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USnavy


Dec 25, 2012, 9:40 PM
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Quick and dirty test: What happens during shockloading?
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Today I performed a quick, dirty and non-scientific test for a highline article I am writing, and I came across some results that may interest climbers. There is a lot of talk about how a short fall on a Dyneema sling can cause the sling to fail, but drop testing fabrics can be a bit abstract, and it can be hard to visualize what is actually going on within the sling during a fall. This quick and dirty test may help make it easier to visualize a shockloading scenario from the viewpoint of the sling.

In the photo below you can see a load cell connected to a bolt and to a 1” nylon webbing sling tied in a sliding X. Attached to the sling is a steel ring that weighs 12 lbs. I picked the ring up and dropped it 20” onto the cell.



Load weight: 12 lbs.
Fall factor: 1
Fall distance: 20”

Dynometer scan rate: 520Hz / 1.92ms per reading
Peak load: 457 lbf. / 2.03kN*
50 lbf to 50 lbf load duration: Approximately 24ms



*The scan rate of my dynometer was actually too slow, and so the dynometer was not able to capture the true peak. Therefore, the actual peak load of this fall is actually slightly higher than what the dyno measured. If you look closely at the graph you will notice that top of the peak is flat. The start and end points of the flat section of the peak is actually the duration between two individual samples!

To further emphasize the short duration of a static fall like what I tested, let us compare it to the graph below. The graph below represents three lead falls in a typical climbing scenario. The load cell was placed on the protection bolt.



The fall above had a duration of around 2,500ms which is obviously far longer than the 24ms the static fall drop test took.

In conclusion, this quick test, which involved a 20” fall of a 12 lb. steel weight, produced a peak load increase of over 3,800%. Although this test is not analogous of a typical climbing shockloading fall due to a lack of a fleshy mass, it still emphasizes how relatively short falls on static materials can produces insane peak loads. I suspect that if the load weighed 80kg, I would have broken the bolt in the ceiling and exceeded the weight limitation of my load cell.


JAB


Dec 27, 2012, 5:45 AM
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Re: [USnavy] Quick and dirty test: What happens during shockloading? [In reply to]
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OK, this is nice and everything, but really adds nothing we already didn't know. What would be much more interesting, is if you now did the same test on yourself, as in a real world scenario. I.e. put on harness, girth hitch sling to it, other end to bolt, and then drop the 20". Compare results.

Now everybody knows that the human body, harness, loose knots etc all help to reduce the load, but nobody can say by how much.


ObviousTroll


Dec 27, 2012, 6:08 AM
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JAB wrote:
OK, this is nice and everything, but really adds nothing we already didn't know. What would be much more interesting, is if you now did the same test on yourself, as in a real world scenario. I.e. put on harness, girth hitch sling to it, other end to bolt, and then drop the 20". Compare results.

Now everybody knows that the human body, harness, loose knots etc all help to reduce the load, but nobody can say by how much.

I triple doggy dare you.


acorneau


Dec 27, 2012, 6:19 AM
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ObviousTroll wrote:
JAB wrote:
OK, this is nice and everything, but really adds nothing we already didn't know. What would be much more interesting, is if you now did the same test on yourself, as in a real world scenario. I.e. put on harness, girth hitch sling to it, other end to bolt, and then drop the 20". Compare results.

Now everybody knows that the human body, harness, loose knots etc all help to reduce the load, but nobody can say by how much.



I triple doggy dare you.


I accidentally did this a long time ago when I was a snot-nosed kid new to climbing.

At the time the sliding-x was a very popular method of rigging a top rope. I thought if it was good enough for a TR then it was good enough for my anchoring tethers, so I put a locker on my harness and rigged a 4' Titan sling in a sliding-x with biners on each end.

I lead a sport climb and barely made it to the top, clipped the first biner on one hanger and the other was just a few inches short. As I stretched to clip the second bolt my arm holding me up gave out and I fell directly on the sling, roughly 24" worth.

It completely wrenched my back and hurt like a beyotch! I managed to get back up and finish up the rigging but the drop messed with my back the rest of the day.


patto


Dec 27, 2012, 7:45 AM
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And I bet that ceiling flexes alot more than solid rock!


PeteF


Dec 27, 2012, 1:33 PM
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Re: [USnavy] Quick and dirty test: What happens during shockloading? [In reply to]
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In reply to:
In conclusion, this quick test, which involved a 20” fall of a 12 lb. steel weight, produced a peak load increase of over 3,800%. Although this test is not analogous of a typical climbing shockloading fall due to a lack of a fleshy mass, it still emphasizes how relatively short falls on static materials can produces insane peak loads. I suspect that if the load weighed 80kg, I would have broken the bolt in the ceiling and exceeded the weight limitation of my load cell.

Thanks very much for going to the trouble of doing that and putting it up here. For those of us new to climbing it's a good reminder.

Since you have all the gear there handy, is there any chance of repeating the experiment with a comparison between otherwise identical components but one static while the other is dynamic? For example two different ropes. I would be interested to see the difference in results over a short drop like this.


Syd


Dec 28, 2012, 11:35 AM
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Re: [USnavy] Quick and dirty test: What happens during shockloading? [In reply to]
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The main peak load occurs over 85ms (that is, the width of the peak above the final base load). The most extreme part of the peak load happens in a shorter period. It is interesting to consider this in relation to active dynamic belaying. It is claimed that if the belayer jumps or steps or actively initiates a moves in some way, when a climber falls, he can reduce the peak loading on the climber. It takes an absolute minimum of 200ms for a person to react to some stimulus (such as hearing a yell "falling" or seeing a fall), and generally this time is much longer. Further time is then required for the belayer to flex in some way. To reduce the peak load on the climber, the belayer's jump would then have to be precisely synchronised with the 85ms peak load. To me, this seems almost impossible.

Any "dynamic" effect by the belayer is simply the belayer being lifted off the ground by the impact of the fall. It is virtually impossible for the belayer to actively contribute to any impact reduction.

Many people consider that dynamic belaying is an essential part of good belaying but actions other than allowing some rope slip through the belay device at the moment of impact and an indirect or semi direct belay, seem futile.


(This post was edited by Syd on Dec 28, 2012, 11:41 AM)


redlude97


Dec 28, 2012, 11:45 AM
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Re: [Syd] Quick and dirty test: What happens during shockloading? [In reply to]
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Syd wrote:
The main peak load occurs over 85ms (that is, the width of the peak above the final base load). The most extreme part of the peak load happens in a shorter period. It is interesting to consider this in relation to active dynamic belaying. It is claimed that if the belayer jumps or steps or actively initiates a moves in some way, when a climber falls, he can reduce the peak loading on the climber. It takes an absolute minimum of 200ms for a person to react to some stimulus (such as hearing a yell "falling" or seeing a fall), and generally this time is much longer. Further time is then required for the belayer to flex in some way. To reduce the peak load on the climber, the belayer's jump would then have to be precisely synchronised with the 85ms peak load. To me, this seems almost impossible.

Any "dynamic" effect by the belayer is simply the belayer being lifted off the ground by the impact of the fall. It is virtually impossible for the belayer to actively contribute to any impact reduction.

Many people consider that dynamic belaying is an essential part of good belaying but actions other than allowing some rope slip through the belay device at the moment of impact and an indirect or semi direct belay, seem futile.
You got it all wrong. First a dynamic rope spreads the peak load out farther. Second, to give a dynamic belay you just have to time your jump so that you are moving upwards at point the rope catches. you are in the air for 1-2 seconds which is pretty easy to time with the fall once you get used to it. Just wait until you just feel the rope tension and jump. It works. Period.


healyje


Dec 28, 2012, 1:16 PM
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Re: [USnavy] Quick and dirty test: What happens during shockloading? [In reply to]
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I see a balcony in that photo - surely you can come up with a more realistic test...


Syd


Dec 28, 2012, 2:26 PM
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Re: [redlude97] Quick and dirty test: What happens during shockloading? [In reply to]
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redlude97 wrote:

You got it all wrong. First a dynamic rope spreads the peak load out farther. Second, to give a dynamic belay you just have to time your jump so that you are moving upwards at point the rope catches. you are in the air for 1-2 seconds which is pretty easy to time with the fall once you get used to it. Just wait until you just feel the rope tension and jump. It works. Period.

You've totally missed the point. Try jumping off the ground and staying in the air for 1-2 seconds as you claim. A belayer is PULLED into the air.
Do you really think you can time your little jump accurately to 85 milli seconds ?


redlude97


Dec 28, 2012, 2:33 PM
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Re: [Syd] Quick and dirty test: What happens during shockloading? [In reply to]
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Syd wrote:
redlude97 wrote:

You got it all wrong. First a dynamic rope spreads the peak load out farther. Second, to give a dynamic belay you just have to time your jump so that you are moving upwards at point the rope catches. you are in the air for 1-2 seconds which is pretty easy to time with the fall once you get used to it. Just wait until you just feel the rope tension and jump. It works. Period.

You've totally missed the point. Try jumping off the ground and staying in the air for 1-2 seconds as you claim. A belayer is PULLED into the air.
Do you really think you can time your little jump accurately to 85 milli seconds ?
You don't get it. You don't have to be accurate to within milliseconds. The catch just has to occur while you are still moving up during your jump. You also aren't just guessing. You jump when you start to feel the tension.


(This post was edited by redlude97 on Dec 28, 2012, 2:43 PM)


petsfed


Dec 28, 2012, 3:54 PM
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Re: [USnavy] Quick and dirty test: What happens during shockloading? [In reply to]
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Shock loading is what we call sudden increase of load to the point that, in comparison to the scale of the entire event, it acts like a delta function in time. There's nothing fancy about that. Its just verbal short-hand. Moreover, because of the extremes that necessitate the delta-function approximation, the actual behavior of the system is not, strictly speaking, predictable.

You want to impress me with your greater understanding, then show me if your loading profile exhibits marked asymmetry, periodicity, or multiple peaks. Then, talk to me about cyclic loading and relaxation time.

As it stands, you've used more words than normal to express what's been known for better than 60 years by engineers around the world, some of which happen to be climbers.


dan2see


Dec 28, 2012, 8:22 PM
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To JAB and petsfed, here's two juicy Tongue Tongue
for your negative comments that belittle USNavy's demo.

To Syd and redlude97, here's two more juicy Tongue Tongue
for changing the subject from "static anchor" to "dynamic belay".

To USNavy, thanks for the demo. I like to see these experiments that verify, extend, or negate stuff everybody knows everything about.

This week-end I will be playing with anchors and belays. So I will keep your findings in focus, while I'm messing around with my gear, on the rocks, with my delicate body.


(This post was edited by dan2see on Dec 28, 2012, 8:23 PM)


JimTitt


Dec 28, 2012, 10:05 PM
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Syd wrote:
The main peak load occurs over 85ms (that is, the width of the peak above the final base load). The most extreme part of the peak load happens in a shorter period. It is interesting to consider this in relation to active dynamic belaying. It is claimed that if the belayer jumps or steps or actively initiates a moves in some way, when a climber falls, he can reduce the peak loading on the climber. It takes an absolute minimum of 200ms for a person to react to some stimulus (such as hearing a yell "falling" or seeing a fall), and generally this time is much longer. Further time is then required for the belayer to flex in some way. To reduce the peak load on the climber, the belayer's jump would then have to be precisely synchronised with the 85ms peak load. To me, this seems almost impossible.

Any "dynamic" effect by the belayer is simply the belayer being lifted off the ground by the impact of the fall. It is virtually impossible for the belayer to actively contribute to any impact reduction.

Many people consider that dynamic belaying is an essential part of good belaying but actions other than allowing some rope slip through the belay device at the moment of impact and an indirect or semi direct belay, seem futile.

Even in the shorter falls used in lab experiments which are the only ones we get full data for the time from initially tensioning the rope to the peak force is substantially longer than you are talking about, around 200ms is probably reasonable. From the point of falling where a reasonably alert belayer has clues to prime his movement you´d have about 400ms.
If you look at US´s lower graph (which is a longer, lower FF)you´ll see the belayer had about 500ms from tension to peak and probably over a second if he saw the fall.
If the time from tension to peak was a short as you think then the impact force would be horrific!


USnavy


Dec 28, 2012, 11:51 PM
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Re: [petsfed] Quick and dirty test: What happens during shockloading? [In reply to]
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Syd wrote:
The main peak load occurs over 85ms (that is, the width of the peak above the final base load).
No it does not, look again. From 50lbf to 50lbf the load duration is 24ms.


petsfed


Dec 29, 2012, 10:33 AM
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Re: [dan2see] Quick and dirty test: What happens during shockloading? [In reply to]
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dan2see wrote:
To JAB and petsfed, here's two juicy Tongue Tongue
for your negative comments that belittle USNavy's demo.

Dan, with respect, I don't see how USNavy's demo is at all useful. If you want a useful illustration of shock loading, look at a hammer and nail. If you swing the hammer, you drive the nail. If you apply the same impulse (that is, change in momentum for the hammer over some distance) over a longer time, you don't drive the nail.

That's shock-loading, and perfectly illustrates why we need to worry about it. That said, its not clear how much of an issue that is with a dynamic rope, so these tests are not at all informative.


Syd


Dec 29, 2012, 12:19 PM
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JimTitt wrote:


Even in the shorter falls used in lab experiments which are the only ones we get full data for the time from initially tensioning the rope to the peak force is substantially longer than you are talking about, around 200ms is probably reasonable.

Based on ? I have seen a graph but I'm damned if I can find it.

In reply to:
If you look at US´s lower graph (which is a longer, lower FF)you´ll see the belayer had about 500ms from tension to peak and probably over a second if he saw the fall.

In fall of 20 to 30 ft, the belayer has about 1300 ms from fall to peak. The point is the time to react and how to precisely synchronise his jump with the peak.

As USNavy says, you can define the peak as an even shorter period.

Try standing on a flat surface in belay stance and as quickly as possible, jump as high as possible. You might raise your CG by a couple of inches. That is, by a dynamic belay jump, you might be able to reduce the energy of the climber's fall by perhaps 1% or so ... if you time your jump precisely to the millisecond.

Belayers are better off forgetting about jumping to give an active dynamic belay, and locking off the rope correctly and focussing on not tripping or hitting the wall if on an indirect belay.


jt512


Dec 29, 2012, 3:09 PM
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Syd wrote:
JimTitt wrote:


Even in the shorter falls used in lab experiments which are the only ones we get full data for the time from initially tensioning the rope to the peak force is substantially longer than you are talking about, around 200ms is probably reasonable.

Based on ? I have seen a graph but I'm damned if I can find it.

In reply to:
If you look at US´s lower graph (which is a longer, lower FF)you´ll see the belayer had about 500ms from tension to peak and probably over a second if he saw the fall.

In fall of 20 to 30 ft, the belayer has about 1300 ms from fall to peak. The point is the time to react and how to precisely synchronise his jump with the peak.

As USNavy says, you can define the peak as an even shorter period.

Try standing on a flat surface in belay stance and as quickly as possible, jump as high as possible. You might raise your CG by a couple of inches. That is, by a dynamic belay jump, you might be able to reduce the energy of the climber's fall by perhaps 1% or so ... if you time your jump precisely to the millisecond.

Belayers are better off forgetting about jumping to give an active dynamic belay, and locking off the rope correctly and focussing on not tripping or hitting the wall if on an indirect belay.

You don't know what you're talking about. But you're right about one thing: if you're too uncoordinated to time the jump properly, you're better off just standing there and locking off, since jumping too early results in a harder catch than if you just stand there like an idiot and lock off.

Better yet, offer to let someone who knows what they're doing belay.

Jay


(This post was edited by jt512 on Dec 29, 2012, 3:10 PM)


Syd


Dec 29, 2012, 6:26 PM
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jt512 wrote:

But you're right about one thing: if you're too uncoordinated to time the jump properly, you're better off just standing there and locking off, since jumping too early results in a harder catch than if you just stand there like an idiot and lock off.
Jay

Another fellow conned by the dynamic belay myth. How high do you think you can you jump while belaying ... 4 inches maybe 6 ? Or do you think you can equal the athlete maximum 28 inch vertical leap? I'm talking about actually jumping your CG up instantaneously from a resting, unprepared stance. How does your 4 to 6 inches, compare to a typical fall of 20-30 ft or more ? That is, there is at least 40 to 90 TIMES AS MUCH energy in the fall as your pathetic bunny hop !
... and you think you can time your little bunny hop accurately to a small fraction of a second !? A mis-timing of 200 milliseconds and you add to the impact ... not that the falling climber would notice your tiny bunny hops. The falling climber will rip you off the ground as the rope tensions and you will be fooled into thinking you have done wonders.
You are dreaming if you think it helps.


shotwell


Dec 29, 2012, 7:28 PM
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Syd wrote:
jt512 wrote:

But you're right about one thing: if you're too uncoordinated to time the jump properly, you're better off just standing there and locking off, since jumping too early results in a harder catch than if you just stand there like an idiot and lock off.
Jay

Another fellow conned by the dynamic belay myth. How high do you think you can you jump while belaying ... 4 inches maybe 6 ? Or do you think you can equal the athlete maximum 28 inch vertical leap? I'm talking about actually jumping your CG up instantaneously from a resting, unprepared stance. How does your 4 to 6 inches, compare to a typical fall of 20-30 ft or more ? That is, there is at least 40 to 90 TIMES AS MUCH energy in the fall as your pathetic bunny hop !
... and you think you can time your little bunny hop accurately to a small fraction of a second !? A mis-timing of 200 milliseconds and you add to the impact ... not that the falling climber would notice your tiny bunny hops. The falling climber will rip you off the ground as the rope tensions and you will be fooled into thinking you have done wonders.
You are dreaming if you think it helps.

Remind me to NEVER let you belay me.


jt512


Dec 29, 2012, 7:34 PM
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Syd wrote:
jt512 wrote:

But you're right about one thing: if you're too uncoordinated to time the jump properly, you're better off just standing there and locking off, since jumping too early results in a harder catch than if you just stand there like an idiot and lock off.
Jay

Another fellow conned by the dynamic belay myth. How high do you think you can you jump while belaying ... 4 inches maybe 6 ?.

You're arguing theory in the face of decisive contrary empirical evidence, and you're arguing with people who on a day in and day out basis continue to generate that evidence. When an overwhelming amount of data contradicts your theory, then your theory is wrong. The zillions of real climbers who give and receive well-executed dynamic belays every time we're out climbing can assure you that dynamic belaying is no myth. In fact, it is a relative simple skill to master, and a vitally important one. I'm about a decade and half past trying to convince the minority of climbers who cling to the paradigm of dynamic belay denial. I simply refuse to climb with deniers, as do many of my partners.

Shut up and learn how to belay already.

Jay


dan2see


Dec 29, 2012, 8:22 PM
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Re: [jt512] Quick and dirty test: What happens during shockloading? [In reply to]
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shotwell wrote:
... Remind me to NEVER let you belay me.

jt512 wrote:
... Shut up and learn how to belay already.

Oh yeah? Well your mother wears army pants! Tongue
Both of you! Tongue

The thing is, it's fun to be more right than the other guy. But it's another thing entirely to figure out how things work, and what you should do about it.

For myself, the only "rule" for my belayer is "Never let go of the break brake strand".

Petzl (I think) once had a page of advice, related to lead techniques. In the paragraph about anchors, their advice was "... Clip your sling to the anchor, sit in your harness, and ..."

So you guys, you don't have to be more scientific, or more experienced, than the OP. But it's silly to argue about how to belay.

---o---o---

Some time ago, I asked a couple of friends about that short phrase "sit in your harness", but nobody had noticed it. One guy said "Well that's what I always do" and another said "Huh? What?" but nobody had a reason.

Although plenty of folks I climb with today know that a short fall off your anchor produces a high fall-factor that can injure you. These same guys will get very nervous if anybody climbs above the top anchor.

(Edit ...)
Oops not "today"! Everybody I know is skiing, or climbing ice today. Well I never learned to ski, and I'm staying off the ice-climbs for this winter.
But I'm still messing around on snow and rock and scree and other silliness.


(This post was edited by dan2see on Dec 29, 2012, 9:36 PM)


patto


Dec 29, 2012, 9:04 PM
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Syd wrote:
The main peak load occurs over 85ms (that is, the width of the peak above the final base load). The most extreme part of the peak load happens in a shorter period. It is interesting to consider this in relation to active dynamic belaying. It is claimed that if the belayer jumps or steps or actively initiates a moves in some way, when a climber falls, he can reduce the peak loading on the climber. It takes an absolute minimum of 200ms for a person to react to some stimulus (such as hearing a yell "falling" or seeing a fall), and generally this time is much longer. Further time is then required for the belayer to flex in some way. To reduce the peak load on the climber, the belayer's jump would then have to be precisely synchronised with the 85ms peak load. To me, this seems almost impossible.

Any "dynamic" effect by the belayer is simply the belayer being lifted off the ground by the impact of the fall. It is virtually impossible for the belayer to actively contribute to any impact reduction.

Many people consider that dynamic belaying is an essential part of good belaying but actions other than allowing some rope slip through the belay device at the moment of impact and an indirect or semi direct belay, seem futile.

I completely agree with this.

And I believe there has been other good research to support this. Dynamic belaying was found produce only very minor reductions in peak load. If you are doing it to make you and you partner more comfortable on repeated sport climbing falls then I don't see a problem. In steep over hangs more slack or dynamic belays can avoid ankle damaging pendulums.

If you think it is an essential part of safety in TRAD climbing then you are misguided. The difference between a grigri and a ATC is far bigger. But unless you are frequently leading very tiny pieces then I don't believe dynamic belays are important. (Even when I've lead X rated climbes with RPs and ultra micro cams I've never felt the need for a dynamic belay. Personally I want a reliable catch and in the event of piece failure a reliable FF2 preventative measures.)


Certainly amongst MY local TRAD community dynamic belays are never emphasised.


dan2see


Dec 29, 2012, 9:39 PM
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Re: [patto] Quick and dirty test: What happens during shockloading? [In reply to]
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patto wrote:
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Certainly amongst MY local TRAD community dynamic belays are never emphasised.

And amongst my local sport community, I've never seen anyone do a dynamic belay.


bearbreeder


Dec 29, 2012, 10:10 PM
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Re: [shotwell] Quick and dirty test: What happens during shockloading? [In reply to]
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Dynamic belaying

Some think it is difficult to belay dynamically with the GRIGRI. But it is the belayer, not the belay device, that plays the primary role in dynamic belaying.

The key to dynamic belaying: step or make a small jump forward when the climber falls. We also stress that dynamic belaying does not mean keeping 3-4 m of slack in the climber’s side of the rope: this does not reduce the force of a fall. In addition, in the case where the climber has not gained enough height, it increases the risk of a ground fall.

In any case, it is necessary to be attentive and vigilant while belaying, so that potential falls can be anticipated. Remember that where there is a risk of a ground fall, or striking a ledge, a dynamic belay should not be used.

It takes practice to master dynamic belaying. To practice, start with falls sufficiently high relative to the ground (for example, when the climber is nearing the end of a pitch)


http://www.petzl.com/...erience#GE-dynamique


its that simple folks Wink

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