Soft catch vs. hard catch

Patrik wrote:

Hmmm... any chance you could help me read the graphs in this publication:
http://mra.org/wp-content/uploads/2016/05/Beverly_Sequential_Falls2.pdf

The way I read for example fig 6 through fig 10 is that peak force on the top piece of gear always aligns with maximum elongation of the rope (which in my mind would be when the falling climber "bottoms out"). What am I misreading here?

I think we can just ignore the theoretical discussion in the paper; it appears that the graphs are from real world testing which would include nonlinearities, frictional forces, etc.

Just to clarify: When I say "bottom out" of the falling climber, I mean at the time when the rope is stretched the most. After this, there is usually a bit of bounce back before the "system" settles down and is in "rest" (stationary). 

The problem is there is no belayer/belay device slip in those tests, if you test with a conventional device like an ATC you see the three force curves are offset in time and the top piece force curve is at any one time is the sum of the other two at the same time. I´ve some graphs somewhere but it´s midnight here!

RG as usual says it best. Sentiments that I have been thinking for years. In large part the soft catch is mostly annother excuse to shift blame on to the belayer and away from the person who actually screwed up and fell.  

Jim Titt wrote:

The problem is there is no belayer/belay device slip in those tests, if you test with a conventional device like an ATC you see the three force curves are offset in time and the top piece force curve is at any one time is the sum of the other two at the same time. I´ve some graphs somewhere but it´s midnight here!

Aha, this is very true. The publication with measured tests that I mentioned basically nails a grigri to a log. 

Yes, I tried to start my description with a "hard catch" (As I wrote: So for a hard catch, the force on the top piece of gear (and climber) is increasing from 0 to its maximum value when the climber "bottoms out") and then explain in a non-engineering fashion what would be needed to do to achieve a dynamic belay. Basically, when Alexz is belaying Old Lady H pulling a gnarly overhang. 

Trying to explain there are two different peak forces that are shifting in time and the sum is generating .... is probably going to lose most non-engineers around here. 

I still stick to my main point: A true dynamic belay attempting to significantly reduce the peak force on the top piece is considerably harder to do than the "soft catch" that sport climbers are asking for to keep them away from slamming into a wall. These are two very different tasks. Even if someone brags about being successful in the latter, I'll still ask him to belay me "normally" (no attempt of "soft catch") when belaying me on a trad line (unless it is obviously overhung, for which I'm too old, fat, and lazy these days). 

Patrik wrote:

Aha, this is very true. The publication with measured tests that I mentioned basically nails a grigri to a log. 

Yes, I tried to start my description with a "hard catch" (As I wrote: So for a hard catch, the force on the top piece of gear (and climber) is increasing from 0 to its maximum value when the climber "bottoms out") and then explain in a non-engineering fashion what would be needed to do to achieve a dynamic belay. Basically, when Alexz is belaying Old Lady H pulling a gnarly overhang. 

Trying to explain there are two different peak forces that are shifting in time and the sum is generating .... is probably going to lose most non-engineers around here. 

I still stick to my main point: A true dynamic belay attempting to significantly reduce the peak force on the top piece is considerably harder to do than the "soft catch" that sport climbers are asking for to keep them away from slamming into a wall. These are two very different tasks. Even if someone brags about being successful in the latter, I'll still ask him to belay me "normally" (no attempt of "soft catch") when belaying me on a trad line (unless it is obviously overhung, for which I'm too old, fat, and lazy these days). 

Understanding that those are all different, was the genesis of my question!

Soft catch for climber, soft catch to clear a roof or something, no choice soft catch from lighter belayer. All different than what would be needed to "save" a top piece, I think. Then, the hard catches, going the other way. "Hail Mary" plays to save a climbers ass. Or. Ignorantly delivered to the light old lady on a lead if Aleks can't haul it off the ground. Not happened yet to date, just an example.

I do grasp, that a soft catch solely for the sake of the top piece of gear, is the most difficult one to achieve, and the window is very narrow.

Still, it is an interesting question, to me, at least, even being just a duct tape engineer at best...

Rgold (and others on here) are quite aware that I'm that annoying kid who always had/has questions, but still won't just take your word for it, lol!

I will say, Jim Titt has some really readable research papers out there, very fun and interesting! 

Best, Helen

:-)

David Kerkeslager wrote:

I too generally respect Jim's opinions, but it's a bit unclear from that thread if Jim actually thinks screamers are useless. Luckily the man is here, perhaps you can clarify, Jim?

If my understanding of the physics is correct, the tearing screamer does dissipate energy. However, the screamer also allows the falling climber to build up more kinetic energy as they fall farther. This extra kinetic energy enters the rest of the system once the screamer has fully activated. Additionally, higher fall forces can cause the tearing of the stitching to dissippate less energy. If the extra distance fallen is long enough and the fall force high enough, the kinetic energy of the further fall will be greater than the energy dissipated by the screamer, resulting in higher forces on the rest of the system.

The engineering conclusion I'd draw from this is that if real-world falls are seeing an increase in force from using a screamer, screamers should be made with stronger stitching that dissipates more force over shorter distance as it tears. Additionally, it would be ideal for the screamer to be long enough that real-world falls can't fully activate the screamer.

The climbing-related conclusions I'd draw from this are to only use a screamer if there's a short (but difficult) distance to the next piece.

But I definitely don't think I've fully modeled this whole situation in my head so there might be things I'm missing.

They might be of some use in certain circumstances but I don´t own any or intend to if that helps!

Some years back I was doing something else an equipment manufacturer and the development technician was becoming increasingly frustrated having made and drop-tested screamers for weeks and as he put it "they don´t fucking work!" The problem was he was testing them too hard and so we progressively reduced the drop until they had some effect, at the subsequent product meeting it was decided they didn´t actually do any harm and the product description would include  "may" in any performance claim.

It is worth noting there is no performance test for screamers by the UIAA or CE/EN, the tests for via ferrrata screamers have shown that even under the strictly defined conditions they are tested to things can be deceptive leading to changes to  provide protection to lighter persons/children. Exactly why a 6kN screamer fails to deploy if a lighter person falls on it but allows them to be exposed to a higher impact than 6kN has not been clearly explained.

Via ferrata/fall protection screamers are relatively simple to model, the interaction between all the parts in a lead fall isn´t! The CAI tests are the only ones that attempt to show what happens when a belayer is included in the testing.

Patrik wrote:

Well, I can see that an industrial application company ( yatesgear.com/climbing/scre…) might try to "extend the truth" a little bit and sell gear that's really intended for "via ferrata" style work applications as being somewhat related to lead climbing.

But a reputable climbing company ( https://www.petzl.com/US/en/Sport/Carabiners-and-quickdraws/NITRO-3 ) is clearly advertising their products for lead climbing (download the "Technical notice" pdf to see it) and their stuff doesn't work?

Scary.

Of course they work, it´s a sling certified to EN566. Whether it has some other benefits isn´t clear, a table showing a 50% "gain" is completely inexplicable. No manufacturer has yet published tests using "real life" scenarios to prove or disprove the CAI  results so these are the only evidence for the true effectiveness of screamers.

David Kerkeslager wrote:If my understanding of the physics is correct, the tearing screamer does dissipate energy. However, the screamer also allows the falling climber to build up more kinetic energy as they fall farther. This extra kinetic energy enters the rest of the system once the screamer has fully activated. Additionally, higher fall forces can cause the tearing of the stitching to dissipate less energy. If the extra distance fallen is long enough and the fall force high enough, the kinetic energy of the further fall will be greater than the energy dissipated by the screamer, resulting in higher forces on the rest of the system.

If you want to apply conservation of energy, it's much better to think of the unstitched screamer adding to the potential energy lost by the falling climber.  The lost potential energy is easily quantified, at least in the case of full deployment, whereas knowing the kinetic energy as a function of time is tantamount to solving the problem. 

Jim Titt wrote:

They might be of some use in certain circumstances but I don´t own any or intend to if that helps!

Some years back I was doing something else an equipment manufacturer and the development technician was becoming increasingly frustrated having made and drop-tested screamers for weeks and as he put it "they don´t fucking work!" The problem was he was testing them too hard and so we progressively reduced the drop until they had some effect, at the subsequent product meeting it was decided they didn´t actually do any harm and the product description would include  "may" in any performance claim.

It is worth noting there is no performance test for screamers by the UIAA or CE/EN, the tests for via ferrrata screamers have shown that even under the strictly defined conditions they are tested to things can be deceptive leading to changes to  provide protection to lighter persons/children. Exactly why a 6kN screamer fails to deploy if a lighter person falls on it but allows them to be exposed to a higher impact than 6kN has not been clearly explained.

Via ferrata/fall protection screamers are relatively simple to model, the interaction between all the parts in a lead fall isn´t! The CAI tests are the only ones that attempt to show what happens when a belayer is included in the testing.

Hm. So what you're saying is that there are data points not explained by existing models, so we must not have adequately modeled this yet? I guess then we don't have any way of knowing whether screamers work.

My main hope for getting a screamer was to be able to put it on small gear--not gear that's marginal due to sketchy placement, but gear that's marginal due to the rating of the gear such as well-placed white tricams or micro nuts. I guess that hope isn't realistic.

Patrik wrote:

My suggestion would be to ask the one you are belaying (preferrably before he falls). There are differing (sometimes strong and occasionally unfounded) personal preferences out there. While you're at it, you might as well ask them if they accept your ATC/grigri/cinch, if they would like you to use belay gloves, if it is fine (or preferred) that you tether to ground, and if they have an opinion on palm up vs palm down belaying. 

As belayers, we are truly a "slave" to the leader if the leader has strong opinions about certain styles. 

 The belayer is a teammate. Lets not spark any drama. Jokes eventually become points of arguments, and for those who can't control themselves, rage. 

A good belayer will be able to judge the proper amount of slack on the fly. Dynamic route? The climber needs slack. Many times, the rope has kept me tight against the wall when I jump on an overhang, because of numbnuts down on the ground. Or for a Redpoint attempt, anywhere, there should be some slack out, to have a head start on when the slack gets taken to clip pro. An inexperienced, tense belayer will wait until the rope gets pulled on, thus, short roping. A good belayer will identify a clipping stance and hand movement toward the knot. 

Now, people belaying a climber on high grades, with an ATC, ughhhh. Resetting the brake hand for every stroke of feeding slack slows you down SO much. And it seems like people aren't putting much thought into correcting this problem. I see a lot of climbers pulling on short slack, desperately trying to complete that clip. What I started doing is belaying almost identically to the style of a grigri. Brake hand stays stationary, slack hand pushes slack out. Problem solved. 

20 kN wrote:

Considering that many, many climbers have ripped gear even with soft catches, it's completely logical to reach the conclusion that at least in some instances hard catches have had a direct influence on pieces ripping.

 Actually, 98% of all ripped gear is due to shitty placements. 

Paul Hutton wrote:

Now, people belaying a climber on high grades, with an ATC, ughhhh. Resetting the brake hand for every stroke of feeding slack slows you down SO much. And it seems like people aren't putting much thought into correcting this problem. I see a lot of climbers pulling on short slack, desperately trying to complete that clip. What I started doing is belaying almost identically to the style of a grigri. Brake hand stays stationary, slack hand pushes slack out. Problem solved. 

Indeed!

We learn belaying with an ATC in the hand over hand method. Two hands on the break lead, hand over hand down the rope. Then the rope is blocked with the lowest hand and the other hand moves to the lead rope to pull out some slack. Very slow method! When I used a tunneling breakhand while the other was pulling out the lead rope at the same time, in the gym to prevent short roping a quickly moving climber, i got a strong reprimande from a staff member. 

But there was an article in “Berg und Steigen” one or two years ago describing the tunneling method to be actually safer. 

Tim Lutz wrote:

Well, as they say - your experience may vary. I am still trying to learn how to give 50lb lighter climber soft catches. 

Those soft catches are definitely easier when the climber is heavier than belayer.

"sport loops" ??    Dear lord, this sounds dangerous to me.  No thanks.  The climber should expect his belayer to have a hand on the brake, and that's about it.  The rest is kinda high maintenance gym-style crap in my book.   

Russ Keane wrote:

"sport loops" ??    Dear lord, this sounds dangerous to me.  No thanks.  The climber should expect his belayer to have a hand on the brake, and that's about it.  The rest is kinda high maintenance gym-style crap in my book.   

If you are ever looking for partners online, make sure you put this in your partner-finder profile, so someone looking for high-maintenance gym crap wouldn't accidentally say yes to you.