|
brunoschull
Oct 7, 2013, 4:02 AM
Post #1 of 20
(31406 views)
Shortcut
Registered: Nov 10, 2004
Posts: 47
|
A while back, I read an interesting interview with Kitty Calhoun, Bill Belcourt, Michael Kennedy, Jack Tackle, and Jay Smith. Among other things (leashes, tethers) they discuss screamers. Bill's position seems to be that screamers don't really do much, if anything. A screamer absorbs some energy in a fall, but it also extends the distance of a fall, so you don't gain much. A zero sum game. Thoughts? Do screamers add any real practical safety?
Link to interview below:
http://www.chickswithpicks.net/gear-2/kitty-calhoun-interview-with-bill-belcourt-of-black-diamond-with-michael-kennedy-jack-tackle-and-jay-smith/
|
|
|
|
|
USnavy
Oct 7, 2013, 4:10 AM
Post #2 of 20
(31403 views)
Shortcut
Registered: Nov 6, 2007
Posts: 2667
|
brunoschull wrote: A while back, I read an interesting interview with Kitty Calhoun, Bill Belcourt, Michael Kennedy, Jack Tackle, and Jay Smith. Among other things (leashes, tethers) they discuss screamers. Bill's position seems so be that screamers don't really do much, if anything. A screamer absorbs some energy in a fall, but it also extends the distance of a fall, so you don't gain much. A zero sum game. Thoughts? Do screamers add any real practical safety? Link to interview below: http://www.chickswithpicks.net/gear-2/kitty-calhoun-interview-with-bill-belcourt-of-black-diamond-with-michael-kennedy-jack-tackle-and-jay-smith/
The same thing that can be applied to screamers can be applied to high-elongation ropes. They increase the chance of the piece holding but also increase your fall distance. You have to decide for yourself if it is worth it or not.
As far as a screamer's effectiveness goes, it depends a lot on how much energy the screamer can absorb relative to the fall distance. If you are taking a 100 footer on a piece, a screamer wont do much because there is already so much energy involved in the fall. But if you fall on the piece with it at your foot, the screamer will make a difference. Yates has some graphs showing how much of a different they make. Screamers are most effective at absorbing energy in a high-impact, low-distance fall. The best example would be using a screamer to clip the first piece out of the belay where the fall factor is over one and the fall distance is short.
(This post was edited by USnavy on Oct 7, 2013, 4:14 AM)
|
|
|
|
|
granite_grrl
Oct 7, 2013, 2:48 PM
Post #3 of 20
(31318 views)
Shortcut
Registered: Oct 25, 2002
Posts: 15084
|
brunoschull wrote: A while back, I read an interesting interview with Kitty Calhoun, Bill Belcourt, Michael Kennedy, Jack Tackle, and Jay Smith. Among other things (leashes, tethers) they discuss screamers. Bill's position seems to be that screamers don't really do much, if anything. A screamer absorbs some energy in a fall, but it also extends the distance of a fall, so you don't gain much. A zero sum game. Thoughts? Do screamers add any real practical safety? Link to interview below: http://www.chickswithpicks.net/...ackle-and-jay-smith/
It depends. I use screamers when ice climbing. I'd rather take a 20ft fall bouncing down the ice than a 40ft fall bouncing down the ice after a screw rips.
There was talk that they don't work. Not working means that they don't deploy, if they do deploy to lengthen a fall they have worked (ie - they used energry to deploy). It's trade offs, which Bill doesn't seem to address and nobody in the interview questions him on?
Obviously you have to be aware of their limitations and use them accordingly.
|
|
|
|
|
brunoschull
Oct 7, 2013, 3:44 PM
Post #4 of 20
(31302 views)
Shortcut
Registered: Nov 10, 2004
Posts: 47
|
Thanks for the replies so far. I have always used screamers as suggested; for first placements off belays, and for marginal placements, mostly when ice climbing. But I do not want to dismiss Bill's statements in the interview so quickly; do most climbers think that screamers can do more than actually possible?
If I understand correctly, when a screamer deploys, it absorbs energy by the stitching ripping, and by allowing more time/rope elongation. At the same time, when a screamer deploys, a climber will fall a greater distance, and presumably accelerate, adding more energy to the fall. How do these two things balance? I would love to see some numbers for this. Anybody want to generate some hypothetical numbers for two scenarios at the extremes, for example, short factor two fall, and a long fall with a lower fall factor? If I had the knowledge and math skills, I would do it myself :)
All the best, and thanks again.
Bruno
|
|
|
|
|
patto
Oct 7, 2013, 4:44 PM
Post #5 of 20
(31276 views)
Shortcut
Registered: Nov 15, 2005
Posts: 1453
|
There is very little evidence to suggest that screamer have much more than negligible effect to peak loads. A climbing rope is far better and more important. If you want to reduce peak loads then use half ropes or a single rope that is more stretch than most (Beal ropes). This will make far bigger difference.
Without getting too in depth a screamer will absorb energy at a rate of 3G. Meanwhile you are being accelerated at 1G.
|
|
|
|
|
JimTitt
Oct 7, 2013, 6:33 PM
Post #6 of 20
(31246 views)
Shortcut
Registered: Aug 7, 2008
Posts: 1002
|
From the technical commitee of the Italian alpine Club wh did extensive drop tests on screamers using various belay devices. My translation.
"It was confirmed that the examined device has an ability to absorb potential energy, that is 120-130kgm (1.18-1.23kJ), as was seen from of the data of the drop tests executed on the drop tower with a fixed rope and from the dynamometer tests carried out in the laboratory. It was also confirmed that actuation (that is the rupture of seams) occured consistently for all the dozen of tests carried out at a load of ca.2.2kN. But, of more interest to the climber, it was also confirmed that it was insufficiently useful in the aim of reducing the load on the last runner, as is seen clearly from the results of the dynamic tests. In all the testing conditions in fact, the presence of the shock-absorber has turned out practically negligeable in the sense that the reduction of the load on the runner was nearly always insignificant, and additionally, in high force situations (ca. 8kN) and with
moderate braking force from the belayer the loads on the top runner were increased.
In light of its insufficient ability to absorb energy one thinks therefore that such device can be of guaranteed usefullness only when the total energy in the system is relatively low, that is in the event of heights of fall of few meters (e.g. a fall from ca. 1m above the runner)."
For aid climbing there could be a rationale, for the rest the belayer does the job.
|
|
|
|
|
brunoschull
Oct 7, 2013, 7:09 PM
Post #7 of 20
(31232 views)
Shortcut
Registered: Nov 10, 2004
Posts: 47
|
Thanks JT. That just about sums up my suspicion. Not sure I'll carry these on my ice climbing rack anymore. All the best, B.
|
|
|
|
|
sittingduck
Oct 7, 2013, 7:56 PM
Post #8 of 20
(31214 views)
Shortcut
Registered: Aug 19, 2003
Posts: 338
|
Who would have thought - screamers are over rated.
I've also carried at least one of them while ice climbing - until now ...
Thanks for the info :)
|
|
|
|
|
brunoschull
Oct 8, 2013, 6:11 AM
Post #9 of 20
(31165 views)
Shortcut
Registered: Nov 10, 2004
Posts: 47
|
Thanks again for the replies. Just to summarize, it seems that screamers may work best for short falls, for example, about a meter above the first piece off an anchor, or aid climbing, while screamers probably don't do anything at all, and may even increase the forces on the top piece, for longer distance falls.
For me, this is too limited an application to carry screamers ice climbing. Think of the things that would have to come together to make a screamer worthwhile; a marginal placement and/or difficult moves right off a belay, no ledge to hit on the way down with the added fall distance, and do on. As I said, too limited a situation.
In fact, for ice climbing, I would say that it might be safer not to carry screamers. The way that I have always used screamers, and, from what I have seen, the way that most people use screamers, is to add some safety (or the feeling of safety) to marginal placements. If we have screamers on our rack, we will probably place a marginal piece, clip a screamer, and keep going, hoping that it will hold. Better to not have the screamer, and force ourselves to look for better placements, and think clearly about the consequences of continuing higher.
I don't do any aid climbing (except the odd bit of pulling on gear now and again) so I can't really speak to that application, but it seems like screamers might have their place on big walls.
OK, thanks again, Bruno
|
|
|
|
|
USnavy
Oct 8, 2013, 8:40 AM
Post #10 of 20
(31154 views)
Shortcut
Registered: Nov 6, 2007
Posts: 2667
|
JimTitt wrote: From the technical commitee of the Italian alpine Club wh did extensive drop tests on screamers using various belay devices. My translation. "It was confirmed that the examined device has an ability to absorb potential energy, that is 120-130kgm (1.18-1.23kJ), as was seen from of the data of the drop tests executed on the drop tower with a fixed rope and from the dynamometer tests carried out in the laboratory. It was also confirmed that actuation (that is the rupture of seams) occured consistently for all the dozen of tests carried out at a load of ca.2.2kN. But, of more interest to the climber, it was also confirmed that it was insufficiently useful in the aim of reducing the load on the last runner, as is seen clearly from the results of the dynamic tests. In all the testing conditions in fact, the presence of the shock-absorber has turned out practically negligeable in the sense that the reduction of the load on the runner was nearly always insignificant, and additionally, in high force situations (ca. 8kN) and with moderate braking force from the belayer the loads on the top runner were increased. In light of its insufficient ability to absorb energy one thinks therefore that such device can be of guaranteed usefullness only when the total energy in the system is relatively low, that is in the event of heights of fall of few meters (e.g. a fall from ca. 1m above the runner)." For aid climbing there could be a rationale, for the rest the belayer does the job.
Do you have the original study? I would like to see it.
On a side note, Yates claims that screamers have a very profound effect on limiting the impact force of the top piece.
http://www.yatesgear.com/climbing/screamer/use.htm
Also, Black Diamond found that screamers are effective in its testing.
http://blackdiamondequipment.com/en/qc-lab-to-screamer-or-not-to-screamer.htmlhttp://blackdiamondequipment.com/en/qc-lab-to-screamer-or-not-to-screamer.html
It is interesting that this subject came up because screamer testing is on my list of topics to explore, among other things.
One thing for sure, energy-absorbing slings like screamers absolutely limit the impact force when used in situations where no other dynamic elements are present. For example, large "screamers" are extremely common in via ferrata lanyards and commercial rigging equipment, such as the lanyard that is designed to be connected to the Petzl ASAP. In those applications, falling without a specialized energy absorber could prove potentially lethal, or at the minimal, quite damaging, even if the user substituted the lanyard for dynamic rope.
However, via ferrata "screamers" seem to have a much higher initial trigger impact force requirement and far greater energy absorption capability than traditional screamers. I have fallen on a via ferrata lanyard and it was quite rough--very far from a soft catch for sure.
Last, some more info: http://www.mountainproject.com/v/do-screamers-work/105947850
(This post was edited by USnavy on Oct 8, 2013, 8:59 AM)
|
|
|
|
|
patto
Oct 8, 2013, 9:00 AM
Post #11 of 20
(31142 views)
Shortcut
Registered: Nov 15, 2005
Posts: 1453
|
USnavy wrote: Do you have the original study? Yates claims that screamers have a very profound effect on limiting the impact force of the top piece.
USnavy wrote: Also, Black Diamond found that screamers are effective in its testing. http://blackdiamondequipment.com/en/qc-lab-to-screamer-or-not-to-screamer.html
USnavy wrote: One thing for sure, energy-absorbing slings like screamers absolutely limit the impact force when used in situations where no other dynamic elements are present.
|
|
|
|
|
JimTitt
Oct 8, 2013, 11:42 AM
Post #12 of 20
(31124 views)
Shortcut
Registered: Aug 7, 2008
Posts: 1002
|
USnavy wrote: JimTitt wrote: From the technical commitee of the Italian alpine Club wh did extensive drop tests on screamers using various belay devices. My translation. "It was confirmed that the examined device has an ability to absorb potential energy, that is 120-130kgm (1.18-1.23kJ), as was seen from of the data of the drop tests executed on the drop tower with a fixed rope and from the dynamometer tests carried out in the laboratory. It was also confirmed that actuation (that is the rupture of seams) occured consistently for all the dozen of tests carried out at a load of ca.2.2kN. But, of more interest to the climber, it was also confirmed that it was insufficiently useful in the aim of reducing the load on the last runner, as is seen clearly from the results of the dynamic tests. In all the testing conditions in fact, the presence of the shock-absorber has turned out practically negligeable in the sense that the reduction of the load on the runner was nearly always insignificant, and additionally, in high force situations (ca. 8kN) and with moderate braking force from the belayer the loads on the top runner were increased. In light of its insufficient ability to absorb energy one thinks therefore that such device can be of guaranteed usefullness only when the total energy in the system is relatively low, that is in the event of heights of fall of few meters (e.g. a fall from ca. 1m above the runner)." For aid climbing there could be a rationale, for the rest the belayer does the job. Do you have the original study? I would like to see it. On a side note, Yates claims that screamers have a very profound effect on limiting the impact force of the top piece. http://www.yatesgear.com/climbing/screamer/use.htm Also, Black Diamond found that screamers are effective in its testing. http://blackdiamondequipment.com/en/qc-lab-to-screamer-or-not-to-screamer.htmlhttp://blackdiamondequipment.com/en/qc-lab-to-screamer-or-not-to-screamer.html It is interesting that this subject came up because screamer testing is on my list of topics to explore, among other things. One thing for sure, energy-absorbing slings like screamers absolutely limit the impact force when used in situations where no other dynamic elements are present. For example, large "screamers" are extremely common in via ferrata lanyards and commercial rigging equipment, such as the lanyard that is designed to be connected to the Petzl ASAP. In those applications, falling without a specialized energy absorber could prove potentially lethal, or at the minimal, quite damaging, even if the user substituted the lanyard for dynamic rope. However, via ferrata "screamers" seem to have a much higher initial trigger impact force requirement and far greater energy absorption capability than traditional screamers. I have fallen on a via ferrata lanyard and it was quite rough--very far from a soft catch for sure. Last, some more info: http://www.mountainproject.com/v/do-screamers-work/105947850
http://www.caimateriali.org/index.php?id=27
Clearly in the abscence of some other dynamic element screamers have some effect but that isnŽt how they are used in normal climbing, the relationship between the screamer activating, rope stretch and slip in the belay device is the critical issue and the results are then different.
The difficulty (or failing) for screamers is that for a given activation force the energy absorbed is too low (work of failure in engineering terms) whereas the frictional types can be arranged to give a low activation force and a high energy absorption.
The relationship between the braking force, faller force and top piece force is extremely complicated particularly related to the time scale and there is no model available for this so simple predictions are out. Best of luck with testing!
|
|
|
|
|
majid_sabet
Oct 18, 2013, 5:49 PM
Post #13 of 20
(30747 views)
Shortcut
Registered: Dec 13, 2002
Posts: 8390
|
screamers probably works best in rope access and industrial climbing and rigging applications where everything is static and falls are short but in climbing, the dynamic rope is the best option to reduce shock loads.
Long ago ,I only saw one screamer deployed on El Cap when leader took a 100 footer and belayer ended up with brunet hand and I don't know if screamer made much of difference .
IMO, if screamer pops,something bad is headed your way
worth to mentions that I climbed with Jack Tackel in Teton once and he is a very nice man with a world full of experience .
|
|
|
|
|
rgold
Oct 20, 2013, 3:53 PM
Post #14 of 20
(30622 views)
Shortcut
Registered: Dec 3, 2002
Posts: 1804
|
Here are some simplistic back-of-the-envelope calculations to think about. A Screamer elongates two feet, and has an activation level of about 550 lbf. If it totally deploys, it can absorb 2 X 550=1100 ft-lbs of energy. However, the two foot elongation causes the climber to fall an additional four feet. For a 180 lb climber, this adds 4 X 180 = 720 ft-lbs to the total energy that has to be absorbed. Consequently, a Screamer that fully deploys would remove a net 1100-720=380 ft-lbs of energy from the total to be absorbed for a 180 lb climber. I think the way to think about this is that the load to the top pro is about what you'd expect from a fall that was two feet shorter. In other words, it would be as if the leader fell a foot closer to the top piece.
That's what you can expect to get from a Screamer, a one-foot reduction in your fall position.
The fact that the reduction is absolute means that the Screamer effect becomes negligible as the length of the fall increases. I think one can see a hint of this absolute nature in the BD tests, in which the Screamer lowers the load to the top piece by about the same amount for the two different fall heights tested.
Of course, this doesn't work when the climber is one foot above the pro, the reason being that I assumed that the Screamer would completely deploy. So it would be better to say that the Screamer limits the load to the top piece to 550 lbf until it completely deploys, and thereafter reduces the load to the top piece to an amount associated with a two-foot shorter fall.
To get complete deployment, your 180 pound leader would have to fall about 1100/180 = 6 feet or so, i.e. be about 3 feet above the top piece. So if you are 3 feet above the top piece and fall with a Screamer, you get a load you'd expect from being two feet above the top piece instead.
None of this takes into account the complicated dynamics involved in the interactions from deformable belayer and climber and the effects of any slippage through the belay device. It seems likely to me that the variations that come from these effects might overwhelm the small Screamer contribution, so that in more realistic tests it would become difficult to notice any consistent Screamer effect. This seems to be what happened in the CAI tests referenced by Jim, where in some cases the Screamer-mediated belay actually does worse. (I should add that there is also a hypothetical explanation for why a Screamer might actually raise the load to the top piece by reducing the amount of slippage through the belay device that would otherwise have occurred.)
The numbers on the Yates site seem to me to be out of whack with any theoretical possibility, and as far as I know have never been even remotely confirmed by testing by anyone else. Yates actually admits the fact that the numbers don't seem to be realistic, and proposes a mechanism in which the Screamer causes the fall to be arrested over a longer period of time. Since the energy absorbed is the same regardless of how long it takes to absorb it, this does not make it clear why the peak force should be reduced. (It could account for how rapidly the peak force builds up, however, and that might have an effect on the extraction or breaking of gear, but that isn't the conclusion proposed.)
One way extra time might actually work has to do with the fact that the rope acts like a damped harmonic oscillator, and the damping force depends in some way on velocity. Since the Screamer lowers the velocity of the falling climber as seen by the rope, it would also lower the contribution to the total tension in the rope provided by the damping mechanism, and in that way might contribute to lowering the total load to the top piece. This could explain some of the Screamer effect, but there don't seem to be any tests that indicate that effect is anywhere near the Yates site claims.
|
|
|
|
|
JimTitt
Oct 20, 2013, 5:21 PM
Post #15 of 20
(30608 views)
Shortcut
Registered: Aug 7, 2008
Posts: 1002
|
Hi Richard
Well, one area to look at is the velocity, obviously a longer fall rips the screamer faster since the climber is falling faster.
The actual ripping of a screamer is somewhat complicated as the threads slide under tension until they break and if you test at different speeds you get different peak loads for an identical item:-
Semi-static pull test
Screamer 3m/s
Screamer 6m/s
So screamer theory is going to be a bit more complex than one might have hoped.
In fact vastly more complex;- if we are going to look at claims that time is of the essence as well then we need to look at the consequences of adding a delay in the rope tensions on top point.
For a pretty typical belay plate like an ATC XP the forces look like the left diagram where the maximum force on the top point (red line) is more or less where the sum of the tensions on the faller side (red line) and the belayer side (blue line) is highest. Delay the force on the faller side (which a screamer will do) and one may well end up in the situation shown on the right hand diagram where unfortunately the two peaks coincide.
Looks like someone is going to have to do a lot of very expensive and laborious testing to get a theory why they probably donŽt work!
|
|
Attachments:
|
Screamersemistatic.png
(46.8 KB)
|
|
|
Screamer3ms.png
(50.6 KB)
|
|
|
Screamer6ms.png
(52.0 KB)
|
|
|
Screamerbelayforce.jpg
(35.1 KB)
|
|
|
|
|
rgold
Oct 20, 2013, 5:33 PM
Post #16 of 20
(30603 views)
Shortcut
Registered: Dec 3, 2002
Posts: 1804
|
Very interesting Jim! It is such a pleasure to see some results from someone who actually has some insight into what is going on.
The one thing I'd add is that everything you've mentioned seems to point to less Screamer effect than I mentioned with my extremely simplistic arguments, or at least to more variation in the Screamer contributions, making it even less likely that a clear case for a positive effect can be consistently observed.
|
|
|
|
|
brunoschull
Oct 20, 2013, 6:38 PM
Post #17 of 20
(30590 views)
Shortcut
Registered: Nov 10, 2004
Posts: 47
|
Thanks again everybody. There is some great knowledge in this site. I really appreciate the contribution. All the best.
|
|
|
|
|
JimTitt
Oct 20, 2013, 9:05 PM
Post #18 of 20
(30573 views)
Shortcut
Registered: Aug 7, 2008
Posts: 1002
|
"making it even less likely that a clear case for a positive effect can be consistently observed"
Nice, did you borrow that from a politician? IŽll remember that as a more elegant version of my normal "and pigs might fly"!
|
|
|
|
|
rgold
Oct 21, 2013, 2:20 AM
Post #19 of 20
(30542 views)
Shortcut
Registered: Dec 3, 2002
Posts: 1804
|
Although pig aerodynamics are less than ideal, an appropriate although probably rare combination of circumstances might, in some cases, lead to airborne incidents that some might view as examples, however brief, of flight.
(This post was edited by rgold on Oct 21, 2013, 2:23 AM)
|
|
|
|
|
curt
Oct 21, 2013, 7:01 PM
Post #20 of 20
(30455 views)
Shortcut
Registered: Aug 27, 2002
Posts: 18275
|
Curt
|
|
|
|
|
|
