Another dyneema line failure

[Paul L]

Originally Posted by jfranta

For Dyneema line, there mare many different variations of Dyneema Chemistry sk60, sk75, sk78, sk90, sk99, DM20, etc., then there are many different variations of braiding geometry, last there are many different types of urethane coatings for UV resistance. When we first started using Dyneema for standing rigging at Colligo Marine, 12 years ago, I struggled with the number of variables. We went with the most reliable chemistry, SK75, from the highest volume and longest lasting supplier (and Heat stretcher) of line, Hampidjan. SK75 is still the best for standing rigging because it heat sets better than even the newer chemistries. We developed very conservative processes in splicing and handling because of the unknowns with this new technology to cover out butts for all these variables. We use very conservative bending ratios and splicing mechanicals like a 72 times bury and, always a Brummel splice that will never shake out. We developed very conservative hardware to use with the line. The compression strength difference from the tensile strength even presents some challenges but we overcame them along with the issues with thermal expansion. We understood creep early on and how to design around it successfully. We did some early UV testing and have an ongoing UV study in real time product usage on boats from all over the world. Suffice it to say, Dyneema is like Steel, there are many chemistries and physical differences in them. Choosing the right product and using it the right way is essential. As of today, we have provided standing rigging on over 900 boats, around the world, all major types of rigs to 100 feet waterline, with no Dyneema failures. We have even done a few B&R rigs now!

Long term UV life prediction data from sailboats can be found here: https://syntheticstandingrigging.com/

We say, conservatively, 5-8 years in the tropics for UV life. Very conservatively, like the rest of our design work.

It's physics, there are rules but you also have to design for the unknowns.

If anyone needs help sizing it just send an email. We can't predict the life of other's products but we can, at least, help size for equivalent stretch.


John Franta, Colligo Marine.

John,
No doubt there are many good examples of reliable dyneema based rigs around.
The part that throws me on this break is its location. It is not near the bend where it goes through the large block. It is not near where it passes through the bimini. It is about half way between the bimini and the block. The most notable part of that location is that it is running parallel to a smooth pvc 3/4 - 1 in pipe.

I always thought that UV deterioration on dyneema line occurred primarily on the surface. Since it is sized to be significantly over any expected breaking load, I would not expect that to cause the break. I pulled this line out about 7 months ago for inspection. It had some obvious color change, but was not damaged.

I'm getting ready to head off on a 5,000 m passage and have lost a little confidence in the dyneema. Replacing with wire as we speak.

[Paul L]

A little more forensics info. I went over the line with the local rigger here. Looking at the line he believes it is the coated, heat treated dyneema. By pulling on portions of the core threads by hand at the break it is fairly clear that those threads have been severely weakened, most likely by UV. You can grab a chunk of threads and pull them out of the core. This is 4 year old line. At least the last 2.5 years has been in brutal UV conditions, Australia to SE Asia.

As I mentioned above, I was always under the impression that UV damage to dyneema was primarily on the outside layer and that core retained enough to easily stay in service. Perhaps not

[40 South]

Originally Posted by Paul L

A little more forensics info. I went over the line with the local rigger here. Looking at the line he believes it is the coated, heat treated dyneema. By pulling on portions of the core threads by hand at the break it is fairly clear that those threads have been severely weakened, most likely by UV. You can grab a chunk of threads and pull them out of the core. This is 4 year old line. At least the last 2.5 years has been in brutal UV conditions, Australia to SE Asia.

As I mentioned above, I was always under the impression that UV damage to dyneema was primarily on the outside layer and that core retained enough to easily stay in service. Perhaps not

Single braid dyneema does not have a core! It is made up of 12 sets of fibres plaited together.

Heat set dyneema (Dynice Dux etc.) does not like being load cycled as used in your application, it is more suited to standing rigging. It is stiff and hard. ''Regular'' SK75 is better for your application. You need to size for loads not diameter. If you keep the load <10% of the breaking strain you will get minimal elongation.

I suspect the strands have been internally chafing on each other. They are quite hard compared to ''regular'' dyneema.

I second John Franta's view on grade and manufacturer of the dyneema. You pay for what you get!

[Paul L]

Originally Posted by 40 South

Single braid dyneema does not have a core! It is made up of 12 sets of fibres plaited together.

Heat set dyneema (Dynice Dux etc.) does not like being load cycled as used in your application, it is more suited to standing rigging. It is stiff and hard. ''Regular'' SK75 is better for your application. You need to size for loads not diameter. If you keep the load <10% of the breaking strain you will get minimal elongation.

I suspect the strands have been internally chafing on each other. They are quite hard compared to ''regular'' dyneema.

I second John Franta's view on grade and manufacturer of the dyneema. You pay for what you get!

I was using the term core to mean the inner strands, not to mean a cored rope with an outer cover.

Given the size of the dyneema, I'm not convinced it is a very high load.
The line is attached to a hydraulic backstay adjuster. In reality this gets set and left, as we are a cruising boat. So I don't see this as significantly different than a fixed stay.

I have never heard of internal chafing on dyneema. Is this a common problem?
Not positive, but I think this was Donaghys line.

[40 South]

Originally Posted by Paul L

I was using the term core to mean the inner strands, not to mean a cored rope with an outer cover.

Given the size of the dyneema, I'm not convinced it is a very high load.
The line is attached to a hydraulic backstay adjuster. In reality this gets set and left, as we are a cruising boat. So I don't see this as significantly different than a fixed stay.

I have never heard of internal chafing on dyneema. Is this a common problem?
Not positive, but I think this was Donaghys line.

Hydraulic rams can output significant loads and they are unforgiving. I don't know the sizing of the ram or working pressure so cannot comment on actual loads.

Just about any rope/line will have a degree of internal chafe. Where the dyneema goes over the pulley it will distort the dyneema loading the threads unevenly. This can be transmitted further down the rope, pulling some shorter than others. This can lead to internal chafe. You may only be loading 75% of the rope with the other 25% under compression around the pulley. The loaded threads will ''see'' higher numbers, which may shorten the life of the line. A more flexible and soft rope would be better.

[Paul L]

Originally Posted by 40 South

Hydraulic rams can output significant loads and they are unforgiving. I don't know the sizing of the ram or working pressure so cannot comment on actual loads.

Just about any rope/line will have a degree of internal chafe. Where the dyneema goes over the pulley it will distort the dyneema loading the threads unevenly. This can be transmitted further down the rope, pulling some shorter than others. This can lead to internal chafe. You may only be loading 75% of the rope with the other 25% under compression around the pulley. The loaded threads will ''see'' higher numbers, which may shorten the life of the line. A more flexible and soft rope would be better.

So you aren't buying the UV as a significant cause? The break is probably 2 or 3 feet below the block. The block is a 5in Harken and I guess the line is on about 140-160degs or so, as the base is fairly wide at the chainplates.

[40 South]

Originally Posted by Paul L

So you aren't buying the UV as a significant cause? The break is probably 2 or 3 feet below the block. The block is a 5in Harken and I guess the line is on about 140-160degs or so, as the base is fairly wide at the chainplates.

If as you say the internal strands are the significantly damaged ones and from what I can see of the outer strands....no, I don't accept that UV is the issue here. I think it is uneven loading of the strands leading to internal chafe.

The large diameter block you are using will go some way to mitigating the uneven loads, but on any turn/radius there will be disproportionate loading of the strands. Dux (heat treated dyneema) does not like this type of application. When spliced onto thimbles the loads are basically static and will be ''worked'' out as the line is tensioned and the strands move into a more ''balanced'' position.

In relation to the loads you are applying....you have a 2:1 purchase on your backstay which has to counter the forestay loads to keep the mast vertical. What do you have for a forestay 10mm S/S?

Think about it....if the issue was UV then the outer strands of the dyneema would have the most significant damage before the inner strands became affected.

I have seen 50mm, 8 plait polyethylene chafe internally from being used to moor boats. The outer was fine except for normal wear & tear. It is caused by the disproportionate loading the rope strands which ''move'' across each other under cyclic loads.

I have also seen loaded dyneema cut into concrete! and groove steel bollards!

I have Dynice Dux standing rigging on my boat. It has been there for 6 years and looks as good as the day I spliced & fitted it. I also have dyneema lifelines and halyards.

[Paul L]

Originally Posted by 40 South

If as you say the internal strands are the significantly damaged ones and from what I can see of the outer strands....no, I don't accept that UV is the issue here. I think it is uneven loading of the strands leading to internal chafe.

The large diameter block you are using will go some way to mitigating the uneven loads, but on any turn/radius there will be disproportionate loading of the strands. Dux (heat treated dyneema) does not like this type of application. When spliced onto thimbles the loads are basically static and will be ''worked'' out as the line is tensioned and the strands move into a more ''balanced'' position.

In relation to the loads you are applying....you have a 2:1 purchase on your backstay which has to counter the forestay loads to keep the mast vertical. What do you have for a forestay 10mm S/S?

Think about it....if the issue was UV then the outer strands of the dyneema would have the most significant damage before the inner strands became affected.

I have seen 50mm, 8 plait polyethylene chafe internally from being used to moor boats. The outer was fine except for normal wear & tear. It is caused by the disproportionate loading the rope strands which ''move'' across each other under cyclic loads.

I have also seen loaded dyneema cut into concrete! and groove steel bollards!

I have Dynice Dux standing rigging on my boat. It has been there for 6 years and looks as good as the day I spliced & fitted it. I also have dyneema lifelines and halyards.

The forestay is 11mm and solent is 10mm.

I just looked up the quote/bill. The dyneema is labeled as 8mm dynex. I just put a caliper on the smallest part and it came out 9mm. The rest of it must be bunched up as it measures larger (not at the splices). So it isn't as large a diameter as I thought.

[40 South]

Originally Posted by Paul L

The forestay is 11mm and solent is 10mm.

I just looked up the quote/bill. The dyneema is labeled as 8mm dynex. I just put a caliper on the smallest part and it came out 9mm. The rest of it must be bunched up as it measures larger (not at the splices). So it isn't as large a diameter as I thought.

From the info I have Dynex Dux doesn't come in 8mm, 7mm or 9mm. It is made from larger sizes and stretched so it finishes smaller.

OK, a few numbers for you to think about.......9mm breaking strain = 10900kg, 7mm = 7500kg, (from info I have) therefore working on a 20% safety margin, working loads should be below 2180kg load for 9mm and 1500kg for 7mm. You might want to check the capacity of the ram. It is running 2:1 so only needs 5450kg to break 9mm! I think it will be higher than these numbers. You have 2 headstays to ''work'' against, a combined capacity in the order of 17200kg, so there will be no give no matter how hard you work the ram. The weak link is the dyneema.

[Paul L]

Originally Posted by 40 South

From the info I have Dynex Dux doesn't come in 8mm, 7mm or 9mm. It is made from larger sizes and stretched so it finishes smaller.

OK, a few numbers for you to think about.......9mm breaking strain = 10900kg, 7mm = 7500kg, (from info I have) therefore working on a 20% safety margin, working loads should be below 2180kg load for 9mm and 1500kg for 7mm. You might want to check the capacity of the ram. It is running 2:1 so only needs 5450kg to break 9mm! I think it will be higher than these numbers. You have 2 headstays to ''work'' against, a combined capacity in the order of 17200kg, so there will be no give no matter how hard you work the ram. The weak link is the dyneema.

Gotta include the 11mm 1x19 backstay in those calculations. That ought to be about a 10,000kg breaking. So it matches the halved dynex fairly well.

[40 South]

Originally Posted by Paul L

Gotta include the 11mm 1x19 backstay in those calculations. That ought to be about a 10,000kg breaking. So it matches the halved dynex fairly well.

Your 10mm backstay should be around 8600kg BS. It may be higher depending on the grade and manufacturer. The ram has the power on the 2:1. As I said earlier it only needs 5450 kg force to break the dyneema which will be stressed by the bending over the block.

Anyhow, you are/have replaced with wire.

Good luck with the wire, hope it holds up.

[jfranta]

Originally Posted by Snore

I have no data. What is really needed is 'someone' to do scientific testing.



Your anecdotal data, may support my theory. When you have seen the internal damage, what did you do? Reduce tension?


Don't misunderstand me- I am a fan of dyneema. I have it for my topping lift and lifelines on my boat. I also use it to make custom jacklines for each delivery (use once or twice and throw away). Great stuff, these frequent failures are troubling

It was not our rigging but Heat stretched Dyneema from another supplier. It was undersized and increasing the size for the stretch that was needed solved the issue. John Franta, Colligo Marine.

[jfranta]

Originally Posted by Paul L

Gotta include the 11mm 1x19 backstay in those calculations. That ought to be about a 10,000kg breaking. So it matches the halved dynex fairly well.

If your backstay is 11 mm 1 x 19 we would use 13 mm Dynice Dux for it. This is equivalent stretch to the 11mm 1 x 19. It also gives you, 79200 kgs of breaking strength. After 10 years in tropics you will still have 31680 kgs of break strength left, per our data. Your backstay was too small for elasticity and did not give you enough of a factor of safety. Please use the equivalent stretch numbers on our site. Dyneema is a new material and its limiting parameter for standing rigging is Elastic Stretch. 9 mm dyneema is equivalent stretch to 1/4" 1x19 so your backstay was too stretchy, this meant you did not have the UV life AND you did not have the fatique life. Size it for stretch, then creep, and your strength will always be 2-5 times stronger than you need. There are creep tables on our site also.

John Franta, Colligo Marine

[jfranta]

Originally Posted by Paul L

John,
No doubt there are many good examples of reliable dyneema based rigs around.
The part that throws me on this break is its location. It is not near the bend where it goes through the large block. It is not near where it passes through the bimini. It is about half way between the bimini and the block. The most notable part of that location is that it is running parallel to a smooth pvc 3/4 - 1 in pipe.

I always thought that UV deterioration on dyneema line occurred primarily on the surface. Since it is sized to be significantly over any expected breaking load, I would not expect that to cause the break. I pulled this line out about 7 months ago for inspection. It had some obvious color change, but was not damaged.

I'm getting ready to head off on a 5,000 m passage and have lost a little confidence in the dyneema. Replacing with wire as we speak.

Most of the pull testing we have done for our longevity testing the line breaks in the middle away from splicing. If the splicing was done correctly. Based on your other posts this is UV damage and the line was sized too small. ALWAYS size for equivalent Stretch and you will have the performance and the life that you want! New material=new rules.

John Franta, Colligo Marine.

[thinwater]

Originally Posted by Snore

... I am fairly confident it is chafe. But.... It is internal chafe as the result of the line developing a harmonic vibration.

To be clear, we have all heard the standing rigging howl in a 25+ knot wind. That howl is the shrouds vibrating in the wind. I am very confident that when dyneema vibrates, it chafes internally....

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.