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post #15 of Old 04-25-2019
Jeff_H
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Re: Tether overload protection

Quote:
Originally Posted by pdqaltair View Post
No, Not ever. Dynemma is acceptable for jacklines, but NOT for tethers.

The ISAF and ISO standards include a drop test and require some level of shock absorption. There are reasons no commercial tether is made of anything other than nylon.

Try this test. Make a tether out of something non-stretch like Dyneema, tie it to a tree, gather up some slack, and take a run at it. If you leave more than 2 feet of slack you are going to get bruises, and with 4 feet of slack, expect a back injury or cracked ribs.

Tethers must ALWAYS have some stretch.

---

There are two VITAL shortcomings with the Sailrite testing:
1. They tested polyester webbing, which does not stretch. Sewing a material that stretches, like nylon, requires a different method. It's like sewing elastic. A box stitch is not used for this application, so the formula and testing is not valid.
2. Nylon is always bar tacked. Look at ANY climbing equipment. There are engineering reasons for this that have NOTHING to do with economy.
(I used to be in the industry and have tested sewn nylon--I'm not guessing or reading off the net)

They very wisely stopped selling the harness and tether kits. They did not meet any of the required standards. They are sailmakers, not structural equipment fabricators.
Thank you for posting this. I think most of us come here to be helpful and to learn from those who know more about a subject than we do. I had always assumed that if i ever made a tether it would be a nylon tube over a dyneema core with the dyneema spliced to the hardware and with a shock chord in the tube acting as a retracter. In my ignorance, it never occurred to me that it was possible that there could be too little stretch to a tether. I really appreciate your explanation. Live and learn.

Reading that, it sounds like if someone had to make their own tether, the core would want to be something like 3/8" diameter 3-strand polyester or even nylon spliced to the hardware with the tubing reducing slip potential and providing a UV screen rather than a structural component. On the other hand, the case that you clearly make suggests that making your own tether is simply a bad idea.

For what it is worth, I use an 11 mm kevlar cored line as my jacklines and hook onto the windward line thinking that they would prevent me from making it over the leeward toerail. (So far they have) It sounds like that isn't a great idea either.

Jeff


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Last edited by Jeff_H; 04-25-2019 at 08:48 AM.
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