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jt512
Dec 12, 2008, 1:46 AM
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adatesman wrote: Jay, Perhaps you could give a link or quick explanation of what you're looking to see for the statistically challenged among us?  -aric.
Say we want to estimate the tension µ in the brake side of a particular rope produced by a particular belay device in the lock-off position in response to dropping a certain weight a certain distance. To do this, we will perform n repetitions of an experiment, and estimate µ as the mean x of the outcomes of the n repetitions. Say we want to be 95% confident that the interval x ± e, where e is our desired margin of error, contains µ. The larger n is the smaller e is, so the question is how big do we have to make n to obtain our desired e.
To answer that question we have to know how precise our individual measurements are; that is, we need an estimate of the random error in our measurements, the standard deviation s. We can estimate s for any given ropebelay-device combination from the experiments that have already been done. Excel has a built-in function for this.
Then, given known s and our desired e,
n = 4s²/e².
When deciding on how big e should be, keep in mind that results for two different belay devices that differ by less than about 2e should not be attributed to a true difference in performance between the belay devices, since the difference would not be distinguishable from one that had occurred by random chance.
Jay
(This post was edited by jt512 on Dec 12, 2008, 4:22 AM)
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JimTitt
Dec 12, 2008, 8:54 AM
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When quoting someone it would be nice if you did it accurately, I wrote"worlds leading climbing equipment laboratory".
They are TÜV Süd in Munich, Germany.
The leader of the Sports Equipment Division of TÜV Süd is Dr Volker Kron who also sits on the various technical commitees of the UIAA as well as CENORM who establish the CE standards and produces recommendations regarding the test protocols.
TÜV Süd have performed several tests on belay devices for the German Alpine Club (DAV) under the leadership of Christian Semmel who is their full-time safety officer and member of the UIAA Safety Commision.
Their test results correspond very closely with other tests performed elsewhere and the general experience of climbers.
Your tests show wildly different results which are not backed up by any of these tests or the experience of users.
It states in the header for this forum In reply to: Feel free to critically analyze and critique in here.
Your test is fundamentally flawed in that belay devices are designed for use in a dynamic situation, to get meaningful results they need to be tested in a way approximating to the real world application.
To test with a load of 31lb in a static situation only tells us how much effort is needed to hold a rucksack up.
To test the feed of a belay plate when it is locked against the karabiner (as shown in your photograph) is meaningless, no-one I know would ever feed this way and the manufacturers did not intend this to be done.
Even a brief look at your results shows how far they are from reality, no one with any experience of, for example, a DMM V-Twin would ever claim it to be three times more powerful than a Reverso³ or 5 times more powerful than a B52 using a 10mm rope.
Nor would anyone possibly believe that a Reverso³ is nearly 10 times more powerful using an 11mm rope instead of an 8mm one.
The issue of publishing a test and purchase recommendations, quote, "The reasoning for this is that new climbers can look at this data an easily determine which devices are optimal for their rope" when completely misrepresenting the performance of equipment is a matter between you and the manufacturers but you can be assured that if an item of equipment from my company was portrayed in this manner you would be hearing from my lawyers.
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jt512
Dec 12, 2008, 4:40 PM
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JimTitt wrote: Your test is fundamentally flawed in that belay devices are designed for use in a dynamic situation, to get meaningful results they need to be tested in a way approximating to the real world application. Even a brief look at your results shows how far they are from reality, no one with any experience of, for example, a DMM V-Twin would ever claim it to be three times more powerful than a Reverso³ or 5 times more powerful than a B52 using a 10mm rope. Nor would anyone possibly believe that a Reverso³ is nearly 10 times more powerful using an 11mm rope instead of an 8mm one.
I agree that we cannot assume that the testing methodology used produces results from which the performance of belay devices in actual field use can be inferred. And lacking evidence of such validity, I think it borders on irresponsible for a commercial outfit to base public recommendations on such test results. Whether or not a manufacturer could win a lawsuit over such misrepresentation of their product, as you suggest, I wouldn't know; but, damn it, Jim, I'm a statistician, not a lawyer.
But, one point: I think you are misinterpreting the results. The friction provided by the belay device should be 31 lb minus the reported results, which with a 10-mm rope would be 30.22, 28.63, 27.06 lb, for the V-twin, Reverso-3, and B52, respectively. Thus the friction produced by the V-twin was only about 1.12 times that of the B52, not 5 times.
Jay
(This post was edited by jt512 on Dec 12, 2008, 4:47 PM)
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ptlong
Dec 12, 2008, 5:16 PM
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jt512 wrote: But, one point: I think [JimTitt is] misinterpreting the results. The friction provided by the belay device should be 31 lb minus the reported results, which with a 10-mm rope would be 30.22, 28.63, 27.06 lb, for the V-twin, Reverso-3, and B52, respectively. Thus the friction produced by the V-twin was only about 1.12 times that of the B52, not 5 times.
Jay, I believe the simple idea is that a belay device acts as a force multiplier, the ratio of the load to the holding force. The test is saying that the force multipliers for the V-twin, Reverso-3, and B52 are 40, 13, 7.9, respectively (for a 10mm rope).
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markanite
Dec 12, 2008, 5:26 PM
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jt512 wrote: I'm a statistician
I would have never guessed that (extreme sarcasm here). Thanks for filling us all in though. I have a computer science (data mining / database background) so I do appreciate the advice.
Any interest in shedding light on how you would develop a "valid" test?
Jim - Please read JT512 post above. I didn't mean to incorrectly quote you. I was just generally interested in what group we are talking about. I'll look for that report.
I believe you'd find the above results to be very similar to "real life". The B52 is noticeably looser than any other device. You can easily feel this: feed a B52 followed by a Jaws. For Trango's credit this is why they have multiple belay devices. Obviously their goal is not to bring out the same device multiple times. The B52's looseness could be an advantage depending on what your doing.
(This post was edited by markanite on Dec 12, 2008, 5:31 PM)
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jt512
Dec 12, 2008, 6:09 PM
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ptlong wrote: jt512 wrote: But, one point: I think [JimTitt is] misinterpreting the results. The friction provided by the belay device should be 31 lb minus the reported results, which with a 10-mm rope would be 30.22, 28.63, 27.06 lb, for the V-twin, Reverso-3, and B52, respectively. Thus the friction produced by the V-twin was only about 1.12 times that of the B52, not 5 times. Jay, I believe the simple idea is that a belay device acts as a force multiplier, the ratio of the load to the holding force. The test is saying that the force multipliers for the V-twin, Reverso-3, and B52 are 40, 13, 7.9, respectively (for a 10mm rope).
OK, I see what Jim is getting at now. In that case I totally agree with him. The results of this test contradict findings from other, far more rigorous ones. So, this test is flat-out invalid, and completely misleading. It would be irresponsible to base product recommendations on this test.
Jay
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jt512
Dec 12, 2008, 6:17 PM
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markanite wrote: jt512 wrote: I'm a statistician Any interest in shedding light on how you would develop a "valid" test?
My honest recommendation is that you are not qualified to conduct these tests yourself. At a minimum you'd need to collaborate with a an engineer with specific, relevant experience.
Here's a pdf by Tom Moyer that summarizes the work done on this question by qualified investigators: http://skywallnet.com/...rver/SAR/S_C_R_B.pdf. Take a look at what has already been done by people who actually know whet they are doing.
Jay
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JimTitt
Dec 12, 2008, 6:30 PM
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In reply to: Jay, I believe the simple idea is that a belay device acts as a force multiplier, the ratio of the load to the holding force. The test is saying that the force multipliers for the V-twin, Reverso-3, and B52 are 40, 13, 7.9, respectively (for a 10mm rope).
Quite so, this is the system used by Black Diamond, Moyer and others. In their tests the devices span a range of ratios from 5 to 10, with the majority around the 7 mark. From other drop tests we know that the only device available at the moment that gets higher than this is the GriGri at 20.
The results for the B52 show just how wrong the test results are, Trango“s own test results against the ATC show an increased braking force of 16% whereas the results published here show a decrease of 53%.
jt512 wrote.: In reply to: I agree that we cannot assume that the testing methodology used produces results from which the performance of belay devices in actual field use can be inferred. And lacking evidence of such validity, I think it borders on irresponsible for a commercial outfit to base public recommendations on such test results.
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ptlong
Dec 12, 2008, 6:49 PM
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jt512 wrote: OK, I see what Jim is getting at now. In that case I totally agree with him. The results of this test contradict findings from other, far more rigorous ones.
Results from Black Diamond are available in the following PDF by Tom Moyer (the same paper Jay just posted):
http://www.xmission.com/...nd_Rescue_Belays.pdf
One interesting chart is on page 35 of the document (page 36 of the pdf). It compares the force multiplier for different hand-side holding forces for about a dozen devices. It's clear that in some cases a low hand-side force translates into a much higher multiplier. Many of the hand-side forces in Mark's test were low, on the order of one pound, where BD found that some devices had multipliers that were unrealistic.
Mark stated that he tested other weights and found that 30 lbs (load side) was sufficient for obtaining "proportional results". It would be interesting to see the raw data.
(This post was edited by ptlong on Dec 12, 2008, 6:54 PM)
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maldaly
Dec 12, 2008, 6:58 PM
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Mark,
Great work on all these tests. Unbelievably, the CE or the UIAA still hasn't come up with a standardized test for belay devices. They keep arguing about it but can't come to a consensus for a meaningful and fair test. For a category that is so mission critical (If it fails there is no backup, unlike the usual situation with a carabiner or cam.) this is appalling.
So we made up our own test when we were developing the B-52. It's described in detail here: http://www.trango.com/cat.php?t=B.
There are 2 main differences between our tests. First, we used a live body as the weight. There are differences in how a belay device works under high loads and low loads as evidenced by the differences we recorded in the B52 test. A side benefit is that we didn't have to haul the load up each time. The crash test dummy just climbed back up. Second, we allowed the belay device to free-locate between the load and the anchor resulting in what you would call a -90° angle. Granted, the angles chosen are somewhat arbitrary. We chose ours based on observations of what happens when a belayer catches a hard lead fall. Their body is twisted to the side and the lock-off hand is aligned directly opposite the direction of the load. For lower load catches (TR falls or whatever) your 55° angle may be more accurate however we felt it more important to measure relative forces at what would be the severe loads of a lead fall.
The numbers we arrived at are relative. They will vary with the weight of the climber while staying the same relative to each other. I think that's what's important. We used range of weights, from 120lbs to 190lbs and the relative performance didn't change much.
Again, like you, we choose to keep the test fairly narrow. We used new ropes and conducted all the tests on the same day so humidity and temperature didn't effect the outcome. Had we decided to test all permutations, from diameter of ropes to age, stiffness and whatever else, we'd still be testing 10 years later.
Two more points of observation. First, I don't think that climbers care too much about weight in this category. The difference between the heaviest and lightest in your test is less than an old carabiner. It just confuses things. I think.
Second, the comments I get most frequently about belay devices are in regards to how well they feed. "I love that thing! It feeds so smooth" is heard way more often than, "Man, that thing locks off great." I'm not sure your test captures the feed-ability well. For me, the way a device feeds has a lot more to do with its propensity (or lack thereof) to lock up suddenly when you're feeding than it does with how easy it is to drag rope through it when you blow it.
REI had a good test they were doing back in the day. With the convenience of plotted load cells, a UIAA drop tower, a warehouse full of ropes and belay devices, and an on-staff engineer, they were able to perform a test we can only dream of. Basically, they set up a UIAA drop test using a 40kG weight. Rather than anchor the rope they threaded it though a clutch which was calibrated to slip at 25 lbF, approximately the amount a surprised beginner can hold in the brake position. They cut loose the weight and measured how much rope slipped through the clutch. Pretty cool test and it mirrored out results almost perfectly.
Well, keep thinking. Any data we can get on belay devices is good.
Climb safe,
Mal
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adatesman
Dec 12, 2008, 8:54 PM
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maldaly
Dec 12, 2008, 10:20 PM
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I think REIs clutch was more ghetto that that. They used two metal plates held together with 4 bolts at the corners. The plates were held apart by compression springs or an elastomer. The rope was placed in between the plates then the bolts adjusted until it took 25 lbF to pull the rope through. Care had to be taken to ensure that the rope would run fair because any kink or blip would alter the results.
Mal
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JimTitt
Dec 12, 2008, 10:29 PM
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The DAV/TÜV set-up was a fixed roller and rotating roller mounted between two plates and with the rotating roller sliding on a yoke. this was forced onto the fixed roller by a wingnut and bolt.
They used a factor0.4 fall with an 80kg weight and 250N braking force. Brake force angle to rope was 137°.
They also tested with 100N and 400N braking force to see the relationship.
I“ll dig out a few links tommorow and post them, it“s 11.30 at night here.
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adatesman
Dec 12, 2008, 10:34 PM
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maldaly
Dec 12, 2008, 11:05 PM
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I suppose there are a lot of ways to skin that cat. The key is to get something which has no startup inertia (not sure that's the right word) which would allow the force to ease off after the initial slip. The fly fishermen call it "sticktion" when talking about the drag on fly reels. Cheaper reels stick for a moment, then allow an even pull off the spool.
Mal
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adatesman
Dec 13, 2008, 12:45 AM
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maldaly
Dec 13, 2008, 5:08 AM
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The high end reels all have some sort of disc mechanism. Abel, one of the most highly regarded reels, uses a cork disc, Lamson uses a conical polymer and Galvan uses a graphite disc. They all work well but are all expensive ($400-$800) units. Not sure the ghetto rig wouldn't work as well. We don't have to pretty, lightweight or mass-produce-able. Just cheap.
Mal
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rgold
Dec 13, 2008, 6:03 AM
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Mal, I'd like to see your tests, but I'm not getting anything when I try the link you posted. Is it ok?
Two comments about the dynamic tests.
1. I think you mean an 80 kg weight, not 40 kg.
2. According to the extensive studies done by the CMT section of the Italian Alpine Club, the peak load to the anchor occurs during what they call the "inertial" phase of the belay, in which the belayer's arm is pulled toward the belay device with no rope slipping through the hand. The inertial phase ends when rope starts to slip through the hand, in many cases because the hand has run into the belay device.
Building a test system with a clutch to model the hand cuts out the inertial phase during which the peak load occurs, so it would seem that such tests will underestimate the loads to the belay chain and overestimate how much rope will slip through the belayer's hand.
Edited to try to get rid of strange formatting,
(This post was edited by rgold on Dec 13, 2008, 4:14 PM)
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maldaly
Dec 13, 2008, 3:38 PM
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RGold,
No, 40kG was the mass they used. Not sure what the thinking was but I would guess that they couldn't stop an 80kG mass in the distance of their drop tower.
Adatesman, the sticktion I refer to in a fly reel happens without having to overcome inertia. When you slowly try to rotate the spool of a bad reel (on a fly reel with a real drag system) you can feel them "stick" for a moment before they begin to rotate.
When you click the link to our results it should download a pdf file. Whether or not it opens depends on your settings.
Mal
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rgold
Dec 13, 2008, 4:17 PM
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So, Markanite, you asked for feedback. Here's what you got:
1. The values you got are, in a number of cases, wildly out of line with other tests by manufacturers and labs.
2. Your data has not been given appropriate statistical treatment.
3. Your indices conflate unrelated parameters and may be generating spurious relationships.
My own take is that, however well-intentioned, this data is not informative and does not help the climbing community understand or evaluate the performance of the devices in question. I might add that the presentation is confusing and the choices made in that presentation difficult to fathom. Personally, I would never cite these results in any discussion I participated in about belay devices, and I would advise anyone who did cite this data to look elsewhere for more meaningful results.
I'm not trying to be mean, just matter-of-fact. I assume you genuinely wanted some kind of evaluation and weren't just trying to generate traffic for your business, and I think the verdict is in. The tests need to be redone and the statistical treatment needs to be upgraded. (Here you got free advice that would otherwise have cost you quite a bit, I think.)
Finally, a comment about the huge discepancies in some of the data. It is far more useful to describe the performance of a belay device in relative terms as a force multiplier rather than in absolute terms of how much force needed to hold a specific load. But such descriptions are only useful if they are true, meaning in this case that the belay force is always a constant fraction of the load held. I don't know if this is an experimental fact or just a plausible but untested assumption. Perhaps it is more or less true for a range of loads, but begins to show non-linear behavior for very small and very big loads---such phenomena are typical of rope response curves too.
So, part of the discrepancy you are seeing in your data may be because you are using loads that are too small and so are outside the approximately linear part of the device's braking behavior. The idea of testing the devices with a load one-third the minimum the device would be expected to hold in the field seems an extremely poor choice to start with, and it may be part of the reason some of your data bears no relation to presumably more reliable results.
So now the big question: what are you going to do with this feedback you asked for? Will you leave such flawed data up for the climbing public to consume under the doctrine of caveat emptor? I suggest that you take it down and redo the tests, or at the very least add a caution saying that substantial concerns have been raised about the data and its analysis and provide a link to the discussion here.
----------------------------------------------------
P.S. Mal, your link doesn't work at all for me. I get a blank Trango page with no content. Could this be yet another in the endless list of IE issues? The link to your site supplied by adatesman, http://www.trango.com/pdfs/BelayDeviceTests.pdf, works just fine.
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ptlong
Dec 13, 2008, 4:45 PM
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rgold wrote: P.S. Mal, your link doesn't work at all for me. I get a blank Trango page with no content. Could this be yet another in the endless list of IE issues? The link to your site supplied by adatesman, http://www.trango.com/pdfs/BelayDeviceTests.pdf, works just fine.
Instead of
http://www.trango.com/cat.php?t=B.
try
http://www.trango.com/cat.php?t=B
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brenta
Dec 13, 2008, 6:24 PM
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adatesman wrote: Any idea how they solve this issue in fly reels? The only one I ever had was a Kmart special and rather clicky in its action. Its an interesting issue, since it means either finding a friction material with equal static and dynamic friction coefficients or a mechanical way to compensate for the difference.
Regarding belay device testing, here are a couple of references to papers by a group including people from Petzl:
@INPROCEEDINGS { Manin05 ,
AUTHOR = "L. Manin and J. Mahfoudh and M. Richard and D. Jauffres" ,
TITLE = "Modeling the climber fall arrest dynamics" ,
BOOKTITLE = "ASME International Design Engineering Technical Conferences and Information in Engineering Confeence, IDETC-IEC 2005" ,
ADDRESS = "Long Beach, CA" ,
MONTH = sep ,
PAGES = "1077-1084",
YEAR = "2005"
}
@INCOLLECTION { Manin06 ,
AUTHOR = "L. Manin and M. Richard and J.-D. Brabant and M. Bissuel" ,
TITLE = "Rock Climbing Belay Device Analysis, Experiments and Modeling" ,
BOOKTITLE = "The Engineering of Sport 6" ,
EDITOR = "S. Haake and E. Moritz" ,
PUBLISHER = "Springer" ,
VOLUME = "1" ,
PAGES = "69-74" ,
YEAR = "2006"
}
Only the second is specifically about belay devices, but the first briefly mentions that "To reproduce the behavior of the belayer hand on the rope, a false hand was realized using two steel plates clamped by screws and pressed on the rope by the springs. The deflection of the springs in measured so that the pressure force on the rope can be determined."
The second paper uses a different "false hand." In short, a spool of rope is connected through a torque meter to an adjustable torque limiter set to slip as soon as the tension in the rope exceeds 160 N. (I'm going from memory. The 160 N may be inaccurate.)
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rgold
Dec 13, 2008, 7:19 PM
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ptlong wrote: rgold wrote: P.S. Mal, your link doesn't work at all for me. I get a blank Trango page with no content. Could this be yet another in the endless list of IE issues? The link to your site supplied by adatesman, http://www.trango.com/pdfs/BelayDeviceTests.pdf, works just fine. Instead of http://www.trango.com/cat.php?t=B. try http://www.trango.com/cat.php?t=B
Oopsie, my bad. Sorry about that Mal. Thanks ptlong.
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JimTitt
Dec 13, 2008, 8:23 PM
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A few years ago I looked into this a bit, the textile industry have the problem of starting and stopping the bobbins at very high speeds and the jerking in the transition from static to moving friction causes a lot breakage. The reason they clad beautiful legs in nylon is because the two coefficients are virtually the same and so they can weave with much finer thread. mu is about 0.3.
For us this shouldn“t matter anyway as in real life the rope is also transitioning between static and dynamic at the moment of impact just like it would on a test rig. If there was any effect at all it would show up on the load cell trace.
One problem if one decided to mathematically model a belay device instead of practical testing is that the coefficient of friction of polymers changes considerably under load which certainly complicates things a lot.
The inertia problem of the arm/hand is going to be difficult, personally I would just go for a comparison test anyway.
Which gets us to MALDALY“s comment. In reply to: Unbelievably, the CE or the UIAA still hasn't come up with a standardized test for belay devices. They keep arguing about it but can't come to a consensus for a meaningful and fair test. For a category that is so mission critical (If it fails there is no backup, unlike the usual situation with a carabiner or cam.) this is appalling.
I spent an evening with someone intimately involved for many years in this commitee and learnt many interesting things. "Like searching for the Holy Grail but takes longer and with less chance of success" was his embittered resume.
The first problem is IF there is a dynamic test then what rope? Ropes change all the time, and of course there would be nothing stopping a major manufacturer running off his own special test rope, getting a CE cert and obrtaining some stunning test numbers
So we need a UIAA spec, certified test rope.To agree on a spec and get a supplier to guarantee supply in the future will take years if it can ever achieved.
And then what test? As Mal says, these things are vital so probably they come under the UIAA“s beloved "safety chain". No problem, it must hold the worst case fall, 12kN impact (max allowed rope) with a normal climbing rope- say 60m, in a factor two fall. If the belayer is to survive this uninjured then there is only one device as yet tested that could (probably) do this, the GriGri.
No national federation is ever going to ratify a standard excluding every other device but the GriGri and anyway who is going to pay for this 180+m test tower?
So a compromise has to be made, how about using a 2m drop tower? Well, yes but if it“s going to be a full UIAA drop with 80kg we are back again to the GriGri.
Some commitee members resign as the safety chain has been ignored.
Okay, another compromise, reduce the fall factor to something that most devices can hold. without considering what really can occur.
At this point more members resign, saying it appears they are no longer writing a standard.
The Mountain Guides raise their heads and point out that the rope once round a rock spike, tree, metal summit cross or whatever is better anyway and they will never agree to carrying and having to use some metal rubbish.
The commitee waits until the guides leave the UIAA to form the UIGM and deliberates further.
The UIAA sharp edge test disaster occurs, heads roll and the technical commitee is told to get it“s act together.
The UIAA faces a financial crisis as two major national federations announce they are leaving.
UIAA hires an agency to assist in marketing their "safety label".
UIAA announces the belay device standard is soon to be issued.
Is there a connection here?
After nearly two decades of deliberation it will be interesting to see just how many compromises (with our safety) they have made.
Cenorm will have even more problems as they have to write proper internationally acceptable standards which may have to stand up to judicial scrutiny so don“t hold your breath on this one either.
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markanite
Dec 13, 2008, 10:36 PM
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I'm actually on a climbing trip right now (using my cell for wifi) so excuse the extremely short response. The only response that I don't agree with is people who believe that we shouldn't test gear or that climbing gear is so incredibly complex that it is untestable. I'm fine with people telling me why my test is problematic or straight out wrong. Obviously there are financial problems involved and realistic standards need to be developed (it isn't realistic to do a multi-million dollar test in a niche market).
I'm not arguing my tests are the leading authority by any means, but I'd hope that they would inspire others to go back to the drawing board and design their own tests. The climbing community is one of the most intelligent communities, so why aren't we developing our own standards as opposed to just telling everyone it's impossible? As Mal said: Any data we can get on belay devices is good.
I do have all the belay devices (all in perfect condition). I'd be willing to lend them to any reputable organization or university who would be interested in testing the gear. In exchange I'd recommend they release their report under the GNU free documentation license. Though this only subsidizes a small portion of the test's cost maybe it would inspire others.
(This post was edited by markanite on Dec 13, 2008, 10:40 PM)
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