Consensus on knots in slings

Heres my questions:

From what I have seen online, specifically dmm's "how to break nylon and dyneema slings" and others like it, it seems obvious that putting knots in slings is a really poor choice and can compromise the sling strength.

that said, I recently bought this book as per a recommendation:
rei.com/zoom/t/1158378.jpg/440

In this book, the author is constantly referring to anchors using slings with knots in them- even calling them "ideal". Is the info in this book outdated?

What gives?

Thanks in advance for helping a beginner.

Regards,
-Eric

You'd have to generate ALOT of force (mainly static) to cause failure at a knot in a sling.

I've used overhand knots in slings for an array of circumstances while climbing, mostly while traditional and aid climbing when improvisation skills are key.

I've seen the same DMM videos your speaking of. Very interesting stuff.

I'm sure someone else probably has better information than I do. I'd also like to hear other folks opinion and thoughts on this.

On a side note, Freedom of the Hill is a great all around book to acquire.

Good question.

Because tying a knot in webbing weakens the webbing, it should be avoided when not necessary. I think good candidates for "not necessary" are instances where a climber chooses to tie knots instead of getting cams reslung (although my rack has a few of those).

However, there are times when you need to create a loop out of a length of webbing while climbing, and at those times a knot is necessary. Understand that it weakens the webbing (and understand by how much), and take that into account. Consider bringing longer sewn slings where they will work.

There are also times when knots should be incorporated in an anchor to reduce extension. In those situations, weigh the negative consequences of the extension that could happen vs the weakening of the sling that does happen, as well as how likely either is to matter.

That book is not outdated. It is one of the most up to date books out there.

As with anything, there are tradeoffs. Sometimes knotting your sling minimizes extension or adds redundancy if there is reason to believe the sling will be abraded. Yes, a knot will reduce the breaking strength of the webbing. However, sewn slings are rated to at least 22 kN. Cutting that by a third still puts you at well over the maximum force you would expect to put on an anchor. Plus, there is redundancy in the anchors he describes.

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.

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 ?

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.

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?

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...

it is..nylon is soft

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.

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.

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.

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.

so are we assuming everyone that's using dyneema slings for their trad anchors is going to fall to their deaths?

Xam... you are exactly right, sir. Didn't know it was a technical term. Cool.

I use some dyneema slings and I think they are great, but I don't knot them. Using them with a dynamic rope makes it highly unlikely that you could generate enough force to break them.

I'm pretty sure nylon and titan are fine to knot/hitch.

Not entirely the same question, but still I think some useful info on webbing on webbing behavior blackdiamondequipment.com/e…

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...

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.

But I could be wrong.

I always found this informative: user.xmission.com/~tmoyer/t…

I think the main knot I'd tie in skinny slings would be a slip knot - I wonder how that affects them?
My double length runners and cordelette are nylon. Knot well and cheap enough to cut up and leave behind if needed.

Does keeping the knot in a sewn nylon sling weaken it more?

I use a 24" sewn sling girth hitched to my tie in points, with an overhand in the middle as a pas and for extending rappels, i keep it tied and on my harness at all times because the knot is so hard to undue all the time. How long do you think i should keep this setup before retiring? maybe its just time for a real pas.