Forums: Climbing Disciplines: Trad Climbing:
Will an overhand knot in a Dynex runner cut itself under load?
RSS FeedRSS Feeds for Trad Climbing

Premier Sponsor:

 
First page Previous page 1 2 Next page Last page  View All


splish


Jul 21, 2012, 10:43 PM
Post #26 of 31 (1212 views)
Shortcut

Registered: Aug 21, 2005
Posts: 140

Re: [zewsk] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

Well, I don't own any dynemma, I use nylon and cordlettes for my anchors, draws, hexes and so on. But I learned a few things from this post.

First and foremost, it seems nobody really know anything about Dyneema.

Second, Dyneema has a very shitty Impact Force rating. I understand that my Dynamic Rope will take most of the impact force, but as a trad climber, I can use all the help I can get, so having my slings and dog bones absorb a little more of the force is a wonderful thing.

And finally, after watching the DMM tests ,I will not be in any hurry to go out and buy any Dyneema. Yes, in a sewn sling, it has all the strength of nylon at less weight, but quite frankly, it seems useless to me to carry something that you can't knot seeing as more than half our sport is all knots, and I don't really want to carry anything that loses so much strength just from a knot.

In the first video, those knots were slipping in the Dyneema just from static force. What if you were in a situation where you needed to cut your 120 sling to make a 240 runner. You can't even tie loops in the end?

You guys can go on fighting this out till you are blue in the face, but in the end, it's going to be a personal preference depending on what you feel confident with.

UIAA has done their safety tests, and obviously the stuff has passed, or it wouldn't be on the market.


FullertonImages


Aug 14, 2012, 7:53 AM
Post #27 of 31 (1078 views)
Shortcut

Registered: Jan 30, 2009
Posts: 40

Re: [rgold] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

rgold wrote:
Here is the result of the inquiry to Petzl I promised to do. I wrote,

Your advice about rappel technique recommends the use of a sling girth-hitched to the harness with an overhand knot halfway along. Recent tests by DMM, http://dmmclimbing.com/...ylon-dyneema-slings/, have shown that Dyneema slings in this configuration might break in a factor-1 fall, even when the sling and fall distance are very short. This is a possible scenario when anchoring with the Petzl method prior to rappelling. I am interested in whether you consider this to be a genuine concern.

Thanks for any help and insight you can provide.

The reply is from James Good, Petzl America, Technical Quality Assurance, Warranty and Returns Manager

Absolutely, Petzl is concerned regarding a fall on any static lanyard onto an anchor whether you have an overhand knot in the lanyard or not.

I first want to point out that you should never put yourself in position for any type of fall when positioned directly into the anchor. if you do need to move while at a belay you should avoid a fall factor 1 or greater due to the impact forces you can generate. This information accompanies all of our lanyard technical notices and is also found online, http://www.petzl.com/...t/C06-FIN-ANNEAU.pdf (Third panel down--RG)

As a suggestion, when multi pitch climbing Petzl recommends an overhand knot in the middle of a 120cm lanyard girth hitched through the double tie-in points to assist the climber by extending the rappel device off of the belay loop and at the same time allowing you to still be connected into the anchor, http://www.petzl.com/...ing_Catalog-2012.pdf (page 18 and page 19).

Keep in mind regarding the DMM tests that these tests were performed with a static mass falling vertically off of a static anchor point and completely free of any obstruction once in flight. These labs tests are accurate and a great learning tool but when in the field and when you introduce a harness and the human body into the system the impact forces will be decreased because of the stretch of the harness, rope, and body of the climber, etc.

That's basically how I feel. Even though it's quite disheartening to see the dynes a slings break in a factor 1 fall when knotted, I also feel like it would virtually impossible to apply that much force at a belay/rappel station. I the drop test, the mass free falls with no friction, then absorbs essentially 0% of the force, transferring it all to the sling. In real life, there will almost always be friction, from sliding down the face if you slipped, you may catch something with your hand to slow you, and you body/harness absorb a good bit of the shock load. To replicate this test in the file you would have to be at a very overhanging rappel (???), find some hold to pull up onto so you waist is even with the anchor, then suddenly let go, at which point you body and harness would still absorb some of the fall.

I'm all for drop tests and the knowledge they produce, and this is definitely something I will keep in mind in regards to dyneema, knots and belays/rappers, but I also see the likelihood of this happening in the field as pretty darn low.

Does anyone know of instances where dyneema broke in a real world usage due to failure at a knot? I have not heard of any. (this is a legitimate question, not some kind of passive aggressive blah blah blah...)


Partner rgold


Aug 14, 2012, 8:23 AM
Post #28 of 31 (1067 views)
Shortcut

Registered: Dec 3, 2002
Posts: 1800

Re: [FullertonImages] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

I think the subject is riddled with double-think. People clip in with a tether in order to protect against the consequences of a fall and then go on about how you better not fall, and if you do you were misusing the tether.

Can a climber fall off a small belay ledge and break a knotted dyneema tether? We don't know the answer to that. Human body loads are less than the ones you get from steel weights, probably because all parts of the human body do not generally come to rest at the same time.

Energy absorbtion by the harness is probably nil, and the limited range of displacement of the human body means there isn't a lot of energy absorbing capability there either. So it probably comes down to how the limbs are arranged at fall impact, and this means a considerable variation in the possibilities, including possibly something with results close to the steel weights.

I've never heard of knotted dyneema breaking in the real world. But like certain other things climbers guard against, we are speaking of things---falling off a belay stance---that happen extremely rarely, meaning we don't have the real-world experience to know anything about this, which is the point of the tests in the first place.

But in any case, I think reasoning about this is generally clouded. Tests, which may be overly severe, show that nylon is far better than dyneema for tethers. Given that indisputable fact, why would one choose to use dyneema tethers when it is just as easy and typically cheaper to use nylon ones, citing first the need to never apply the loads the tether is supposed to guard against and second fairly uninformed intuitions about the relevance of the tests?

There might be a response for winter applications, where dyneema's resistance to water absorbtion is advantageous. But for most rock and alpine ascents, why not just use a nylon tether?


kennoyce


Aug 14, 2012, 10:52 AM
Post #29 of 31 (1035 views)
Shortcut

Registered: Mar 6, 2001
Posts: 1303

Re: [rgold] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

rgold wrote:
I think the subject is riddled with double-think. People clip in with a tether in order to protect against the consequences of a fall and then go on about how you better not fall, and if you do you were misusing the tether.

Can a climber fall off a small belay ledge and break a knotted dyneema tether? We don't know the answer to that. Human body loads are less than the ones you get from steel weights, probably because all parts of the human body do not generally come to rest at the same time.

Energy absorbtion by the harness is probably nil, and the limited range of displacement of the human body means there isn't a lot of energy absorbing capability there either. So it probably comes down to how the limbs are arranged at fall impact, and this means a considerable variation in the possibilities, including possibly something with results close to the steel weights.

I've never heard of knotted dyneema breaking in the real world. But like certain other things climbers guard against, we are speaking of things---falling off a belay stance---that happen extremely rarely, meaning we don't have the real-world experience to know anything about this, which is the point of the tests in the first place.

But in any case, I think reasoning about this is generally clouded. Tests, which may be overly severe, show that nylon is far better than dyneema for tethers. Given that indisputable fact, why would one choose to use dyneema tethers when it is just as easy and typically cheaper to use nylon ones, citing first the need to never apply the loads the tether is supposed to guard against and second fairly uninformed intuitions about the relevance of the tests?

There might be a response for winter applications, where dyneema's resistance to water absorbtion is advantageous. But for most rock and alpine ascents, why not just use a nylon tether?

I generally agree with you, but I don't agree that people clip in with a tether to protect against a fall. The only time that I use tethers (and most people I know are the same) is when cleaning the anchors on a single pitch route. In this case, you are weighting the teathers the whole time and not moving around or unweighting them which would be required to fall onto them. The only time you unweight the tethers are when you are once again connected to the rope. In this aplication I see no advantage to using nylon other than price.


csproul


Aug 14, 2012, 11:29 AM
Post #30 of 31 (1028 views)
Shortcut

Registered: Jun 4, 2004
Posts: 1767

Re: [kennoyce] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

People use tethers all the time to anchor in while rappelling. Often, to reach the rap anchors people will clip in above (e.g. from the top of the cliff) and ease over the lip to hang on the anchors. I see it all the time around here. Hell, I do it pretty often even though I know it's not the greatest idea in the world. It is in cases like this that I can see why nylon would be advantageous. Nylon daisies for aid climbing also come to mind for that rare daisy fall.


ptlong2


Aug 14, 2012, 5:34 PM
Post #31 of 31 (994 views)
Shortcut

Registered: Aug 10, 2010
Posts: 102

Re: [rgold] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (1 rating)  
Can't Post

rgold wrote:
Tests, which may be overly severe, show that nylon is far better than dyneema for tethers. Given that indisputable fact, why would one choose to use dyneema tethers when it is just as easy and typically cheaper to use nylon ones, citing first the need to never apply the loads the tether is supposed to guard against and second fairly uninformed intuitions about the relevance of the tests?

Because the tests are probably overly severe. Show us the data that demonstrate otherwise.

The tether is not there to guard against the kind of extreme loads that could actually break it. It's there to keep you from falling off the belay. And if you're wise you'll clip in redundantly, not because the sling might break from a fall but because of potential human error. Broken tether? Show us a single case in all of climbing history!


rgold wrote:
why not just use a nylon tether?

Because spectra and dyneema are lighter and less bulky.

Not everybody carries a dedicated tether. I use slings, the same ones I use for other purposes. They are almost all spectra/dyneema.

I'm not worried.

First page Previous page 1 2 Next page Last page  View All

Forums : Climbing Disciplines : Trad Climbing

 


Search for (options)

Log In:

Username:
Password: Remember me:

Go Register
Go Lost Password?
$8.96 (10% off)
$21.56 (10% off)
$107.96 (10% off)
$621.00 (10% off)



Follow us on Twiter Become a Fan on Facebook