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tenn_dawg
Jul 24, 2003, 1:09 AM
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Dan,
That study is good stuff. Finally, an experiment that measures forces at the lead placement. I haven't got to read the full text yet, (economics test tomorrow) but I'll get on it as soon as I get a chance.
Thanks for digging up a good study!
Travis
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alpnclmbr1
Jul 24, 2003, 4:03 AM
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Tenn-dawg,
It is pretty good stuff. Kind of funny that the testing machine company was the one to post it.
Good luck on your test.
d.
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traddad
Jul 24, 2003, 2:58 PM
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One improvement I'd like to see on that test is to simulate the belayer. I didn't read the whole test (I'm at work) but I suspect the 'biner hooked into the belay device is attached to a post or some other completely static set up. Like I said in an earlier post, the acceleration of the belayer, friction in the harness, compression of the kidneys and nuts (assuming a male climber) :D may take at least some of the edge off the impact force. What I'd REALLY like to see is a "Real World" test scenario where a trained belayer catches a large number of falls (say, 50+ for each device) and the impact force is averaged over the large N for each device. While the error bars would probably be huge, statistical methods could be used to test if the mean was representative.
I'm an ecologist working in the field of ecotoxicology. I hate it when people try to extrapolate from laboratory derived data to characterize the real world. The complexities involved in real world situations often (read: most of the time) drown out what ever variable was being tested for in the lab. There is a LOT of noise out there.
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tenn_dawg
Jul 24, 2003, 3:07 PM
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Very good points, I still can't read the entire test, but I think the resuts may be slightly suspect. When I get a chance I"ll really pool over the results, and methods and figure out exactly what they've shown.
You can only take experiments results so far. It is still nessessary to question results and formulate your own conclusions.
Travis
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sspssp
Jul 24, 2003, 3:24 PM
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[quote=]The test findings confirmed what experienced climbers had suspected but never had actual load values to prove. For example, the cam lock static belay device put the greatest load on the protection--2215 pounds. The load on the belayer in this test was 839 pounds and the load on the climber was 1382 pounds. Another type of belay device called the Trango Pyramid was expected to have a light catch. It did, expelling nearly 30 inches of a 10.5 mm rope.
I am back to thinking grigri's are bad for trad.
First, as the other poster pointed out, you aren't going to get 839 pounds of force on the belayer, unless the belayer is anchored without slack, which most are not. Instead, you are going to pick the belayer up off the ground and get at most a few hundred.
Second, this is a pretty extreme fall scenerio. Not one that comes up that much.
Third, the ATC type device let 30 inches of rope go through the device while the brake force was being applied. So how many of you wear gloves when belaying? What type of rope burn do you think you are going to get after 2 and half feet of rope slice through your hand? Now that your belayer's brake hand is a raw, bloody mess, are they going to be able to keep the rope locked off? Maybe, but there are up sides to the grigri.
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jt512
Jul 24, 2003, 4:23 PM
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In reply to: That's quite a difference, around double the force on the protection from a static Gri-gri belay (or Muntner?). Reinforces my own prejudice that for trad free climbs, at least, ATCs and the like are the best way to go. The other striking thing in this thread is the note about carabiners breaking, but not the rope which was theoretically weaker. There has been much discussion on these forums about the strength of various knots in rope and webbing, but I can't offhand recall reports of accidents where ropes or slings broke (cut or came untied, yes). On the other hand I've broken two carabiners in falls myself, and heard of many others. It seems like the metal gear in the system often might be more fragile, in practice, than its rated strength would suggest.
No, it's not that. When biners break it is because they have been loaded improperly, most often (I suspect) with the gate open. The worst CEN biner will hold the worst-case lead fall if loaded along its major axis with its gate closed. On the other hand, open-gate strengths of biners range from 7 to 10 kN (1600 to 2300 lbf). Ovals, IIRC, are permitted to be even weaker. One glance at the paper posted by Alpnclmbr1 should convince you to invest the extra $3/biner for the better, higher open-gate strength biners, such as Petzl Spirits or DMM Wirelocks.
-Jay
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jt512
Jul 24, 2003, 4:37 PM
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In reply to: One improvement I'd like to see on that test is to simulate the belayer. I didn't read the whole test (I'm at work) but I suspect the 'biner hooked into the belay device is attached to a post or some other completely static set up. Like I said in an earlier post, the acceleration of the belayer, friction in the harness, compression of the kidneys and nuts (assuming a male climber) :D may take at least some of the edge off the impact force.
While those factors reduce the impact forces of actual falls, the test results are not necessarily unrealistically high. In most real-world falls the impact forces on the anchor and the falling climber are increased by frictional forces between the rope and intermediate protection. These not only act as additional braking forces, but they also reduce the amount rope stretch, effectively increasing the fall factor.
Evidence that real-world impact forces are at least on the order of those reported in the test come from reports of biners breaking in falls. Presumably, these biners are loaded improperly, usually gate open, and so will fail at loads ranging from 1600 to 2300 lbf. Biners have been failing prior to the invention of the grigri, which suggests that real-world impact forces can exceed those reported in the test.
-Jay
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alpnclmbr1
Jul 24, 2003, 5:04 PM
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Thanks Jay,
For one, the harness and knots do not absorb a lot of energy in the system according to the authorities I have read. (clyde soles among others) As far as lifting the belayer, that would happen with a grigri or atc.
For two, these are worst case falls, which are the ones you are most worried about. The fact that they do not happen very often is irrelevant, and you can extrapolate from the data offered.
For three, when speaking in terms of fall factor calculations more commonly found in actual climbing, the forces are actually worse then the numbers would suggest. This is due to friction in the system from the rock, biners etc. that limit the absorption ability of the rope by focusing the force on the section of rope between you and the last piece. (thus the wear pattern observed on sport climbing ropes)
For four, I notice a pattern of analyzing the data to suit your own preconceived notions. The test was set up by trained engineers who took as many worthwhile factors into consideration as they could. (and from inferences in the article they probably tested the issues your speaking of)
It is a fact that in a close to factor 2 fall scenario a grigri could contribute to blowing out your anchor system. And none of your comments on how the test could be improved would effect the test results in this regard.
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papounet
Jul 24, 2003, 5:24 PM
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dear
There is nothing better than data recorded in scientific experiment to contradict "beliefs".
If you think that a belay system anchorer to a live body is always better than a device anchored to the rock, read on.
Real test data available from http://journal.uiaa.ch/archive.asp
the file you want is http://journal.uiaa.ch/download/20003.pdf
...
During 1998 and 1999, a few hundred
tests were conducted on rock and
on the Tower, comparing belay devices
and belay systems, use of single rope
and twin ropes, rock-belay and bodybelay.
here in order to stimulate discussion.
...
During 1999, two experimental sessions
were held at Passo Rolle (Dolomites
region). A rock face was
equipped with runners up to a height of
12 meters (Fig. 1). An 80-kg steel mass
was raised 2 m from the last runner
above an overhang, thus providing a
4-m free fall.
Peak forces and, more recently, full
plots of the forces occurring in two or
three points of the belay chain were recorded.
In the two sessions, about 100
cases were studied.
...
the part I prefer
========
The inertia of the belayer’s body can lead to a
higher peak load on the last runner,
compared to the load caused by the regular slippage of the
rope in a device attached to the stance. The role of the inertia is
tricky; e. g. it is not always true that the load on the
last runner is lower when the friction along the
runner’s chain is lower: the pull on the belayer’s
body is stronger in this case, so that his inertia can be the prevailing
effect in determining the forces on the last runner. Depending
on the circumstances, an increase in the belayer’s mass
can lead to a reduction or an increase of the load on the last runner
or on the stance.
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micahmcguire
Jul 24, 2003, 8:21 PM
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i don't like to use my grigri except for belaying my follower after I have led up a climb. Its a very convienent bit of gear to have, especially when room on the belay platform is limited, if you have to be periodically fiddling with things with one hand, etc. Aside from that, its bulky, its big, and people don't seem to know how to use it properly. My two cents boils down to this: if someone gives you a grigri for your birthday or what-have-you, yippee. If not, its way too pricey and bluky to be worth spending $$$ on. Get a cheap ATC, its smaller, lighter, and does the same job.
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mewalrus
Jul 24, 2003, 10:45 PM
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In reply to: First, as the other poster pointed out, you aren't going to get 839 pounds of force on the belayer, unless the belayer is anchored without slack, which most are not. Instead, you are going to pick the belayer up off the ground and get at most a few hundred.
Please explain how a 176 pound weight generates over 2,000 pounds of force at the protection? how?
I believe you could easily generate 839 pounds of force on a 150lb belayer. Plus the force at the belayer is not the significant number anyways, its the force on the protection thats significant.
pounds force=(32.174 * pounds mass * ft)/ seconds^2
The belayers weight is not very significant. The TIME scale is what very signifcant. You see that time squared. If you double the time it takes to stop the fall the force goes down by a factor of 4. If you triple the time the force goes down by a factor of 9!!!
Anything you can do to lengthen the time will have the greatest reduction in force. This is how dynamic ropes work, you fall further but the force is way less because they stretch out the time factor.
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traddad
Jul 24, 2003, 10:47 PM
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Papounet,
What I think they are actually saying is that friction caused by the rope running through the runners actually decreased the load placed on the top runner. I whole heartedly agree with this. Another reason to sew up a pitch like Betsy Ross :D. It does not mean, however, that accelerating the belayer is a bad thing. It just means that the runners act as "shock absorbers" if you will isolating the belayer from the falling object. Think of it as the difference between having someone fall with a lot of slack on a top rope vs falling with the same slack with the added drag of the runners between the belayer and the climber.
The less rope drag you have the more force you'll put on your top runner?!
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alpnclmbr1
Jul 24, 2003, 11:53 PM
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In reply to: Papounet, What I think they are actually saying is that friction caused by the rope running through the runners actually decreased the load placed on the top runner. I whole heartedly agree with this.
This is completely wrong, the friction on the lower pieces increases the impact forces on the last piece and the falling climber by making the rope between the climber and the last piece of gear absorb more of the force, not less.
To put this another way, If you only had one piece in, the rope between the top piece and the belayer would all stretch equally. Each point of friction prevents that force from spreading over the whole length of rope equally, leading to a higher impact force due to making less use of the ropes ability to absorb energy. This is why real world fall forces are worse then the numbers only calculations.
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micahmcguire
Jul 25, 2003, 1:23 AM
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agrees (finally) with mewalrus. its decelaration over time that prevents damage to you, to your anchor, to everything. the more time it takes to slow down, the less of a shock it will be on the anchor, the rope, the climber, their poor crotch, etc. This is why airbags are in cars. It takes longer to deccelarate through an airbag than into a steering wheel, and certainly does less damage to the occupant.
also I should point out that alpineclimber1 (SP) is quite correct. very correct. do not question.
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traddad
Jul 25, 2003, 1:41 AM
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Hmm...I see your point. Having less friction in the system will let the rope do the work it's designed for. Makes sense. I retract my previous statement. Guess I was thinking static rope thoughts.
Shall I run it out, sir?
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alpnclmbr1
Jul 25, 2003, 1:48 AM
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In reply to: also I should point out that alpineclimber1 (SP) is quite correct. very correct. do not question.
Actually, I wish you would challenge my assumptions, if I am wrong, I want to know it. The whole point of spending time on this site is to learn a thing or two.
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micahmcguire
Jul 25, 2003, 2:01 AM
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ok, but I won't, because you are right. obviously a twenty foot chunk of rope won't stretch as much as a 100 foot chunk of rope of the same type. elemetary my dear alpnclmbr1. or were you talking to everyone else?
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norushnomore
Jul 25, 2003, 9:55 AM
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Look into using TRE.
Will lockup like gri-gri but will let rope slip like an ATC.
Best of both and you double-rope rappel with it (with no need for the back up either)
G
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papounet
Jul 25, 2003, 1:10 PM
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My previous post was a bit rushed and I may have cut&pasted a passage which wasn't the most relevant.
I would encourage you to read carefully the UIAA document.
you'll find such gems as :
" At the beginning, we had to devote most of our efforts to convincing the
climbers that in the large majority of real cases the friction between rope and
rock is determinant in holding the falling climber; consequently, testing belay
at the tower was essential to appreciate what can really happen in a bad
(though unlikely) case, i. e. when there is no friction. "
or
"In the body-belay process the first phase is “inertial, ...".
Doing some more searches I found the one of most complete scientific document
yet from the Central Commission for Equipment and Techniques of the Italian Alpine Club
http://www.caimateriali.org/Articoli/TecnicheDiAss_/tecnichediass_.html
http://www.caimateriali.org/Articoli/articoli.html
But as my italian is not up to par, I'll pass on this article
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papounet
Jul 25, 2003, 1:47 PM
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Google is magnificent: http://www.leeds.ac.uk/sports_science/abstracts/climb99/wnachbauer1.htm
1st INTERNATIONAL CONFERENCE ON SCIENCE AND TECHNOLOGY IN CLIMBING AND MOUNTAINEERING.
7th - 9th April 1999 University of Leeds, UK.
--------------------------------------------------------------------------------
Forces on the Falling Climber Depending on Different Belaying Techniques
R Messner, G Meraner, T Schliernzauer, B Knuenz, W Nachbauer
Department of Sport Science, University of Innsbruck, Austria
Traumatic and overuse injuries to the spine were observed with climbers falling in the rope. The purpose of this study was to investigate the influence of different belaying behaviours and devices on the force measured between rope and harness of a falling climber.
One subject (m = 70 kg) performed standardised falls with a fall factor of z = 0.375. The following situations were tested: static belay at a bolt (1 trail), static belay at the body using a Grigri (1 trial), belay with backward movement of the belayer using a Grigri (1 trial), dynamic belay by a jump using a Grigri (10 trials), dynamic belay using a figure of eight (10 trials), dynamic belay using a HMS-karabiner (10 trials). The force between rope and seat harness was measured by a strain gauge. From the recorded force curves the peak force was determined and compared for the different situations.
For the single static belay at a bolt an about two times higher peak force (4006 N) than the mean peak force of the 10 dynamic trials using the Grigri occurred (2083 N, s = 175.7 N). The differences between different belaying behaviours using the Grigri were as follows: in case of a backward movement of the belayer the peak force was 3887 N which is close to the static trial, in case of no movement of the belayer the peak force was 3267 N, and with a jump of the belayer in rope direction it was 2083 N. The comparison of the belaying devices showed mean peak forces of 2368 N (s = 172.5 N) for the HMS-karabiner, 2197 N (s = 234.0 N) for the figure of eight, and 2083 N (s = 175.7 N) for the Grigri. The difference between HMS-karabiner and Grigri is statistically significant.
=====
My take:
doing a jump with a Grigri, despite not letting go of the rope, allow a smoother fall arrest, with less force on top piece and on climber arrested.
If the fall was uncertain, one step forward would be quite beneficial
if the fall was clearly dangerous, extreme measure such as running gbackward to limit fall length could be adequate despite harder fall arrest.
===
The post to end all post ????, not yet
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tradklime
Jul 25, 2003, 5:24 PM
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In reply to: My take: doing a jump with a Grigri, despite not letting go of the rope, allow a smoother fall arrest, with less force on top piece and on climber arrested.
Now apply that to the context of this thread, trad climbing. A step further, to a hanging John Long style belay. How much jumping are you going to do? I think the best context to look at it is that the belayer will be somewhat static in position. Having a device that allows some rope slip will provide the next best thing to a jump with a static device.
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micahmcguire
Jul 25, 2003, 5:28 PM
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very much agreed
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brutusofwyde
Jul 25, 2003, 9:13 PM
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In reply to: Too heavy and bulky?????? gimme a break i just went on REI's home page where they list a BD ATC (not XP) as weighing 49 grams and a gri-gri weighing 225 grams Bottom line: A gri-gri is only 176 grams heavier than an ATC.
Another way of looking at this is the grigri weighs more than FOUR TIMES what an ATC weighs, and is not an effective rappel device. And the ATC is not the lightest belay device on the market.
I try to pare every gram, and maximize utility of what I carry.
60 carabiners @ 65 grams apiece vs 60 Neutrinos at 37 grams each.
Titanium cams and DMM cams vs. Camalots can make pounds of difference in a double set of cams.
8.1mm double ropes where full rope rappels are necessary.
a stove that weighs 64 grams.
In reply to: I'm not trying to sway anybody's opinion, I'm just trying to thow out the arguments that's it's too heavy and bulky.
I'm not convinced, and I own two Grigris. Hard backcountry climbs with long approaches require some significant weight management.
Brutus
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jt512
Jul 25, 2003, 9:19 PM
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In reply to: In reply to: Too heavy and bulky?????? gimme a break i just went on REI's home page where they list a BD ATC (not XP) as weighing 49 grams and a gri-gri weighing 225 grams Bottom line: A gri-gri is only 176 grams heavier than an ATC. Another way of looking at this is the grigri weighs more than FOUR TIMES what an ATC weighs, and is not an effective rappel device. And the ATC is not the lightest belay device on the market. I try to pare every gram, and maximize utility of what I carry. 60 carabiners @ 65 grams apiece vs 60 Neutrinos at 37 grams each. Titanium cams and DMM cams vs. Camalots can make pounds of difference in a double set of cams. 8.1mm double ropes where full rope rappels are necessary. a stove that weighs 64 grams.
Brutus, tell me you had to look up those weights, and that you don't have them all memorized.
-Jay
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