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.

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.

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.

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 ?

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.

The main peak load occurs over 85ms (that is, the width of the peak above the final base load).

To JAB and petsfed, here's two juicy
for your negative comments that belittle USNavy's demo.

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.

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.

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


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.

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.

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

... Remind me to NEVER let you belay me.

... Shut up and learn how to belay already.

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.

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