The French take on belay anchors and technique (ENSA video)

King Tut wrote:

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What the Climbing Team needs to understand is that there is a difference between a softer catch for the leader at the price of higher load on the protection vs lower load on crappy gear. They need to then decide the best way to belay.

Otherwise we should place an anchor at the base of every sport climb but we don't. We greatly prefer a softer catch for the leader when protection is reliable, or we may or may not if there is danger from a ledge etc.

There is no one size fits all answer.

  

Umm??  A softer catch puts a higher load on the protection??? 

When the gear is solid, we want a soft catch?  When the gear is less reliable we don't want a soft catch?  

Want to rethink that?

Greg D wrote:

Umm??  A softer catch puts a higher load on the protection??? 

When the gear is solid, we want a soft catch?  When the gear is less reliable we don't want a soft catch?  

Want to rethink that?

Sorry, got my physics messed up, I'll rethink and repost.

*edited the above, got all mixed up :(.

brenta wrote:

The explanation is on page 6: 

L’assureur, entraîné par le chuteur prend de la vitesse, donc de l’énergie cinétique. Dès quel’assureur  ne  peut  plus  bouger  le  relais  est  soumis  aux deux forces d’arrêt cumulées du chuteur et de l’assureur. L’assureur est  stoppé par son système d’autoassurage qui correspond à une chute sur une longe, sans assurage dynamique.

which means: The belayer, dragged by the faller, gains speed and hence kinetic energy.  As soon as the belayer can no longer move, the belay anchor is subjected to the cumulative arrest forces of faller and belayer.  The belayer is stopped by his attachment to the belay anchor, which corresponds to a fall on a sling, without dynamic belay.

This might explain the shape of the curve in the case of the reverso being on the belayer, but it does not in my mind explain why the force on the anchor is less with the direct belay, which although there would be no belayer to stop, there would not be raising of the belayer against gravity to reduce the kinetic energy. To me the proof would be if the rope had been tied to the anchor, then tied to the belayer (maybe this experiment is in the report and if so, rgold might well have spotted it), as it is I don't think we can know that in the one case presented more slack was not passed through the reverso when playing of the anchor.

Leaving that to one side, we all know that most of the time the belayer is not lifted far enough up to apply any force to the anchor - so the result is not a general one, and is the opposite of what most happens, or I would be permanently covered in belay bruises. And this is what somewhat gets my goat about the video (some of the others in the series are excellent): The experiments are not repeated with the same settings, let alone repeating with a wider range of angles, distances etc.  

David Coley wrote:

This might explain the shape of the curve in the case of the reverso being on the belayer, but it does not in my mind explain why the force on the anchor is less with the direct belay...

The key part of the explanation is "fall on a sling".  The belayer's attachment to the anchor (in the experiment) is far less stretchy than the climbing rope, so it can take a lot of force to stop the belayer's motion (even if the belayer is moving much slower than the climber).

I agree the video has a big problem with ignoring (not discussing and not reporting) variables that obviously affect the published results.

David Coley wrote:

This might explain the shape of the curve in the case of the reverso being on the belayer, but it does not in my mind explain why the force on the anchor is less with the direct belay, which although there would be no belayer to stop, there would not be raising of the belayer against gravity to reduce the kinetic energy. To me the proof would be if the rope had been tied to the anchor, then tied to the belayer (maybe this experiment is in the report and if so, rgold might well have spotted it), as it is I don't think we can know that in the one case presented more slack was not passed through the reverso when playing of the anchor.

Leaving that to one side, we all know that most of the time the belayer is not lifted far enough up to apply any force to the anchor - so the result is not a general one, and is the opposite of what most happens, or I would be permanently covered in belay bruises. And this is what somewhat gets my goat about the video (some of the others in the series are excellent): The experiments are not repeated with the same settings, let alone repeating with a wider range of angles, distances etc.  

Allow me to go back to the funkness device analogy, which works as follows: the belay anchor corresponds to the piton to be "funked out;" the belayer corresponds to the hammer; and the sling that tethers the belayer to the anchor corresponds to the funkness device.

Most climbing hammers have a mass of less than 1 kg.  Their kinetic energy when swung is unlikely to exceed 50 J.  Yet, they can apply forces of about 10 kN to a piton.  Hence it should come as no surprise that the belayer's sudden arrest when the sling goes taut may put a lot of force on the belay anchor.

But, one may argue, how do we know that this effect is important.  It may well be that the lower force on the anchor in case of direct belay is due to increased rope slippage.  I would counter that the ENSA people have high-speed footage and recordings of the dynamometer readings.  By matching footage to forces, they were able to determine that the peak force on the belay anchor occurs when the belayer's attachment goes taut.

It is clear that an experiment may be set up in which belayers who are belaying off their harnesses are not swept off their feet and the force on the belay anchor remains null. However, the ENSA people are careful in stating their assumptions in the summary of the article:

Lorsque la corde entre le relais et le point de renvoi ne subit aucun frottement, si le premier point est désaxé ou lors d’une chute de grande hauteur, l’assureur est violemment projeté contre la paroi par un mouvement de rotation autour du point d’attache de sa longe.

That is, "When the rope between the belay anchor and the runner is not subject to friction, if the first piece is not aligned or when the fall is from great height, the belayer is slammed against the wall by a rotation about the attachment point of his/her tether."

No blanket statement is made about the forces on anchors in all cases.  The authors of the study were themselves surprised by the fact that the force on the anchor may be higher when belaying from the harness, and this thread confirms that they were not alone to be surprised.  (I found their observations interesting and their explanation convincing.) Their main concern, though, is with the belayer getting hurt and possibly letting go of the rope.

We always want to see one more experiment performed, especially the one that would confirm our point of view, but if they had presented experiments showing that there are times--for instance, if there's plenty of rope drag--when the belayer hardly notices that the leader has fallen, wouldn't they be criticized for belaboring the obvious?

The video perhaps tries to cram too much into eight minutes, but taken together with the report, promotes an interesting debate.  Thanks to rgold for bringing it to our attention.

brenta wrote:

......................................The video perhaps tries to cram too much into eight minutes, but taken together with the report, promotes an interesting debate.  Thanks to rgold for bringing it to our attention.

Thanks, I agree with much of what you say, and think I just about understand the physics, but I still maintain that even though the analogy is good at explaining the shape of the curve and the case of the indirect belay,  it is the last step when this result is compared with the direct belay that concerns me - the video shows considerable slippage, more than I would suggest is normal. 

For some watchers, i.e. many of the posters on this thread the video provides an interesting starting point and a great way of opening a debate - all good.

But, few will read the report, so the video might be taken at face value and possibly being a definite conclusion. Its failures, such as showing footage of using a reverso (not a munter, as the text mentions) without a discussion of the possibly fatal fall that might occur if a redirect is not used before the first piece is clipped, or a discussion about having to site the belayer well below the anchor (often difficult), or whether this needs a re-think of the structuring of trad belays to take upward pulls (remember, it the anchor rips with an indirect one still hopefully has the reverso and brake strand in the braking position, with a direct this may well not be so), or that maybe this only about bolted or pegged anchors (which to be honest is where it came from in the Eastern Alps) makes the video a possibly dangerous object. I know people in my climbing club who have taken this video as conclusive and think we should consider changing practice. 

The other videos in the series are just so much better.

David Coley wrote:

Hi Phil, as rgold points out, I was not questioning whether a fall could be held, but how one takes in and gives slack efficiently, and without letting go of either rope. Out of interest, when you have done it, did you have two lockers with a munter on each, or one big locker, with one munter adjacent to the other.

I have no idea if you're still interested, but I was being belayed on a big locker each munter adjacent to each other. I took a big fall on it when a foot broke. I was definitely concerned when I saw my belayer wanting to set it up like that, but he was a good friend of mine that has done a lot of alpine in the dolomites, and the alps so I trusted him.

One thing the videos clarify is what can happen to the belayer when there is very little friction in the system, a condition that is fortunately uncommon in most trad climbing situations.  However, I've had the misfortune of catching some very low-friction falls on real rock and can confirm that the belayer is violently lifted and smacked into the wall.  After two such falls, I was a bloody mess from "road rash" as the wall above me was a touch under vertical, whereas the leader, who was falling into space, had nary a scratch.

One thing that came over well I thought in that last video was that if the Jesus piece is one of the anchor pieces it should be unclipped once the next piece is clipped (to reduce the speed you hit the wall).