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Yates Screamers, obsolete or niche?


Brian Izdepski · · Peshastin, WA · Joined Aug 2019 · Points: 0

In the same place it always is. So many variables in this sport, and not enough time or money for definitive research. Even if there was the perfect study, at most 60 percent of people would agree with it. I know that is not what a science or engineering person wants to hear. For me when there are so many variables involved, I like the idea of going with what makes sense, has been around for a while, and has had some really smart people paying for the technology. To each his own...

Jim Titt · · Germany · Joined Nov 2009 · Points: 490
Brian Izdepski wrote: In the same place it always is. So many variables in this sport, and not enough time or money for definitive research. Even if there was the perfect study, at most 60 percent of people would agree with it. I know that is not what a science or engineering person wants to hear. For me when there are so many variables involved, I like the idea of going with what makes sense, has been around for a while, and has had some really smart people paying for the technology. To each his own...

So it's acceptable to bring climbing equipment on the market without testing it's function and with no data to back up claims for the product? The screamer manufacturers have had several decades to do the testing and publish their results but they don't, why do you think this is?

Brian Izdepski · · Peshastin, WA · Joined Aug 2019 · Points: 0

I’ll let you know.

crewdog lm · · Nevada · Joined Dec 2010 · Points: 25
Jim Titt wrote:

So if there is factual evidence they work where is it?

I'm getting: there's no factual evidence that they DON'T work although, they may not work as well as we hoped. As I read this thread, there has indeed been testing  (by BD and by Yates) which substantiates the Screamer's ability to reduce impact force. The engineers who weighed in here suggested with compelling evidence, that the Screamer becomes less effective as the fall gets worse to the point that, a huge fall with a Screamer is just as bad as it would be without it. I agree with the last post: this has been a beneficial thread and suprisingly void of snarky a-hole comments (so far).

Roy Suggett · · Unknown Hometown · Joined Jul 2009 · Points: 8,119

crewdog, don,t you wish this civil thread could/would start a trend on MP.  Boy I do! 

climb 2 smile · · Draper, UT · Joined Apr 2015 · Points: 155

BD Test results

https://www.blackdiamondequipment.com/en_US/qc-lab-to-screamer-or-not-to-screamer.html

Jim Titt · · Germany · Joined Nov 2009 · Points: 490

Believe it or not a (working) link to that was posted as the fifth post on this thread

John Yates · · Unknown Hometown · Joined 14 days ago · Points: 0

I have enjoyed your posts on Screamers. I want to point out a few things though.. The BD testing only used standard screamers in their testing for fighter FF testing they should have used Zipper Screamers they activate also at 2 kN but elongate 22 inches a standard screamer is 11”. Thus absorbing twice as much potential energy. Thus the BD report that saw a 26% decrease in peak load would have shown at least 52% decrease. Also testing has shown that there is also a bonus in deceleration energy absorbed by your rope. By increasing the time of deceleration of the fall the rope is able to stretch and absorbe an additional amount of energy 10-20%. You can also increase the activation force from say 2kN to 4kN by hooking them side by side. So this may be advantagous on suspect bolts. So with two zippers used this way you could take a 12 kN event and reduce it to the activation force of 4kN. That is substantial. I have done countless other “StitchRippers” over the last 35 years for other deceleration testing for NASA, SpaceX, Boeing, US Military application. Screamers are really just one way bungee cords without the rebound.. we also use them in MT Rescue highline applications as basically field dynometers..

John Yates · · Unknown Hometown · Joined 14 days ago · Points: 0
Jim Titt wrote: The paper to read on why screamers have higher forces when the fall is larger is this;- https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwijz7Sdo5njAhXE16QKHRqZApgQFjAAegQIAhAC&url=http%3A%2F%2Fciteseerx.ist.psu.edu%2Fviewdoc%2Fdownload%3Fdoi%3D10.1.1.473.7055%26rep%3Drep1%26type%3Dpdf&usg=AOvVaw3eVQhFmoHtej6vPfKNHRb_

The time-prolonging efect is actually detrimental (we discussed this years ago, probably on RC.com). The peak force on the top piece is when the sum of the forces from the belayer AND the faller is greatest, due to hysterises through the system (primarily the rope) the two force curves are offset and delaying the peak force on the belayer actually increase the sum. The fall data I investigated the worst case was if the screamer added 0.3s if I remember rightly but it was a while ago I looked at this stuff.


rgold · · Poughkeepsie, NY · Joined Feb 2008 · Points: 526
John Yates wrote: I have enjoyed your posts on Screamers. I want to point out a few things though.. The BD testing only used standard screamers in their testing for fighter FF testing they should have used Zipper Screamers they activate also at 2 kN but elongate 22 inches a standard screamer is 11”. Thus absorbing twice as much potential energy. Thus the BD report that saw a 26% decrease in peak load would have shown at least 52% decrease. Also testing has shown that there is also a bonus in deceleration energy absorbed by your rope. By increasing the time of deceleration of the fall the rope is able to stretch and absorbe an additional amount of energy 10-20%. You can also increase the activation force from say 2kN to 4kN by hooking them side by side. So this may be advantagous on suspect bolts. So with two zippers used this way you could take a 12 kN event and reduce it to the activation force of 4kN. That is substantial. I have done countless other “StitchRippers” over the last 35 years for other deceleration testing for NASA, SpaceX, Boeing, US Military application. Screamers are really just one way bungee cords without the rebound.. we also use them in MT Rescue highline applications as basically field dynometers..

Links to where these various test results are published would be helpful.

Brian Izdepski · · Peshastin, WA · Joined Aug 2019 · Points: 0

John has plenty of tests and reply’s and will be replying soon. For some reason, he wasn’t allowed to repost quickly? He’s completely certain of the benefits of correctly using his load limiters, and is interested in doing more testing. Using the correct product for the situation is critical. Personally, I’m interested in testing to failure on some suspect rock, and then seeing about replicating with load limiters involved. Stay tuned.

Ryan O · · Portland, OR · Joined Nov 2007 · Points: 51
John Yates wrote: I have enjoyed your posts on Screamers. I want to point out a few things though.. The BD testing only used standard screamers in their testing for fighter FF testing they should have used Zipper Screamers they activate also at 2 kN but elongate 22 inches a standard screamer is 11”. Thus absorbing twice as much potential energy. Thus the BD report that saw a 26% decrease in peak load would have shown at least 52% decrease. Also testing has shown that there is also a bonus in deceleration energy absorbed by your rope. By increasing the time of deceleration of the fall the rope is able to stretch and absorbe an additional amount of energy 10-20%. You can also increase the activation force from say 2kN to 4kN by hooking them side by side. So this may be advantagous on suspect bolts. So with two zippers used this way you could take a 12 kN event and reduce it to the activation force of 4kN. That is substantial. I have done countless other “StitchRippers” over the last 35 years for other deceleration testing for NASA, SpaceX, Boeing, US Military application. Screamers are really just one way bungee cords without the rebound.. we also use them in MT Rescue highline applications as basically field dynometers..

I enjoyed reading your post and found it helpful. For the sake on the 130 something reply argument, I think you could provide a further service by producing a, “TL/DR” version of your original post though. 

Jim Titt · · Germany · Joined Nov 2009 · Points: 490
Brian Izdepski wrote: John has plenty of tests and reply’s and will be replying soon. For some reason, he wasn’t allowed to repost quickly? He’s completely certain of the benefits of correctly using his load limiters, and is interested in doing more testing. Using the correct product for the situation is critical. Personally, I’m interested in testing to failure on some suspect rock, and then seeing about replicating with load limiters involved. Stay tuned.

Well the discussion has been going on for the past 15 years or so, no rush for some real data.

The only testing in a scenario where the rope is belayed as normal AND with varying falls is from the CAI and their conclusions were:-
"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)."
rgold · · Poughkeepsie, NY · Joined Feb 2008 · Points: 526

In addition to links to published research documenting claims, I'd be interested in a clear explanation of how "increasing the time of deceleration of the fall the rope is able to stretch and absorb an additional amount of energy..." As far as I know, energy absorbed is proportional to the square of  the amount of relative stretch, so it would help to hear how the amount of time it takes to achieve that stretch changes the energy absorbtion.  Moreover, since the screamer is a load limiter (at least on average), the constant load during screamer activation means the rope isn't stretching at all, and that rope stretch only occurs leading up to screamer activation and following full deployment.  This would mean there would be no rope activity during screamer deployment, so where is the extra energy absorbtion coming from?  (There is, by the way, a possible explanation of rope energy absorbtion based on the fact that the screamer causes not a constant load but an oscillating one, but no one has said anything about that and it would require an extremely rapid recovery by the rope in order to work.)

The quote seems to suggest that the rope stretches more than it would without the screamer, which of course would result in higher loads, not lower ones.

Correct me if I'm wrong, but in the military and industrial applications of screamer-like technology, the load limiters are the only energy-absorbing devices, and calculations made ahead of time dictate the appropriate screamer properties and the number of screamers required for the application.  Is there any military/industrial application in which the primary task of energy absorbtion is something else (in the case of climbing, the rope) and the load limiter is present as some sort of supplement or enhancer of that primary mode?  Because that's the climbing situation, and it isn't clear that the military and industrial uses are relevant.

rocknice2 · · Montreal, QC · Joined Nov 2006 · Points: 3,184

It seems to me that the screamer has a maximum amount of energy that it can absorb. Even this may be different considering how its deployed [high speed vs low speed].
If I take Jim's data of 1.2kJ  as the total energy the screamer can absorb, until fully deployed.
This leaves me with some simple calculations.
J=1/2*M*V^2,  1200=.5*80*V^2 ... so V=5.5m/s
If I plug the velocity into a free fall calculator I get a distance of 1.54 meters. This is just the screamer.
The rope can absorb as well, so lets double it. 3 meters ?? I'm not taking into account that the screamer adds to the fall distance.

So a climber can climb up 1.5m above their last pro before it fully deploys. That's basically at your feet.

This is just a back-of-the-sleeve calculation and it's definitely more complicated than this.
I doubt the final results are going to be vastly different. Definitely not going to triple the distances to 4.5 meters.

Jim Titt · · Germany · Joined Nov 2009 · Points: 490

Nice edit! I too have been pondering on this during the day as we once tried to research varying the impact speed (time) while keeping the force the the same. There is hysterises in the rope stretch but what the relationship between rate of strain is proved impossible to measure, either our measuring equipment wasn't good enough or the effect is so minimal as to be undetectable. (It's one of those tests that costs a fortune, probably $5000 in the end). Personally I'm thinking it's just a theory with nothing to back it up.

George Bracksieck · · Unknown Hometown · Joined Oct 2008 · Points: 1,503
rgold wrote: In addition to links to published research documenting claims, I'd be interested in a clear explanation of how "increasing the time of deceleration of the fall the rope is able to stretch and absorb an additional amount of energy..." As far as I know, energy absorbed is proportional to the square of  the amount of relative stretch, so it would help to hear how the amount of time it takes to achieve that stretch changes the energy absorbtion.  Moreover, since the screamer is a load limiter (at least on average), the constant load during screamer activation means the rope isn't stretching at all, and that rope stretch only occurs leading up to screamer activation and following full deployment.  This would mean there would be no rope activity during screamer deployment, so where is the extra energy absorbtion coming from?  (There is, by the way, a possible explanation of rope energy absorbtion based on the fact that the screamer causes not a constant load but an oscillating one, but no one has said anything about that and it would require an extremely rapid recovery by the rope in order to work.)

The quote seems to suggest that the rope stretches more than it would without the screamer, which of course would result in higher loads, not lower ones.

Correct me if I'm wrong, but in the military and industrial applications of screamer-like technology, the load limiters are the only energy-absorbing devices, and calculations made ahead of time dictate the appropriate screamer properties and the number of screamers required for the application.  Is there any military/industrial application in which the primary task of energy absorbtion is something else (in the case of climbing, the rope) and the load limiter is present as some sort of supplement or enhancer of that primary mode?  Because that's the climbing situation, and it isn't clear that the military and industrial uses are relevant.

Force equals mass times acceleration. Deceleration is negative acceleration. When a fall is arrested over a greater amount of time, the impact force is reduced. Energy absorbed is the force absorbed over a distance. 

The biggest Screamer can absorb more energy. Screamers attached IN SERIES can absorb yet more energy and would help to prevent exhaustion of the load-limiting benefit. A big fall, however, would instantly exhaust the Screamer(s), which, because fully deployed, adds to the distance of the fall without substantially increasing the time during the fall is arrested. The rope only begins to absorb energy after this increase in the fall distance, thereby increasing the impact. 

If you fall from a meter or so above a marginal piece of pro, a big Screamer may help it catch your fall and prevent a longer fall. 
Jim Titt · · Germany · Joined Nov 2009 · Points: 490
rocknice2 wrote: It seems to me that the screamer has a maximum amount of energy that it can absorb. Even this may be different considering how its deployed [high speed vs low speed].
If I take Jim's data of 1.2kJ  as the total energy the screamer can absorb, until fully deployed.
This leaves me with some simple calculations.
J=1/2*M*V^2,  1200=.5*80*V^2 ... so V=5.5m/s
If I plug the velocity into a free fall calculator I get a distance of 1.54 meters. This is just the screamer.
The rope can absorb as well, so lets double it. 3 meters ?? I'm not taking into account that the screamer adds to the fall distance.

So a climber can climb up 1.5m above their last pro before it fully deploys. That's basically at your feet.

This is just a back-of-the-sleeve calculation and it's definitely more complicated than this.
I doubt the final results are going to be vastly different. Definitely not going to triple the distances to 4.5 meters.

Conservation of energy is a blunt tool when it comes to forces, when it comes to considering a completeystem (faller, top piece and belayer) things are more difficult which is why drop tests with a fixed point are worthless. We know experimentally that the peak force on the top piece is made up when the sum of the force on the faller and the belayer is greatest. Not the sum of the two peak forces as they occur at different times . The peak on the belayer occurs earlier than that of the faller so delaying the effect on the belayer makes the total force higher. If you can delay it enough then one is back in the plus side but a screamer is unlikely to take long enough (you can read that as it won't happen).

rgold · · Poughkeepsie, NY · Joined Feb 2008 · Points: 526
George Bracksieck wrote:

Force equals mass times acceleration. Deceleration is negative acceleration. When a fall is arrested over a greater amount of time, the impact force is reduced. Energy absorbed is the force absorbed over a distance. 

None of this addresses anything I asked.  You say "When a fall is arrested over a greater amount of time, the impact force is reduced."  But the "impact force" is a peak load and nothing you've said (including F=ma, which is for constant acceleration), explains how the lengh of time to arrest affects the peak load.   If longer time somehow automatically equated to lower peak load, then a long factor k fall would have a lower peak load than a short factor k fall, because the arresting time is longer.  

Jim Titt · · Germany · Joined Nov 2009 · Points: 490
George Bracksieck wrote:

Force equals mass times acceleration. Deceleration is negative acceleration. When a fall is arrested over a greater amount of time, the impact force is reduced. Energy absorbed is the force absorbed over a distance. 

The biggest Screamer can absorb more energy. Screamers attached IN SERIES can absorb yet more energy and would help to prevent exhaustion of the load-limiting benefit. A big fall, however, would instantly exhaust the Screamer(s), which, because fully deployed, adds to the distance of the fall without substantially increasing the time during the fall is arrested. The rope only begins to absorb energy after this increase in the fall distance, thereby increasing the impact. 

If you fall from a meter or so above a marginal piece of pro, a big Screamer may help it catch your fall and prevent a longer fall. 

You are replying to professor of mathematics. That screamers may be of benefit in short falls is not the discussion, that you can extrapolate this to larger falls is.

Guideline #1: Don't be a jerk.

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