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swebster
May 10, 2006, 2:58 PM
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In reply to: So it seems we're still looking for a good solution of anchoring oneself when fiddling around at a rapell station (i.e. you can't use the ropes to anchor yourself).
You can use the rope! It is probably the "best" option and will result in lower forces than if you use any of the other stuff on your rack, but you still need to be careful because you could still generate relatively high forces, even with the rope... possibly enough to break a cross-loaded biner for instance.
It's just that there is no sort of magical way to prevent that, we need to accept it and try not to do stupid things at belay stations (like take factor 2 falls while fiddling around). Personally, I try to always have my tie in to the anchor weighted... that way I can't fall at all.
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sterlingjim
May 10, 2006, 3:26 PM
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In reply to: Actually, I think neither will break in a real life situation. The person in the harness absorbs a lot of energy. It is clear that if you do a drop test with a rigid load, then basically the only thing that determines the force is the "rope" material... but if there is a person in a harness, they absorb a lot of energy regardless of the material. Unfortunately this is all hard to test since people don't like being dropped like this, and the way they land can affect the forces etc.
All true. The ratio between the rigid test and a live person test will remain constant however. It would be great to do live tests but I'm just too afraid. I've had two serious back surgeries and not keen on any more.
Yeah, yeah, I did the test with runners already. I forgot for some reason. I was thinking this was a slightly different scenario. I've been testing/breaking too many things lately. :oops:
Then again the 0.5m you mentioned is a tad bit different, a little shorter drop. For now I'll do an equivalent rope length including knots (pretensioned).
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dingus
May 10, 2006, 3:38 PM
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In reply to: .It is obvious that a lot of climbers (especially sport climbers) want something quick, easy, and adjustable to anchor into at the top of a route..
For most of the sport climbers I know, a couple of draws suffice for anchoring in prior to the lower off.
In trad I am certainly used to a bunch of gear on my harness and over the shoulder. Its part of the gig.
I've found having extra crap on my harness when sport climbing is a distraction and sometimes literally causes problems, ie getting in the way.
If I think I'll need to hang at the anchors for an extended period I would take something extra to anchor in, a girthed shoulder sling most likely. But for the typical sport send where I might spend a minute at the anchors rigging the lower off? Draws suffice.
DMT
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swebster
May 10, 2006, 3:48 PM
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In reply to: All true. The ratio between the rigid test and a live person test will remain constant however. It would be great to do live tests but I'm just too afraid. I've had two serious back surgeries and not keen on any more.
The assumption that the ratio between a rigid test and a live test will be constant is incorrect, in my opinion.
It depends on what the limiting factor is in each case. I think that for short rope lengths, the person is doing the majority of the absorption, so the rope material matters less. As the rope length gets longer, the person becomes irrelevant, and it is all about the rope material.
A couple people I work with and I made up this model where the rope and the person are both modelled by Hooke's law springs, found spring constants for various things using some of the forces we found in this forum and in the rock and ice study, and it seems to agree with my argument. The spring constant of the person stays the same, but the spring constant of the rope varies with length, then you add them "in parallel" to find the effective spring constant of the system, and solve for the force. At very short rope lengths the spring constant of the rope is irrelevant, and at very long rope lengths the spring constant of the person is irrelevant.
It's just too complicated to put into a message on this forum, and I certainly wouldn't want to be the person in the drop tests either :)
What device do you use to measure the forces? If I could get my hands on one I bet I could get one of my friends to do the tests. He is even more insistent that the person does all the absorbing than I am.
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heiko
May 10, 2006, 4:07 PM
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In reply to: In reply to: So it seems we're still looking for a good solution of anchoring oneself when fiddling around at a rapell station (i.e. you can't use the ropes to anchor yourself). You can use the rope!
On a multi-pitch rapell, how would I do that?
I rapell one pitch, arrive at the belay; the ropes go through my belay device and my backup friction knot, i.e. the rope between the belay device and the top anchor is under tension. The rest of the two strands of rope are dangling down in space or are in a rope bucket or whatever.
How can I now use the ropes to anchor myself? Do I use the tails? If I hang on the tails somehow, how would I release my belay device and friction knot? Even if I manage to do that, I can't pull the ropes anymore to set up the rapell for the next pitch, because they're attached to me.
I think I just don't get it.
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can_climber
May 10, 2006, 4:17 PM
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Well,
you don't have to use "the" rope. But you can use "a" rope...about 1.5m long that is tied to you and cloved through a biner.
As far as comparing all the different single line anchoring methods, the rope was the only one that did not break. So it looks like the best option in a bad situation. The less my back has to absorb the better. But we are all wise to avoid bad situations, and have redundancies in place for the unlikely possibilities.
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heiko
May 10, 2006, 4:31 PM
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double post.
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heiko
May 10, 2006, 4:41 PM
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How about this (for a two bolt setup):
girldrifter mentioned this piece of rope with a loop tied at each end (maybe with a fig8 on a bight or similar), I think it's called a lanyard.
Now... one loop gets attached to the harness. The other loop gets attached to bolt 1 with a locker. Somewhere along the rope you tie a clove hitch on a locker on bolt 2, and conveniently adjust your distance to the anchor.
Like this one would be using dynamic rope, and have a backup.
:?:
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swebster
May 10, 2006, 4:55 PM
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In reply to: On a multi-pitch rapell, how would I do that? I rapell one pitch, arrive at the belay; the ropes go through my belay device and my backup friction knot, i.e. the rope between the belay device and the top anchor is under tension. The rest of the two strands of rope are dangling down in space or are in a rope bucket or whatever.
Sorry heiko, I didn't read your post carefully enough. I think you're right that in the case of rapelling like this, using the rap rope is not going to happen. Personally I think it is fine to anchor using slings in this case. Keep in mind that there is some (in my opinion relatively small) increased risk of a major load when doing this.
You could carry around a spare piece of dynamic rope, but that sounds too inconvenient to me.
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sterlingjim
May 10, 2006, 7:03 PM
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So……, 24” (0.61m) from end of fig 8 loop to end of fig 8 loop of 10.2mm dynamic rope pre-tensioned with the 80kg. 48” (1.22m) drop. Impact force = 7kN(6.98 actual). Granted this was only one drop sample; all I had time for right now. The published impact rating of this rope is 8.8kN. The standard drop test is FF 1.77 on 2.8m of rope.
I may be willing to take this fall myself……. maybe. Have to find a safe place to set it up.
I don't have time to really think about this right now but thought you guys might like something to chew on.
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heiko
May 10, 2006, 9:57 PM
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In previous posts you mentioned that on subsequent falls the rope would break at the knots. This would certainly be a problem for the proposal I made a bit earlier today.
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sterlingjim
May 11, 2006, 3:19 AM
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In reply to: In previous posts you mentioned that on subsequent falls the rope would break at the knots. This would certainly be a problem for the proposal I made a bit earlier today.
Man I'm an idiot. Yeah, those previous posts were about drop tests which were essentially the same as the one I did today.
Yes, they break at the knot. The impacts are considerably more survivable than the slings, nylon or spectra.
I'm not exactly sure there is one single ideal system for anchoring at rappel stations. I will confess I use spectra/dyneema slings for this myself or whatever else I may have at hand. My preference is a hunk of 6 or 7mm cord.
swebster is absolutely right about the human body absorbing a great deal of the force. Someone with a lot more physics savvy than I can probably sort out just how much that might be.
I think what is the most important thing is for people to be aware of the limitations of the materials they are using as well as their own body.
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papounet
May 11, 2006, 11:46 AM
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In reply to: swebster is absolutely right about the human body absorbing a great deal of the force. Someone with a lot more physics savvy than I can probably sort out just how much that might be. I think what is the most important thing is for people to be aware of the limitations of the materials they are using as well as their own body.
A bit of historic research would surely bring to your attention how the maximum force 12kn was choosen by the UIAA. They "simply" decided to extrapolate the results from tests done by Military forces, which had determined that sudden deceleration of more than 12g lead to injuries.
They decided to require that dynamic ropes do not subject a climber to such decelleration.
Industrial safety experts have looked into the data and elected to choose 6kn as the maximum force a rope should be allowed to impose on the faller.
The deformation of the body has thus been quite researched, such as
http://www.hse.gov.uk/...df/2003/hsl03-09.pdf
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sterlingjim
May 11, 2006, 1:31 PM
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In reply to: In reply to: swebster is absolutely right about the human body absorbing a great deal of the force. Someone with a lot more physics savvy than I can probably sort out just how much that might be. I think what is the most important thing is for people to be aware of the limitations of the materials they are using as well as their own body. A bit of historic research would surely bring to your attention how the maximum force 12kn was choosen by the UIAA. They "simply" decided to extrapolate the results from tests done by Military forces, which had determined that sudden deceleration of more than 12g lead to injuries. They decided to require that dynamic ropes do not subject a climber to such decelleration. Industrial safety experts have looked into the data and elected to choose 6kn as the maximum force a rope should be allowed to impose on the faller. The deformation of the body has thus been quite researched, such as http://www.hse.gov.uk/...df/2003/hsl03-09.pdf
Jesus! Nice and light morning reading. I've seen this before but didn't study it too close. At first glance I didn't see any information on how to factor in a live body. There is the discussion that this is a factor where it talks about a rigid mass (dummy) vs hinged mass (human body). I imagine the data is out there somewhere in any case. If you find it I'd appreciate you directing me to it. I'm a bit swamped right now. swebster, you got it?
I've also seen some other UK study along the same lines but specifically for climbing.
Yeah, the European standard for low stretch ropes and other rope access stuff is 6kN but the test method is dramatically different from the dynamic standard. Perhaps another discussion would be about the logic and value of some of the various standards and not just for rope. I think this topic would eclipse the length of the cordelette threads.:lol:
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swebster
May 12, 2006, 12:11 AM
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Well, that is a lot of information. Unfortunately there doesn't happen to be the answer to the exact question I wanted, but you can get some idea of things from the information on pages 26/27 (number of the document, not the pdf) where they show the extension length for rigid drops/dummies in harnesses. The dummy/harness drop has a much greater extension. This means the force will be less since the energy is absorbed over a greater distance.
These tests also all use load limiting runners (Yates Screamer, Petzl Nitro or similar) which makes it a bit more confusing.
Maybe we should all just tie in with screamers though, that would seem to solve a lot of problems... just make your tie in more bulky. Even ignoring our belay tie in issue though, I sort of wonder why people don't tie in with a screamer when ice climbing etc. then you don't need one for each piece of pro, just one on your harness. (you could still tie in with the rope, then just tie in a bit shorter with the screamer and an alpine butterfly or something).
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jimdavis
May 13, 2006, 1:22 AM
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^^ IMO, I wouldn't use a screamer off my belay loop cause that's one more think to hit me in the balls with every step I take.
Honestly though, the clutter factor on that is a little much. You've already got a ton of clothing, gloves, leashes, maybe 2 ropes into your tie-in points, and a full rack of ice gear on top of that.
Just my thoughts,
Jim
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