Issues with synthetic rigging?

[Kim Klaka]

Great forum! Thanks indeed for your further thoughts Brion, and for putting the issue in perspective for the general reader. I still think there is something unexplained going on, and would appreciate further ideas from yourself and others.
So as I understand it for the general reader we have to note that:
1.
Whilst variations in splicing technique will lead to fluctuations in breaking load, so do fluctuations in wire swage tolerances. And its probably a lot easier to tell if a splice has been done badly than it is to tell if a swage has been done badly. Advantage plastic rigging.
2.
Both plastic rigging and stainless wire degrade in the environment - plastic due to u-v and wire due to salt etc. (however, the degradation rate in wire increases as it gets older whereas the degradation rate in plastic is greatest in the first few years then levels off). U-V degradation of Dyneema implies a covering is advisable in extreme sunlight. No advantage to either plastic or steel, just different.

Then to the specific case of the broken spectra backstay:
The load in this case was not applied by the wind, it was applied by me pulling the backstay tackle on in the pen before we even put the sails up. This is just a standard cruiser-racer with a standard block and tackle. I have sailed on lots of boats that apply a very much higher pre-tension in their (wire) backstay. Without revisiting the sums, the bottom line is that the spectra broke when the backstay tackle was applied whereas the wire never broke under very much higher loads exerted by the exact same backstay tackle plus the much bigger loads of wind and waves. This despite the plastic rope having a higher quoted breaking load than the wire. Even when you consider all the factors (u-v –salt corrosion, splice quality, swage quality, creep-induced weakness etc.) it just doesn’t add up that a stronger plastic rope breaks at a hugely lower load than a weaker stainless wire.

There’s something missing in the analysis which needs a bit more investigating. Suggestions, anyone?
Kim

[Brion Toss]

Hi again,
According to one insurance company's claims for dismastings, most occur in low windspeeds. This has to do with characteristics of metal, especially work-hardening, plus wave action, plus most boats are in relatively low winds most of the time. It is not because low windspeeds inherently make things break.
Likewise it is safe to assume that your backstay didn't break because you pulled on the tackle under way. It is far more likely that it had been approaching breaking for quite some time, and when you put the load on it (an unknown load, I will add), your effort exceeded the rope's capacity to stay together.
And I disagree; I think that it does "add up" that a series of factors resulted in an ostensibly stronger rope breaking, when wire in similar circumstances didn't. It was rope not optimal for standing rigging, it had an at best utilitarian splice; it was sized far too small for the load, it had been living, unprotected, in very harsh sunlight, and, perhaps most importantly, we don't even know what the rope was, so we can't make any judgement relative to its original quality. Too many variables.
For one chart on the expected behavior of Spectra in UV, see file:///C:/Users/Brion/Documents/Rigging%20Information/Rope/US%20Sailing%20Spectra%20UV%20chart.htm. You can find the original document, which is about lifelines, here: http://www.ussailing.org/wp-content/...n%2020 14.pdf.
Fair leads,
Brion Toss

[Kim Klaka]

Hi,
Fascinating article by Evans on Spectra lifelines, thanks.
I think we are more or less agreed on the need to protect spectra from sunlight in extreme climates, and that quality control of splices requires comparable standards, and has similar implications, to the required QC on wire swages.
We shall just have to agree to disagree for now, about whether the load I applied to the backstay was excessive. Seeing as nobody else has posted on this thread recently I'll close. If I get the opportunity to take some load measurements I may revisit the discussion.
In the meantime thanks for a very enlightening and thought-provoking thread. As with most research, questions lead to more questions!
Kim

[keithasully]

I am interested in rerigging my sailboat and trying to decide what material to use. When I read all the comments about synthetics 25% strength loss due to UV, failure due to incorrect splices, increased cost, why use it? Standing rigging is pretty important. Why spend so much more for a rig that deteriorates so much so quickly?

[Stumble]

To start with synthetics typically start out around double the strength of steel wire in order to control creep. So you loose 25% of the strength and still have rigging that is 175% stronger than the wire it replaced.

[John Stone]

Stumble, true enough. But, for some it's not that simple. I have dyneema life lines--and I like them. I incorporates a dux forestay for my stays'l so I could gain some personal experience with dux. So far, it has held up well in the tropics for the past three months. I've had it on the boat for 9 months. All that time with bronze hanks for the stays'l. No complaints. I briefly considered going with dux for all my standing rigging while building the new mast for my 8 ton bermuda rigged cutter. I liked the whole idea, especially the ease of splicing and the lighter weight. But, as I recall I had to go with 5/8" turnbuckles as I needed 9mm dux when sized for creep. Have you priced them lately? Yow! The rig is too big for dead eyes. When I priced it all out the whole dux setup was nearly three times the cost of 7x7 316 SS that I spliced myself and that did not include the price of the bigger turnbuckles delux required. I expect to see very little work hardening in the standing rigging with Liverpool splices around bronze thimbles. I think I should be able to get 10 good years out of the 7x7. I can see any sign of fatigue in my rigging pretty easily. That is not to say that it's perfect. I do like dux and it may well be the way of the future. It was just more than I could afford at the time and way more than what I ultimately went with. In time, I think dux will get less expensive. I also was not completely confident in how it would hold up over time and my ability to recognize when it needed to be replaced. How does one really know? I would never rule dux out though. I particularly like the new EHLF dux furling system Colligo is selling. Very cool. I'd love to have a test rig of dux on my boat that I could swap out with my current standing rigging setup and compare the performance and ease of tuning. That would be very interesting.

I would also say I have had nothing but great experience with John Franta and Colligo.

[Stumble]

It used to be that Dux was the only game in town, but these days there are real competitors out there. It may be too late now, but I would suggest taking a look at some of the other heat set dyneema ropes out there, some, particularly the Alpha Ropes, are substantially less expensive.

For a side by side comparison see.

http://www.chicagoyachtrigging.com/stretch-test/