Another dyneema line failure

[Paul L]

There was a post a while back about a dyneema topping lift that parted mid way. Don't think there was much of a conclusion on what actually caused it.
https://www.cruisersforum.com/forums...re-240423.html

Our backstay is rigged as a single, long wire that runs to a large block. Then a split back stay runs from a port chain plate through the block and back down to a starboard side Navtec hydraulic backstay adjuster. When I redid the standing rigging a few years ago I was not able to source the 7x19 stainless wire for the lower portion. In its place I rigged 7/16in dyneema.

Before Covid season started I took the dyneema off and inspected it. It appeared fine. Fast forward 7 months. The boat has been on the hard stand under the SE Asian sun. When I return I see the dyneema backstay has parted. The Navtec had a little oil on the top rod, so I suspect that it slacked partially. It was hard retracted, so I don't believe it became fully loose.
The dyneema goes from the Navtect through the bimini and up to the block, maybe 10-12 ft up. There is a smooth, PVC pipe that runs next to it that holds the SSB antenna wire.
The break in the dyneema occurred about 2-3ft above the bimini. There is nothing there except the PVC pipe.

Can't see why it chafed through.

[Chotu]

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

[Biggfell]

What make and spec was your Dyneema Paul?

[Hardhead]

It looks like it's chafed quite a bit above and below the break - is that right? Seems kinda weird...

[Paul L]

Originally Posted by Hardhead

It looks like it's chafed quite a bit above and below the break - is that right? Seems kinda weird...

It does look that there is some roughness beyond the break. The strange part is that the break is far above the bimini and below the upper block. So I am at a loss to see what it chafed on, except the smooth PVC pipe.

It is being replaced with wire as we speak.

[ggray]

Many of us are hoping to replace wire with dyneema, so thanks for the information!

I assume that the original wire was smaller than the 7/16 dyneema? What brand "dyneema" is it?

[s/v Jedi]

Not answering the questions on which brand it is tells the story: same as previous cases. For such critical components, only the best is suited.

I’m pretty convinced this is not Samson, New England Ropes, Marlow etc.

[jfranta]

Originally Posted by Paul L

It does look that there is some roughness beyond the break. The strange part is that the break is far above the bimini and below the upper block. So I am at a loss to see what it chafed on, except the smooth PVC pipe.

It is being replaced with wire as we speak.

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.

[Benz]

I do a lot of work in a rigging shop, and have never seen a failure due to UV alone. The failure mode is almost always chafe.

[Snore]

Originally Posted by Benz

I do a lot of work in a rigging shop, and have never seen a failure due to UV alone. The failure mode is almost always chafe.

Looking at the failure of my topping lift and the failure of other long dyneema lines, 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. That internal chafe causes threads to fail, then strands and finally catastrophic failure.

Hmmmm sounds like a job for Practical Sailor!

[jfranta]

Originally Posted by Snore

Looking at the failure of my topping lift and the failure of other long dyneema lines, 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. That internal chafe causes threads to fail, then strands and finally catastrophic failure.

Hmmmm sounds like a job for Practical Sailor!

Any supporting data? We know of internal damage in a dynamic sheave system with high loaded shrouds that were undersized so too much elasticity but never any internal damage from harmonics in standing rigging. When we see harmonic issues we just have the customer change the tension slightly. Not sure if harmonics would show movement between the strands anyway. This might happen with non-heat stretched dyneema? In over 900 boats for 12 years now with our rigging, heat stretched SK75 from Hampidjan we have never seen what you are suggesting.

John Franta, Colligo Marine

[Boatguy30]

The part on the cockpit floor is very fuzzy. Sure sign of UV damage.

I’ve seen plenty of dyneema fail due to UV exposure alone. Have never heard of or seen this “internal chafe” it’s all external from UV or actual other external chafe. Had a 5 y/o Amsteel outhaul fail on my boat a few months ago. Right at the aft end of the stackpack. And it wasn’t even fuzzy!

[Snore]

Originally Posted by jfranta

Any supporting data? ....

John Franta, Colligo Marine

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

Originally Posted by jfranta

We know of internal damage in a dynamic sheave system with high loaded shrouds that were undersized so too much elasticity but never any internal damage from harmonics in standing rigging. When we see harmonic issues we just have the customer change the tension slightly.

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

[Orion Jim]

I use 3/16” Amsteel blue for my topping lift. When I catch the sun just right I notice it’s beginning to look a bit hairy after five or six years so I replace it. This equates to sun exposure for seven months a year with a passage from New England to Bermuda seasonally and a couple months spent in Bermuda exclusively. I’ve never had a failure but my aim is to be proactive and never experience one.

[Paul L]

Originally Posted by ggray

Many of us are hoping to replace wire with dyneema, so thanks for the information!

I assume that the original wire was smaller than the 7/16 dyneema? What brand "dyneema" is it?

The original wire was 3/8in 7 x 19. The rigging was done by a rigger in New Zealand, so I suspect the line was Australian. It is approx 4 years old.