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Will an overhand knot in a Dynex runner cut itself under load?
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zewsk


Jun 11, 2012, 5:11 PM
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Will an overhand knot in a Dynex runner cut itself under load?
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I've heard that overhand knots tied in Dynex runners can actually cause the runner to "cut through" itself and sever under load.

Is this true?


cintune


Jun 11, 2012, 6:12 PM
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Re: [zewsk] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
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No.


gunkiemike


Jun 11, 2012, 7:12 PM
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Re: [zewsk] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
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Hang around the Interweb long enough and you'll hear LOTS of things that aren't true.


(This post was edited by gunkiemike on Jun 12, 2012, 2:54 AM)


zewsk


Jun 11, 2012, 7:37 PM
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Re: [gunkiemike] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
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Thanks. I am new to trad and I heard this from a guide at a climbing school. I couldn't find any other evidence to back up the claim.

I'm planning to buy a bunch of runners that I can use for extendable draws and I know I'm going to want to be able to tie knots in them. Aside from the fact that Dynex is hard to untie/untangle compared to nylon, I don't want to end up hurt or dead because I didn't use the proper gear.

Nylon is plenty fine for me. Thanks for the info.


JoeNYC


Jun 11, 2012, 8:26 PM
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Re: [zewsk] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
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this is, i hope, what the guide was talking about:

http://dmmclimbing.com/...notting-dyneema-vid/

edit:

or this:
http://dmmclimbing.com/...ylon-dyneema-slings/


(This post was edited by JoeNYC on Jun 11, 2012, 8:38 PM)


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Jun 11, 2012, 9:39 PM
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Re: [zewsk] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
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Lots of folks are saying no. The answer is yes, in the sense that the sling will be half as strong, and at that level could be catastrophically weak, and yes, it will break at the knot.

The dmm test in http://dmmclimbing.com/...ylon-dyneema-slings/ (also referenced above) shows that a factor-1 fall on a shoulder-length 8mm dyneema sling with an overhand knot in it will break the sling.

I'd say that is a genuine concern. A number of people use the Petzl method of extending the rappel by knotting a dyneema sling girth-hitched to the harness.



Note that Petzl is careful to show the climber hanging on the anchor so that a fall arrested by the tether is not possible. but if you clip this to the rap anchor and, before getting on rappel, fall with your waist even with the anchor, it is possible that the sling would break. (Not guaranteed, because the human body absorbs some fall energy, an 80 kg weight does not).

You say that you know you will want to tie knots. There is now some evidence suggesting that dyneema should not be knotted if there is any chance that it will have to hold even a very short fall.


bearbreeder


Jun 11, 2012, 11:30 PM
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Re: [zewsk] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
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if theres rope in the system ... its not something id worry about ...

if there aint rope in the system ... dont fall on it ...

its that simple Wink


zewsk


Jun 12, 2012, 5:25 AM
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Re: [bearbreeder] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
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I was mostly wondering what the risk would be if I used Dynex slings in my anchors or to extend protection. Both applications would certainly need to take falls.

I do use rappel extensions with double length runners, so that's an option for Dynex.

Honestly, for what I'm climbing, nylon runners should do just fine. It's a bonus that they're cheaper.


bearbreeder


Jun 12, 2012, 10:29 AM
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Re: [zewsk] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
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anchors ... as long as you clove in with the rope youll be fine ...

as runners ... as long as its for a dynamic rope you be fine ...

the only people who go dyneema is "unsafe" is either people who test it for very specific applications ... azzholes .... or newbs ...

i climbed with a guide yesterday who uses a knotted dyneema sling for his anchor ... but then he doesnt take static falls on it ... dont make me post the video of where the canadian rocky mountain rescue hooked up a victim with a knotted dyneema sling ... RCers of course know MUCH better than em Wink

everything is dangerous if used improperly ... the most important thing is to use yr head ...

i find it utterly hilarious when someone tells me how "dangerous" dyneema is ... yet that effer doesnt wear a helmet ... are ya more likely to die from a head trauma or a broken dyneema sling

ill let you be the judge Tongue


dagibbs


Jun 12, 2012, 11:01 AM
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Re: [zewsk] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
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zewsk wrote:
I've heard that overhand knots tied in Dynex runners can actually cause the runner to "cut through" itself and sever under load.

Is this true?

"under load" is far too vague.

Any material will break under sufficient load.

All cord-type materials used in climbing (dynamic or static rope, dyneema or nylon slings, etc) will be weakened by putting a knot in them. All such knotted materials will break under a lower load than the un-knotted material, and they will (almost) always break at the knot.

Does this matter?

Generally, if you have a (dynamic) climbing rope in the load system: no. The shock absorption quality of the rope will keep the load factors on the sling(s) involved to less than the breaking load of either a knotted or un-knotted sling.

If you want to take static falls with a fall-factor approaching or exceeding 1 directly onto a knotted sling -- yeah it might break. An unknotted sling is less likely to break, but even if it doesn't break, you are going to be hurting. You don't want to be in a situation where this could happen, whether your sling is knotted or not.


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Jun 12, 2012, 12:48 PM
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Re: [rgold] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
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For the more visual among us:

http://blip.tv/a-fuerza-de-plafon/dyneema-and-nylon-drop-tests-4509845

Personally, I don't think any sling has a place in my own personal anchoring system, except under rare circumstances. A Dyneema sling with knots in it = double no.


avalon420


Jun 12, 2012, 3:52 PM
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Re: [j_ung] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
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Frown
j_ung wrote:
For the more visual among us:

http://blip.tv/...n-drop-tests-4509845

Personally, I don't think any sling has a place in my own personal anchoring system, except under rare circumstances. A Dyneema sling with knots in it = double no.
I made a clicky, yaaayy !


zewsk


Jun 12, 2012, 5:15 PM
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Re: [j_ung] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
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j_ung wrote:
For the more visual among us:

http://blip.tv/a-fuerza-de-plafon/dyneema-and-nylon-drop-tests-4509845

Personally, I don't think any sling has a place in my own personal anchoring system, except under rare circumstances. A Dyneema sling with knots in it = double no.

This was an awesome video. Thank you so much for sharing this.


Partner rgold


Jun 12, 2012, 7:17 PM
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Re: [bearbreeder] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
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bearbreeder wrote:
anchors ... as long as you clove in with the rope youll be fine ...

Yup.

bearbreeder wrote:
as runners ... as long as its for a dynamic rope you be fine ...

Yup.

bearbreeder wrote:
the only people who go dyneema is "unsafe" is either people who test it for very specific applications ... azzholes .... or newbs ...

By acting like an azzhole yourself here you diminish your point. Nobody that I know of is saying "dyneema is dangerous" without some qualification about when that statement might be true. The qualifications involve the "specific applications" you seem to be dismissing, in spite of the fact that your Canadian guide friend is using the exact specific application DMM was testing.

bearbreeder wrote:
i climbed with a guide yesterday who uses a knotted dyneema sling for his anchor ... but then he doesnt take static falls on it ... dont make me post the video of where the canadian rocky mountain rescue hooked up a victim with a knotted dyneema sling ... RCers of course know MUCH better than em Wink

I haven't seen any RC'ers speaking about rescue practices, which in the case you mention do not involve fall arrests. And the Canadian guide you mention seems to have violated your own standards as you stated them above. So maybe at least some RC'ers know more than you're willing to give credit for, and maybe some Canadian guides know less.

bearbreeder wrote:
everything is dangerous if used improperly ... the most important thing is to use yr head ...

And part of using your head is incorporating knowledge obtained by reputable equipment manufacturers. Not using your head is nattering on about azzholes and ignoring their results.

bearbreeder wrote:
i find it utterly hilarious when someone tells me how "dangerous" dyneema is ... yet that effer doesnt wear a helmet ... are ya more likely to die from a head trauma or a broken dyneema sling

Oh phooey, no one is saying dyneema is dangerous already. (Every one of my quickdraws is dyneema, for example). But there are things you probably shouldn't do with it in the light of the DMM tests, like the Petzl rappel set-up I posted above.

bearbreeder wrote:
ill let you be the judge Tongue

So you can insult the judgers afterwards?

Let's see if we can boil it down. Putting an overhand knot in a dyneema sling that might be involved in arresting a fall is probably a bad idea. Canadian guides please note.


bearbreeder


Jun 12, 2012, 8:40 PM
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Re: [rgold] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
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im sorry ... but are we going off about dyneema again?

i invite you to email petzl and tell them how they should not use the above setup with anything dyneema

i also invite you to ask parks canada why they did it so wrong ...

http://www.youtube.com/watch?v=I7_4n_4Qhu4


(This post was edited by bearbreeder on Jun 12, 2012, 8:41 PM)


Partner rgold


Jun 13, 2012, 6:15 AM
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bearbreeder wrote:
im sorry ... but are we going off about dyneema again?

You started the "going on" part and then invited its continuation.

bearbreeder wrote:
i invite you to email petzl and tell them how they should not use the above setup with anything dyneema

Will do.

bearbreeder wrote:
also invite you to ask parks canada why they did it so wrong ...

Don't have too---the film you referenced was made two years before the DMM tests. What seemed like ok practice then seems less ok now. I guess it would be interesting to find out whether Parks Canada rescue personnel are still using knotted dyneema tethers; I'll leave that email assignment to you.
Meanwhile, could we inspect the logic here, after all, you seem to be a fan of "using yr head." People use tethers in situations in which a fall would be catastrophic, and in which it is conceivable that a fall could happen (it a fall is inconceivable, no need for a tether, right?). Why, in that circumstance, would anyone use a knotted tether that breaks in testing in a very likely fall scenario for that usage, namely a fall with a small amount of slack with the waist at the level of the anchor? Please explain the logic behind that choice.


bearbreeder


Jun 13, 2012, 8:08 AM
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its quite simple ... you dont take a static fall ... period ...

if you think yr going to take a static fall ... retie in with the rope and clove in ... static falls are BAD regardless of what you use ... this isnt via ferrata ... if you think youll be taking a static fall on a good portion of the climb, use a via ferrata type lanyard

train yourself to not have slack in the system when clipped in no matter what gear you use

i personally use a PAS, and as we all know they wont take a factor 2 fall ... do i care? ... nope im not taking a factor 2 fall on it ... i find it utterly hilarious when some guy at the crag started rambling on about how "unsafe" my PAS is because it wont a factor 2 fall when they use a nylon sling or a beal dyna connection and have enough slack in the system for a factor 1 fall

the "flaw" you pointed out on the petzl diagram is a non issue if you simply keep slack out of the system ...

the most important thing is to use yr head ... plenty of guides or other experienced individuals i know use slings for personal rap anchors simply because they dont believe in carrying up extra gear ... and often those are dyneema slings ... hell many sport climbers will do the same with linked draws, sometimes dyneema ones, are they doing to die too? ... they know better than to take a static fall on em

weight that tether and keep the slack out of the system ... thats the logic ... and if its ever an issue, tie in with the rope

dont take a static fall regardless of what material you use

and dont be one of those RCers who shout out that PASes, daisies, dyneema, etc ... are unsafe ... everything is unsafe if used a certain way


shockabuku


Jun 13, 2012, 9:01 AM
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bearbreeder wrote:
its quite simple ... you dont take a static fall ... period ...

if you think yr going to take a static fall ... retie in with the rope and clove in ... static falls are BAD regardless of what you use ... this isnt via ferrata ... if you think youll be taking a static fall on a good portion of the climb, use a via ferrata type lanyard

train yourself to not have slack in the system when clipped in no matter what gear you use

i personally use a PAS, and as we all know they wont take a factor 2 fall ... do i care? ... nope im not taking a factor 2 fall on it ... i find it utterly hilarious when some guy at the crag started rambling on about how "unsafe" my PAS is because it wont a factor 2 fall when they use a nylon sling or a beal dyna connection and have enough slack in the system for a factor 1 fall

the "flaw" you pointed out on the petzl diagram is a non issue if you simply keep slack out of the system ...

the most important thing is to use yr head ... plenty of guides or other experienced individuals i know use slings for personal rap anchors simply because they dont believe in carrying up extra gear ... and often those are dyneema slings ... hell many sport climbers will do the same with linked draws, sometimes dyneema ones, are they doing to die too? ... they know better than to take a static fall on em

weight that tether and keep the slack out of the system ... thats the logic ... and if its ever an issue, tie in with the rope

dont take a static fall regardless of what material you use

and dont be one of those RCers who shout out that PASes, daisies, dyneema, etc ... are unsafe ... everything is unsafe if used a certain way

WTF is a "static fall"?


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Jun 13, 2012, 2:34 PM
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shockabuku wrote:
bearbreeder wrote:
its quite simple ... you dont take a static fall ... period ...

if you think yr going to take a static fall ... retie in with the rope and clove in ... static falls are BAD regardless of what you use ... this isnt via ferrata ... if you think youll be taking a static fall on a good portion of the climb, use a via ferrata type lanyard

train yourself to not have slack in the system when clipped in no matter what gear you use

i personally use a PAS, and as we all know they wont take a factor 2 fall ... do i care? ... nope im not taking a factor 2 fall on it ... i find it utterly hilarious when some guy at the crag started rambling on about how "unsafe" my PAS is because it wont a factor 2 fall when they use a nylon sling or a beal dyna connection and have enough slack in the system for a factor 1 fall

the "flaw" you pointed out on the petzl diagram is a non issue if you simply keep slack out of the system ...

the most important thing is to use yr head ... plenty of guides or other experienced individuals i know use slings for personal rap anchors simply because they dont believe in carrying up extra gear ... and often those are dyneema slings ... hell many sport climbers will do the same with linked draws, sometimes dyneema ones, are they doing to die too? ... they know better than to take a static fall on em

weight that tether and keep the slack out of the system ... thats the logic ... and if its ever an issue, tie in with the rope

dont take a static fall regardless of what material you use

and dont be one of those RCers who shout out that PASes, daisies, dyneema, etc ... are unsafe ... everything is unsafe if used a certain way

WTF is a "static fall"?

Oh no...

GFrown


jt512


Jun 13, 2012, 8:49 PM
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shockabuku wrote:
bearbreeder wrote:
its quite simple ... you dont take a static fall ... period ...

if you think yr going to take a static fall ... retie in with the rope and clove in ... static falls are BAD regardless of what you use ... this isnt via ferrata ... if you think youll be taking a static fall on a good portion of the climb, use a via ferrata type lanyard

train yourself to not have slack in the system when clipped in no matter what gear you use

i personally use a PAS, and as we all know they wont take a factor 2 fall ... do i care? ... nope im not taking a factor 2 fall on it ... i find it utterly hilarious when some guy at the crag started rambling on about how "unsafe" my PAS is because it wont a factor 2 fall when they use a nylon sling or a beal dyna connection and have enough slack in the system for a factor 1 fall

the "flaw" you pointed out on the petzl diagram is a non issue if you simply keep slack out of the system ...

the most important thing is to use yr head ... plenty of guides or other experienced individuals i know use slings for personal rap anchors simply because they dont believe in carrying up extra gear ... and often those are dyneema slings ... hell many sport climbers will do the same with linked draws, sometimes dyneema ones, are they doing to die too? ... they know better than to take a static fall on em

weight that tether and keep the slack out of the system ... thats the logic ... and if its ever an issue, tie in with the rope

dont take a static fall regardless of what material you use

and dont be one of those RCers who shout out that PASes, daisies, dyneema, etc ... are unsafe ... everything is unsafe if used a certain way

WTF is a "static fall"?

A downward "static move"?

Jay


shockabuku


Jun 14, 2012, 7:48 AM
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jt512 wrote:
shockabuku wrote:
bearbreeder wrote:
its quite simple ... you dont take a static fall ... period ...

if you think yr going to take a static fall ... retie in with the rope and clove in ... static falls are BAD regardless of what you use ... this isnt via ferrata ... if you think youll be taking a static fall on a good portion of the climb, use a via ferrata type lanyard

train yourself to not have slack in the system when clipped in no matter what gear you use

i personally use a PAS, and as we all know they wont take a factor 2 fall ... do i care? ... nope im not taking a factor 2 fall on it ... i find it utterly hilarious when some guy at the crag started rambling on about how "unsafe" my PAS is because it wont a factor 2 fall when they use a nylon sling or a beal dyna connection and have enough slack in the system for a factor 1 fall

the "flaw" you pointed out on the petzl diagram is a non issue if you simply keep slack out of the system ...

the most important thing is to use yr head ... plenty of guides or other experienced individuals i know use slings for personal rap anchors simply because they dont believe in carrying up extra gear ... and often those are dyneema slings ... hell many sport climbers will do the same with linked draws, sometimes dyneema ones, are they doing to die too? ... they know better than to take a static fall on em

weight that tether and keep the slack out of the system ... thats the logic ... and if its ever an issue, tie in with the rope

dont take a static fall regardless of what material you use

and dont be one of those RCers who shout out that PASes, daisies, dyneema, etc ... are unsafe ... everything is unsafe if used a certain way

WTF is a "static fall"?

A downward "static move"?

Jay

Then I have to assume that, for the most part, it is only influenced by "static gravity".

Actually, that almost makes some sense.


(This post was edited by shockabuku on Jun 14, 2012, 8:02 AM)


herites


Jun 15, 2012, 3:57 PM
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1: Clip a draw to the anchor
2: Clove in
3: Clip knotted nylon sling to anchor and weigh it
4: Rig your Petzl-style rap

With the clove hitch you won't die if you somehow manage to fall onto the sling and break it, and I like to secure the rope to the anchor anyway, I've had seen dropped ropes because the climber didn't secure the rope before threading the anchors, just untied and dropped it.


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Jun 21, 2012, 12:55 PM
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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.



bearbreeder


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thats basically my viewpoint ... dont get yourself where youll fall onto static material ... like i said ive seen people with beal dynaconnections, purcell prussics, etc introduce slack into the system because they are "confident" itll save their azzes ... the proper way IMO is to develop the habit on not putting yrself in that position

there are many things thats people worry about on RC, that in the real world we just deal with normally ... stuff like PASes, daisies, 7-8 kn biners, fancy TR anchor setups, etc ... those really arent the things that are likely to kill you

rapping off ends, getting dropped, taking a ground fall, not wearing a helmet, etc ... those are the things that will likely get you

most manufacturers do not seem too worried about what RCers go off about ...

and no insult intended to anyone on this thread


fresh


Jul 2, 2012, 12:26 PM
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Re: [rgold] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
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James Good wrote:
if you do need to move while at a belay you should avoid a fall factor 1 or greater
heh, thanks dude.

also, the link he references is dead now.


splish


Jul 21, 2012, 10:43 PM
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Re: [zewsk] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
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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
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Re: [rgold] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
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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
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Re: [FullertonImages] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
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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
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Re: [rgold] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
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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
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Re: [kennoyce] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
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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
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Re: [rgold] Will an overhand knot in a Dynex runner cut itself under load? [In reply to]
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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.


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