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When to use screamers
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By rgold
From Poughkeepsie, NY
Nov 21, 2012
The traverse out to the Yellow Ridge on the Dogstick Ridge link-up.  Photo by Myriam Bouchard

I found the link to the CAI tests: www.caimateriali.org/index.php?id=27 You'll have to read Italian or struggle through the results of Google Translator. Here is the translation of their summary of the tests of screamer-type load limiters:



1. Commercial shock-absorber

...But - of most interest to climbers - the lack of utility for the purpose of reducing the load on the last anchor point was also confirmed, as is clear from the results of dynamic tests. In all test conditions, in fact, the presence of the shock-absorber was practically irrelevant, in the sense that the reduction of the load on the anchor was almost always insignificant or at most - under high loads (approx. 800 kp) and mild activation of the belay device - very low.

In the light of its poor ability to absorb energy, it is considered that this tool can be of some utility only when the overall energy involved is relatively low, ie in case of drop heights of a few meters (eg a fall from 1 m above the top piece).



So in more practical terms, the screamer may be of some use until the pro is below your feet, after which its contribution to load reduction is negligible. Perhaps I'll post more about what the tests say, including the observation of an increase in anchor load, but I must attend to some other things first.

A happy Thanksgiving to all, whether you believe in screamers or not.


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By bearbreeder
Nov 21, 2012

once again ... MP is a great place for telling other people how to climb their own climbs ;)

god i luuuv the intrawebs ...

dont use PAS, dyneema, evolve defies, ATC guides, gri gris, screamers etc ...

in real life people just go out and use what they want ... =P


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By divnamite
From New York, NY
Nov 21, 2012

Dana wrote:
Check the definition of evidence.

Sorry, can't do homework for you.


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By divnamite
From New York, NY
Nov 21, 2012

bearbreeder wrote:
once again ... MP is a great place for telling other people how to climb their own climbs ;) god i luuuv the intrawebs ... dont use PAS, dyneema, evolve defies, ATC guides, gri gris, screamers etc ... in real life people just go out and use what they want ... =P

Best post so far!


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By patto
Nov 21, 2012

Those figures are pretty damning of the performance of screamers. But unfortunately it seems people are here to argue their opinions rather than discussing the truth.


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By Larry S
Nov 21, 2012
The wife and I road-trippin on the Connie.

I know this is beaten to death on here and i'm just going to stoke the fire for more argument/nasty responses, but i have been pondering the math of and decided to write up little essay anyways, it might be of value to someone. If it's not for you, ignore and carry on... so here's a little physis i scribbled on my notepad. It's probably close. There are alot of assumptions.

Assuming a 2.4kn activation force (550 lbs), and an extension of 30cm (~12"), and assuming the the deployment is not in discrete steps as the stitches tear, fully deploying a screamer should take ~734 Joules of energy (2446N * .3m)

Now, we can figure out how high a mass must be to have a potential energy capable of generating that much energy U= m(mass) * g(acceleration by gravity) * h(height). Assuming a mass of 80kg (~175lbs), we find a fall of .93 meters has that much energy. That's almost exactly 3 feet. Now, this imagined scenario is a perfectly system, nothing is considered aside from the perfectly static anchor, the screamer, and the falling mass. Nothing extends or shifts to spread the energy over a longer duration of time/distance other than the screamer. Think of a steel mass falling onto a dynema daisy or steel cable connected to a bolt with a screamer in between. (note that this is 3' from the time the fall starts to the time the fall is completely arrested, w/ the screamer deployed - it's really a 2' fall onto the screamer + elongation of the screamer)

This is probably why they say that the screamer effectively shortens a fall length (as seen as force on the anchor) by 3', it absorbs the energy of a 3' static fall. Any falls greater than this have more energy, and when we add in the dynamics of a belay, dynamic rope, etc, it's a very complicated system with interactions between the different parts. It's quite probable that having the screamer in the system affects the dynamics of how the rope/belay work with longer falls, so it's hard to say how effective they are. For short falls, they definitely have potential to limit the load. For longer falls, they dissapate some of the energy early on, but we don't know what happens after it's fully deployed. From the Yates and BD data, they look to help, though the BD data shows not as much as Yates claims. The yates data doesn't really tell us anything about how they tested it, and the BD tests have a static belay and don't show any long/low FF falls.

If we really wanted to see how this works, we'd need to get a setup like user "20kn" had for seeing the loads generated in bounce testing and about a dozen screamers, and plot out the load as a function of time for different fall lengths with different fall factors for systems with and without screamers and analyze them.

Also want to point out to the "useless in realistic/long falls" crowd that Yates does make screamers called "zippers" with double the extension/stitching to tear that are meant specifically for longer/higher fall factors, and they'll probably effectively reduce the fall length (as seen as force on the anchor) by 6'

Another thing worth pointing out is, assuming the rope/belay system acts the same with or without the screamer, the ~1' extension of the screamer, or ~2' in the case of he zipper, makes you stop your fall 2' and 4' closer to the ground, respectively.


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By Danger-Russ Gordon
From Tempe, AZ
Nov 21, 2012
Slope on a rope

Since we are on the hypothetical side of this debate in some respects, could you, hypothetically, connect several screamers, and if so would the advantages of force reduction be multiplied respectively to how many screamers you added? Just wondering if anyone has thoughts on that, I know its ridiculous.


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By Buff Johnson
Nov 21, 2012
smiley face

I typically use screamers so they let me know I'm climbing too slow, or for when we have no neighbors, possibly even a force mutliplier


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By rgold
From Poughkeepsie, NY
Nov 21, 2012
The traverse out to the Yellow Ridge on the Dogstick Ridge link-up.  Photo by Myriam Bouchard

Larry, you're a brave soul for actually trying to do a little physics on MP. I made a conscious decision not to do that, for fear of the opprobrium of the anti-sciency crowd, but we've seen how that worked out.

So here is a response. The 3-foot figure is mine, and it applies to the zipper screamer (2 foot extension) not the shorty. The glitch in your analysis is that you calculate the energy the screamer absorbs, but ignore the fact that, in extending, it adds to the fall distance and so also adds to the energy total that has to be absorbed by the system. I guesstimated the extension of a zipper screamer to be about 20 inches or 50 cm, since the loops on each end aren't part of the extension. So this gives a total energy-absorbing ability of (2447 N ) X (0.5 m) = 1224 J approximately.

But the screamer adds mgh=(80 kg)(9.8 m/sec^2)(0.5 m) or approximately 392 joules of potential energy to the fall total. That results in a net energy reduction due to the screamer of about 832 joules, corresponding to a fall of about 1 meter, which I called approximately 3 feet.

This analysis represents the best you could hope for from the longer screamer, not the shorter one. The CAI tests suggest you can't expect even that.

DRG, you could indeed link screamers for more energy absorbtion, the price being increased fall distance. The calculations above show that in order for the screamer to absorb all the fall energy, you need one screamer for every meter of fall, so a ten foot fall before screamer activation would need ten screamers, which would extend 200 inches or about 17 feet. However, this ignores the fact that the rope has to stretch until the tension in it exceeds 1.2 kN (or some smaller value if friction over the top biner is taken into account), the activation threshold of the screamer. That stretching will already have absorbed some fall energy, reducing the number of full-extension screamers needed.


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By Stich
From Colorado Springs, Colorado
Nov 21, 2012
Coffee after freezing our asses off near James Peak.

What is it that bothers some of you guys about what rgold is saying about screamers? Does it bother you that what he is saying contradicts what you believe? Does it shake your confidence in screamers just a bit? I really don't understand your reactions.

Thanks for outlining your thoughts so concisely, Richard. I read and enjoyed reading your above posts.


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By Stiles
From the Mountains
Nov 22, 2012
Rough

Who has got a piece of pro that was yanked with a screamer? Failure stories?

When contemplating real life Pain, l am always, always glad for every bit of advantage.


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By John Husky
Nov 22, 2012

Napkin physics is great in theory but in practice there are way too many variables in play to make perfect sense out of. The bottom line is that climbing gear has evolved to the point where it works, really well. So well that people are everywhere are able to half-ass it on crags the world over and still walk away.

To answer the OP, stick them on your first piece if you want, if you deck because of extension, the rope is going to be softening your landing to the point of no problem. Unless you have screwed the pooch, in which case your an idiot, or wicked rad.

I like to place them on fixed pins or other gear of unknown quality.

My partner used one on a spectacular ice fall of 20+ feet. He ended up standing on the snow slope at the bottom of the climb (single pitch). It was a nice soft catch, the screamer fully deployed, the screw was a good one. I clipped it on my way up while finishing the lead on pink point.

If you don't like them for reasons of your own, you should not use them.


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By John Husky
Nov 22, 2012

Hey, I didn't mean to imply that screamers work to reduce the forces in a fall by my anecdote. I do maintain that they work as draws.

You should clip one to your computer.


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By Stich
From Colorado Springs, Colorado
Nov 22, 2012
Coffee after freezing our asses off near James Peak.

I'm not so sure we can trust "sciencey" physics calculations "on a napkin."


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By patto
Nov 23, 2012

Stich wrote:
What is it that bothers some of you guys about what rgold is saying about screamers? Does it bother you that what he is saying contradicts what you believe?

Sadly that is the way that most people react to evidence and arguments that contradict their beliefs. Instead of considering the evidence and arguments and reassessing their beliefs they spend all their energy trying to contrive arguments and evidence to support they beliefs.** If they can't do they they simply try to discredit arguments that they don't want to believe.

A great example:

John Husky wrote:
Napkin physics is great in theory but in practice there are way too many variables in play to make perfect sense out of.

This 'napkin physics' is the same physics that got man to the moon.

Please elaborate on the other variables that are in play that would cause the screamer to absorb more energy? How would this lead to a lower peak force in the rope and thus on the gear?

There is a few other factors involved, you are right. And those factors act to make the screamer LESS effective than napkin physics suggests. The tests with a conventional belay (as opposed to a tied anchor) show that.


  • **Almost all of us have this INITIAL reaction to evidence that contradicts our beliefs. I can think of several examples where I have behaved this way. However the wise, will objectively reconsider and assess our beliefs continuously. There is no shame in admitting you are incorrect when you are incorrect. There is shame in not admitting it.


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By John Husky
Nov 23, 2012

Are you seriously not shitting me right now? The moon?

I guess I was thinking of rope drag at every possible point along the way, which is a lot of individual variables, and hard to quantify. But I am no NASA scientist, so I don't know much about load limiting doohickies. I do know they don't hurt, and I have some, so...


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By Reginald McChufferton
Nov 23, 2012

John Husky wrote:
Are you seriously not shitting me right now? The moon? I guess I was thinking of rope drag at every possible point along the way, which is a lot of individual variables, and hard to quantify. But I am no NASA scientist, so I don't know much about load limiting doohickies. I do know they don't hurt, and I have some, so...



You are right John. Screamers don't hurt. Just this afternoon I was fighting a 350 lb "woman" at Walmart over the last "Directors cut, platinum edition, Blueray, triple disc set of the Creature from the Black Lagoon"

I wipped out my screamer, that I recently clipped off to my key chain, cause ya know, it can't hurt, and started beating this fat bitch with it like I was trying to punish her for being born. Wouldn't ya know it. It didn't hurt her, even a little bit. Now, where the fuck am I gonna find that movie John?


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By rgold
From Poughkeepsie, NY
Nov 23, 2012
The traverse out to the Yellow Ridge on the Dogstick Ridge link-up.  Photo by Myriam Bouchard

I'm not so sure that screamers don't hurt. Here's what happened in the CAI tests I linked to above.

There was one test in which the drop weight was statically anchored and subjected to a 6m factor-1 fall. In this case, there was a 20% reduction in the load to the top piece when a screamer was used. So far, so good. The BD tests had a similar result too.

When a belayer was employed, the results are different. The tests employed both tube style belay devices and Munter hitches. There didn't seem to be any difference in terms of which method was used.

Five of the trials used a pair of half ropes both clipped to the anchor point---perhaps because it is common in Europe to clip both half ropes to the first piece. The fall factors involved were 0.5, 1, and 1.5, and the position of the belay was moved so that the fall itself was always 6 m. Four of the five trials saw small reductions in the load to the top anchor of 2%, 4%, 6%, and 8%, but in the fifth trial, (one of two 1.5 fall factor drops) the screamer added 9% to the anchor load.

There were two further trials, one with a single half rope clipped, as I think most US and British climbers would do, and one with a single full rope. Both of these trials had fall factors of 1.5 and used a munter hitch belay. The screamer added 11% to the single half rope anchor load and 18% to the single full rope anchor load.

The one place the screamer made a significant positive difference was in the totally static belay case. This suggests that climbers who are rope-soloing might profitably use a screamer on their anchor.

The screamer had a small effect with a two-half-rope system that is stiffer than a single strand of either a half rope or a full rope and is uncommonly used in the U.S.

When the fall was on either a single half or full rope, the screamer made things worse, with a single full rope, the preferred American system being the worse of those two cases.

In all cases, the screamer reduced the amount of rope that ran through the belay device on the way to stopping the fall. It appears from these tests that for bigger fall factors and the less stiff systems Americans use, this reduction in slippage actually produces higher anchor loads than would have been obtained without the screamer.

The unsurprising fact that screamers were more effective with either stiff or entirely static systems suggests, as I mentioned earlier, that they may be more useful when locking belay devices are employed, or when rope friction in the system makes the belay essentially static, an occurrence that is common for short falls that are not near the belayer. Ironically, this suggests the more likely place for screamer effect is on the high pieces, not the first few---the opposite of what conventional wisdom seems to dictate.

The article doesn't discuss or include information about how many drop events constituted each of these trials (I guess it could even have been one), and says nothing about the variation in performance of the belayers, if indeed there were multiple drops. Human belay performance is notoriously variable, and it is conceivable that these results reflect the range of human behaviors as much as screamer effect. Nonetheless, the tests certainly raise the possibility that, especially for severe falls close to the belay, screamers might be counterproductive.

I think it is worth noting that these results are now fourteen years old. The fact that information like this doesn't seem to make its way across the pond for most climbers is an indication of how backward we are in some ways. But it is also clear that the time is past due for an attempt to replicate the results. Today's ropes have lower impact forces, which would seem to put them in with the less stiff systems for which screamers were counterproductive. But today's belay devices have more friction and so stiffen up the systems, possibly making screamers more productive.

Even in the face of the uncertainties, I think one can make some rational decisions about if, when, and how to use screamers, with the understanding that new information could alter those choices. If I were to actually say what I would do with this information, I'd have to listen, for the umpteenth time, to the tiresome complaints about telling other climbers how to climb. So dear reader, if you've made it this far, I leave the conclusions to you, as it should be and always was.

Be careful out there my friends.


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By bearbreeder
Nov 24, 2012

perhaps someone can give me the odds of a screamer killing you ... vs. all the other way that do kill people in the accident reports ...

there is a huge disconnect between what people worry about on the intrawebs and what actually happens in real life ...

but then thats what makes MP so much fun for the umpteenth time ;)


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By Dana Bartlett
From CT
Nov 24, 2012

bearbreeder wrote:
perhaps someone can give me the odds of a screamer killing you ... vs. all the other way that do kill people in the accident reports ... there is a huge disconnect between what people worry about on the intrawebs and what actually happens in real life ... but then thats what makes MP so much fun for the umpteenth time ;)


I remember when the Nose was freed. This was touted as a groundbreaking event - more so after a few locals couldn't repeat it.


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By Mark Heyman
Nov 24, 2012

Thanks RG.

Darn. I was just starting to use screamers 14 yrs ago, not that my climbing strategy depended on them. The best time to process information and learn from it is not at the crag. You have me reconsidering.

Thanks this time as in so many past posts.


Mark


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By Buff Johnson
Nov 24, 2012
smiley face

It is counter intuitive they found added force being placed into a dynamic system.

Maybe a similar thought as by losing the first placement off the anchor making the rope in service less resilient. By the time you hit the anchor, possibly making peak force worse than if you had just forgone the placement and just went with a factor2, but had the rope with its full resilience.


I would offer that you might see a benefit if you deploy the screamer but not fully. Energy is being dissipated in some form here.


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By rgold
From Poughkeepsie, NY
Nov 24, 2012
The traverse out to the Yellow Ridge on the Dogstick Ridge link-up.  Photo by Myriam Bouchard

Buff, although it is convenient to speak of the results in terms of the screamer "adding" to the load, it certainly does sound counterintuitive that way. The fact is that you have two different dynamic systems and the end results of deploying them are different; neither one can be characterized in any physical sense as adding or subtracting to the results of the other.

I suspect that our intuitive feeling that the screamer is either going to help or at worst do nothing is based on an unacknowledged assumption that the belay is completely static, in which case there is some experimental confirmation for this idea. For severe falls with minimal friction in the system, i.e. on the first piece or two with the pieces in line with the belay, all experiments, including those with human belayers and fallers, confirm that rope will slip through the belay device, and the effects of this slippage are not part of our conventional thinking about load reduction.

What may be happening is that the initial small energy reduction produced by the screamer is enough to enable the belayer to hold on with less slippage, ultimately forcing the rope to stretch more and so develop higher anchor loads.

To understand how this countintuitive result could happen, consider the CAI test with the 6 m factor 1.5 fall on a single 10.5mm rope, the one with the worst outcome for the screamer. The belayer had about 5.5 feet of rope run through the device without the screamer and about two feet less rope with the screamer. In this case, the screamer shortened the amount of rope slipping through the device by approximately the same amount as the screamer extension. So if the resistance in the belay device/braking hand combination is higher than the screamer activation threshold, as it must be in order for the screamer to activate and fully deploy, then putting the screamer in the system dissipates less energy than the belay device/brake hand combination left alone, and so passes more energy to the rope to absorb, requiring more stretching and therefore higher tension and anchor loads.

So it isn't that the screamer didn't absorb fall energy, its just that slippage in the belay device would have absorbed more energy, and in that sense the screamer addition was counterproductive.

These observations are plausible but remain speculation. And as I mentioned earlier, it is not unreasonable to be concerned that the CAI data might be confounded by belayer performance variations. The situation does not lend itself to hard and fast pronouncements, although it does suggest some rational approaches to screamer use, at least unless or until better data are obtained.

You can, of course, take bearbreeder's approach that something else will get you anyway---except that if you actually believe that, you wouldn't be bothering with screamers in the first place.

I would also add that the thinking underlying the smart-alecky remark (if indeed there is any thinking) is flawed. There is no single thing in climbing that, by itself, has a high probability of killing you. But there are a host of low-probability events whose cumulative effect comprises the risk in climbing. The only possible approach to reducing risk is, in fact, to attend to a large number of low-probablity situations and try to make as many of them as possible a little less likely, in the hope that a collection of small reductions in many aspects will have a significant total effect. This makes it inevitable that we will end up conversing about things that, in isolation, can be said to be of little consequence.


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By brenta
From Boulder, CO
Nov 24, 2012
Cima Margherita and Cima Tosa in the Dolomiti di Brenta.  October 1977.

rgold wrote:
But the screamer adds mgh=(80 kg)(9.8 m/sec^2)(0.5 m) or approximately 392 joules of potential energy to the fall total.

Richard, a very small correction: if the screamer extends by d, the fall is lengthened by 2d.

To KC: since screamers absorb a bounded amount of energy, but they extend the fall by the same amount if they fully deploy, they reduce peak load less for bigger guys than for smaller ones. (Even to the point of increasing the peak load. No, life isn't fair.)

My additional 2c on the subject:

  • The "test data" on Yates's site look like no test data at all.

  • Since the effective spring "constant" of a rope is not constant at all, and, specifically, depends on the speed at which the rope is being stretched, the argument about the longer time the rope is given to stretch is not without merit.

  • In conclusion, for short falls by moderately heavy climbers without dynamic belay, there should be some advantage, as shown by the BD tests. For other situations, other factors may prevail, as shown by the CAI tests.


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By bearbreeder
Nov 24, 2012

well someone asked this earlier ... and ill repeat it ... how many people have screamers killed ...

now how many people have dropping belayers, rockfall, rap errors, etc ... killed

if you want to use a screamer intelligently ... go right ahead, if you dont ... well thats up to you as well ...

people go crazy over PASes, crossloaded belay biners, dyneema slings, etc ... when what they SHOULD be paying attention is the basic ...

i assume that everyone here wears a helmet all the time ... because that will save your life more than any screamer or lack thereoff ever will

id personally love to see people go up to each other at the crag and say "dude dont use a screamer, theyre uselss/deadly/etc ..." ... my first reponse would be "OK buddy, your lead on this climb, no screamers" ;)

i remember someone going off about how you must have lockers, purcells, and all the little things that didnt really matter ... what did he do? ... rap off the ends of his rope ...


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