Klaka]

Originally Posted by Chotu

Yup. I’ve had the same experience with dyneema breaking under load repeatedly without chafe.

I had a dyneema backstay break about 5 years go (in the pen, luckily). Can't remember the make of rope, but it was professionally made up by our local rigger who supplies a lot of the offshore racing yachts. UV degradation did not explain it, as it was significantly over sized. (If UV had been the cause, almost all rope rigging here would fail quickly, but it doesn't) I think I posted the details of the incident on this or a similar forum, no clear explanation was offered by the many contributors. I even discussed it with the late Brian Toss in a Skype call, again he could not come up with a satisfactory explanation. I reverted to stainless steel.

The only explanation that made sense was given by the french ocean racing legend Philippe Peche (Jules Verne winner) , who suggested parrots had been pecking at the rope. I found this difficult to believe until a year later I saw 3 parrots perched on the backstay of a nearby boat, happily pecking away (they were having a hard time of it as this backstay was stainless steel). Cockatoo parrots here in Australia have been known to peck wooden structures (pergolas etc.) to bits in very quick time, so their destructive capacity is well known. Maybe you have similar strong-beaked birds where you are? Ours seem to prefer angled perches, not vertical ones, so shrouds are perhaps less vulnerable. Any sailing ornithologists out there who could enlighten us?

[pbmaise]

I used Donaghy's jacketed Dyneema on my rigging and replaced after about 8 years of service. I found the lines to be very stiff and I took this to be owing to UV damage despite the jacket.

In this case four years and no jacketing may be the reason for failure.

One key point mentioned by the rigger here is turning radius. I made the mistake of first launching using conventional stainless thimbles sized for the line size and found they were soon crushed like a tin can. People recommend I have a reinforcement welded into the thimbles. These didn't crush but cut into the line and I found damage owing to the right radius .

I finally switched to very large heavy and heavily galvanized thimbles.

I am curious about how Paul keeps describing a parallel PVC pipe. He says it is smooth, however ends of a pipe are sharp. Also could a parallel pipe been banging against the rope repeatedly causing heat.

Further, Paul described the line as being heat treated. Perhaps this heat treatment was excessive in that area.

[Benz]

^^The stiffness is not necessarily UV damage, but simply a by-product of having a rope set up under tension for a long time. Dust and salt get into the cover and stiffen it up, and it simply gets "set in its ways." Consider that when you first unroll a new bit of rope off the spool, it retains the stiffness and memory of being tightly rolled until it's used in other ways for a while.
Heat-set rope when brand new is also pretty stiff--again not due to damage but to being pulled hard and compacted at the factory.

[Paul L]

Originally Posted by pbmaise

I used Donaghy's jacketed Dyneema on my rigging and replaced after about 8 years of service. I found the lines to be very stiff and I took this to be owing to UV damage despite the jacket.

In this case four years and no jacketing may be the reason for failure.

One key point mentioned by the rigger here is turning radius. I made the mistake of first launching using conventional stainless thimbles sized for the line size and found they were soon crushed like a tin can. People recommend I have a reinforcement welded into the thimbles. These didn't crush but cut into the line and I found damage owing to the right radius .

I finally switched to very large heavy and heavily galvanized thimbles.

I am curious about how Paul keeps describing a parallel PVC pipe. He says it is smooth, however ends of a pipe are sharp. Also could a parallel pipe been banging against the rope repeatedly causing heat.

Further, Paul described the line as being heat treated. Perhaps this heat treatment was excessive in that area.

The PVC pipe was lead parallel to the dyneema to hold my HF antenna wire. The ends of the pipe were beyond the dyneema and the pipes hold downs were also beyond the dyneema.

The heat treated comment came from a rigger that looked at the break. The original purchase order calls out Dynex, which I assume is dynex dux.

[Linwood4]

A quick thought. For others that are looking for why these lines fail. Id also have a look at highly reflective objects on your deck and on boats near yours. I have seen flexible solar cells creating a parabolic mirror effect and cause some chaos. Im not suggesting this is why these are failing but it might help someone...

[Breaking Waves]

Originally Posted by Snore

Logically, the stress riser either caused chafe or heat, weakening the line and making it more susceptible to chafe.

Am I missing something??

Is there another force at work?

yea, you are missing the whole concept of a 'stress riser'. In an undisturbed straight section of the line, all the filaments will be carrying an equal load. If you disturb that line/braid, by for example changing direction or distorting the braid, then some filaments will start to carry more load and others less load. Those filaments carrying more load will now break sooner at a lower total loading on the line. That differential loading is the 'stress riser'. I (and many others) have tested this extensively. It is established fact. Just for reference - a 1:1 bend will weaken the strength by (approximately) 50%, an untapered splice bury will weaken it by (approximately 20%) and a Brummel will weaken it by (approximately) 10%.
Stress risers happen in sharp corners and holes in solid metal also just for example - there is no 'chafe' necessary/involved in the effect.

Originally Posted by Paul L

I always thought that UV deterioration on dyneema line occurred primarily on the surface.

In a (typical) single braid, ALL the filaments come to the surface quite regularly. The whole line is cooked. There are no 'protected' filiments. You have to assume a (roughly) 50% strength reduction after (about) 24 months of exposure (it might be less depending, but 50% is the safe assumption).

Even putting a braided cover over the line does not provide much UV protection (it does offer some chafe protection). Testing shows that the core in a (recreational sized) double braided line still takes around a 50% strength hit from UV. Samson testing indicated you needed a 4mm thick cover (so 8mm of 'extra' cover diameter) with a very tight weave to start providing UV protection to the core.

The 'pro engineering' way to provide UV protection is either with solid rubber (like heat shrink tubing) or solid plastic (various dip/bath options). If you look at how the really top rigging companies (like Southern Spars) provide textile stays you will see that they are covered in this way. like this:

'Singing' causes fatigue, which is a whole different mechanism that weakens the line.

[Paul L]

Originally Posted by Breaking Waves

.....


In a (typical) single braid, ALL the filaments come to the surface quite regularly. The whole line is cooked. There are no 'protected' filiments. You have to assume a (roughly) 50% strength reduction after (about) 24 months of exposure (it might be less depending, but 50% is the safe assumption).

Even putting a braided cover over the line does not provide much UV protection (it does offer some chafe protection). Testing shows that the core in a (recreational sized) double braided line still takes around a 50% strength hit from UV. Samson testing indicated you needed a 4mm thick cover (so 8mm of 'extra' cover diameter) with a very tight weave to start providing UV protection to the core.

The 'pro engineering' way to provide UV protection is either with solid rubber (like heat shrink tubing) or solid plastic (various dip/bath options). If you look at how the really top rigging companies (like Southern Spars) provide textile stays you will see that they are covered in this way. like this:

'Singing' causes fatigue, which is a whole different mechanism that weakens the line.

Those UV numbers are pretty brutal if they are accurate. Surprising that a standard braid cover does little to help.


Interesting comment on 'singing'. We replaced the adjustable dyneema portion of the backstay with fixed, wire. Just completed a 10 day passage in the Indian Ocean. When we were out there one morning my wife said to me, 'Have you noticed the humming is gone from our rig?'