Consensus on knots in slings
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Heres my questions: |
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You'd have to generate ALOT of force (mainly static) to cause failure at a knot in a sling. |
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Good question. |
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That book is not outdated. It is one of the most up to date books out there. |
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It has to do with material. Nylon slings are fine to be knotted. Dyneema and spectra should not be knotted because the material is brittle and it will weaken the sling. That being said, assuming you knot a dyneema sling and use it for top roping, generating little force, or other low force situation, it would probably be okay. Its a problem with people use dyneema slings for the personal safeties, tie a knot in it and then fall on the sling from a point above the anchor. Drop test in these situations have shown failures. |
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Gretchen is 100% right.. a knotted Dyneema is asking for trouble..that said. a nice tight water knot in a say, 11/16" nylon is fine..weight it hard |
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Tying a know in a rope weakens it too. How much? There are easy mathematical equations so you can decide your acceptance level. The one difference though is dyneema. Since dyneema has such a low melting point there have been failures when tying knots in it which is of course different than lowering the overall strength by X percent. I will never tie a know in dyneema but will in nylon if necessary. |
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john strand wrote:Gretchen is 100% right.. a knotted Dyneema is asking for trouble..that said. a nice tight water knot in a say, 11/16" nylon is fine..weight it hard I always have one knotted sling..your really don't want to leave behind your nice new $9 sling ?100% wrong you mean. In what way is dyneema "brittle". Like a piece of ice? |
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I guess it just seems sketchy to me to put in a climbing anchor book pictures of knotted slings (can't tell if they are nylon or dyneema) and call them "ideal". I understand its a give and take, but the fact that it was confusing to me makes me think it might not be the best presentation- especially since this debate is not mentioned. If there was a more thorough discussion of this topic in the book, perhaps. But as it is... |
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it is..nylon is soft |
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rging wrote: 100% wrong you mean. In what way is dyneema "brittle". Like a piece of ice?http://en.wikipedia.org/wiki/Brittleness Brittle has a technical definition, which is pretty close to my understanding of how the high strength polymers used in climbing behave. |
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edennis wrote:I guess it just seems sketchy to me to put in a climbing anchor book pictures of knotted slings (can't tell if they are nylon or dyneema) and call them "ideal". I understand its a give and take, but the fact that it was confusing to me makes me think it might not be the best presentation- especially since this debate is not mentioned. If there was a more thorough discussion of this topic in the book, perhaps. But as it is...Again... Sometimes knotting your sling minimizes extension or adds redundancy if there is reason to believe the sling will be abraded. If Craig Luebben says the setup is ideal, the setup is ideal. The knot serves a purpose. Consider also what is a pretty common (and completely safe) rappel and backup setup, which is to girth a double runner to your tie in points and knot it halfway. Your backup goes on your belay loop, and your rappel device goes at the knot. The remainder of the sling allows you to clip the next anchor. Removing the knot from the sling wouldn't make this setup more ideal. It's perfectly fine with the knot in there, and the knot adds to the functionality of the setup. You knot (and weaken) your climbing rope all the time. |
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rging wrote: In what way is dyneema "brittle".Brittle may not be the best term. Nylon stretches a little so even though its strength rating is less than dyneema and spectra, it absorbs the energy over more time so it is less likely to break on a static fall. Dyneema and spectra have no stretch at all so they absorb all the energy of a static fall in one instant. The end result is that dyneema and spectra will break on a factor 2 static fall if they are knotted, but nylon won't. There's test videos out there if you search it. This is why both of those materials warn against using knots. Of course, taking a factor 2 static fall may make you wish you were dead anyway. |
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Doug S wrote: Brittle may not be the best term.Brittle is the precise technical term for materials that break without significant deformation, of which dyneema and spectra are two examples. |
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so are we assuming everyone that's using dyneema slings for their trad anchors is going to fall to their deaths? |
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Xam... you are exactly right, sir. Didn't know it was a technical term. Cool. |
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Not entirely the same question, but still I think some useful info on webbing on webbing behavior blackdiamondequipment.com/e… |
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Rob Davis wrote:so are we assuming everyone that's using dyneema slings for their trad anchors is going to fall to their deaths?That seems to be the consensus. Things you learn on mountainproject... |
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In the history of climbing, has anyone ever died because they used a dyneema sling instead of a "dynamic" nylon runner? Sounds to me like the kind of thing that only happens in internet climbing land. |
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I always found this informative: user.xmission.com/~tmoyer/t… |
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Does keeping the knot in a sewn nylon sling weaken it more? |