More on...Belaying Leader off of Anchor, Two Good Bolts (A French technique)

I am pretty sure the issue with increased forces on the anchor and the top piece of gear are related to the acceleration of the belayer.  In particular the belayer is accelerated by the failing climber and then suddenly stopped by his connection to the belay (tether or rope).   In some sense you are doubling the mass of the leader by adding the belayers mass when the belayer come to the end of the tether.   So much depends upon the length of the tether and the force of the fall that I think it is very hard to predict what will actually happen in any given scenario.   But I think it is likely that you can create a scenario which increases the forces on the system above what those forces would be if you belayed off the anchor with any device.  Likewise I think with a long enough tether or no tether you can reduce the ultimate load (a typical sport climbing soft belay).    

As usual, rgold offers the definitive response. I've been reading on this technique for about 8 years, have practiced it in the field quite a bit, and have even done some drop testing on it, and I agree with basically everything he's stated.

I'll add that if there is still significant concern about an ABD for the belayer, the fixed-point aka direct belay can be hybridized with a traditional belay off the harness. Simply rig an ABD on the harness as normal with sufficient slack that the leader can get to the "good" pro, then belay with a fixed-point belay in front of this. Once the leader has clipped the requisite protection, simply pop the munter hitch out of the rope and belay as normal with an ABD on the harness.

But for real, if using a fixed-point belay:
1. Do NOT put an ABD on the anchor
2. Wear glvoes

Rich! "To reference another thread"....ha, the belay escape, indeed, heads up, you'll start another war!

Seriously, I'd say Derek D has probably done as much work on this topic (in terms of testing and real-world application) as anybody in the US, so listen up!

And Derek--clarify, it was you who showed me the little orange box at the end of the ENSA PDF describing how the belayer intentionally lets rope slip thru the Munter ... just geeked out for a sec found it:

"Nous avons obtenu la force de choc la plus faible en positionnant le système de freinage sur le relais et en laissant glisser la corde en augmentant le freinage progressivement. Cette méthode est difficile à exécuter et à réserver à des grimpeurs experts. Lorsque cela est possible (large vire) la méthode la plus simple est de dynamiser en déplaçant l’assureur. (figure 22). Si l’assureur est vaché au relais, la méthode qui génère les forces les plus faibles sur le point de renvoi est de positionner le système de freinage directement sur le relais.  C’est aussi la méthode la plus confortable pour l’assureur."

Link and above text appears on pg. 15 of the PDF: http://ensa.sports.gouv.fr/images/ENSA/recherche/laboratoire_essais/relais2017.pdf

One thing---to echo Derek and Rich's admonitions---the direct belay is not to be used with an ABD (GriGri, MegaJul, Pilot, etc). Edelrid just came out with the GigaJul which allows you to switch to non-ABD mode (kind of a cool feature if you're into this). Gloves mandatory.

Munter has worked for me and is less jangly than the plaquette, I think. I had a 100-lb kid that I would take out climbing (he's not bigger than me and on the national team for ice/mixed--punk kid!) and when he wanted to climb a bit harder, I had him direct-belay me off a Munter. Took him a single pitch to learn....super simple!

climber pat wrote: I am pretty sure the issue with increased forces on the anchor and the top piece of gear are related to the acceleration of the belayer.  In particular the belayer is accelerated by the failing climber and then suddenly stopped by his connection to the belay (tether or rope).   In some sense you are doubling the mass of the leader by adding the belayers mass when the belayer come to the end of the tether.   So much depends upon the length of the tether and the force of the fall that I think it is very hard to predict what will actually happen in any given scenario.   But I think it is likely that you can create a scenario which increases the forces on the system above what those forces would be if you belayed off the anchor with any device.  Likewise I think with a long enough tether or no tether you can reduce the ultimate load (a typical sport climbing soft belay).    

I believe the weight of the belayer "goes onto" (i.e. is added to) the top piece as soon as he/she starts to hold the falling climber (whether a leader, or a climber being top roped), and doesn't have to wait for any "sudden stop by his connection to the belay (tether or rope)" .  At least that was what I learned in physics class: If 150lbs downward force (climber) is hanging from a point and is balanced by another 150 lbs (force exerted by belayer to "hold" said climber) then there's 300 lbs on the "point".  

Robert Hall wrote:

I believe the weight of the belayer "goes onto" (i.e. is added to) the top piece as soon as he/she starts to hold the falling climber (whether a leader, or a climber being top roped), and doesn't have to wait for any "sudden stop by his connection to the belay (tether or rope)" .  At least that was what I learned in physics class: If 150lbs downward force (climber) is hanging from a point and is balanced by another 150 lbs (force exerted by belayer to "hold" said climber) then there's 300 lbs on the "point".  

You are right about the initial 150 lbs but the velocity of the belayer when he hits the end of tether is a much greater contributor to the force on the belay and top piece,   Your physics class just mimicked the soft sport belay by not tying the belayer on a leash.  f = ma and a is pretty high when you are stopped by the leash if you are moving at any speed.

Robert Hall wrote:

I believe the weight of the belayer "goes onto" (i.e. is added to) the top piece as soon as he/she starts to hold the falling climber (whether a leader, or a climber being top roped), and doesn't have to wait for any "sudden stop by his connection to the belay (tether or rope)" .  At least that was what I learned in physics class: If 150lbs downward force (climber) is hanging from a point and is balanced by another 150 lbs (force exerted by belayer to "hold" said climber) then there's 300 lbs on the "point".  

Let me try to me a little more clear about what I think happens.  

The leader take a big fall and generates lots of kinetic energy, finally coming to the end of the rope.  If the belayer is untethered, the belayer is accelerated upwards applying his weight + the force of his acceleration to the system.  This is more than his 150 lbs rather 150 lbs + 150 * acceleration.  The acceleration is initially 'high' when the force initially is transferred to the belayer.  The acceleration of the belayer slows as the energy is absorbed.  

Imagine if the belayer is tethered to the anchor with just the right length to stop him when he is traveling upward at the maximum his speed.  Stopping the belayer at this point is like the anchor is holding two climbers falling whatever distance corresponds to that speed.  And one of the climbers is on a very short piece of rope or a static sling so his deceleration can be quite severe.  We all know that you do not have to fall very far (accelerate much) to apply a huge load on an anchor with static sling.  It this case the belayer is accelerated upward by the force of holding the fall rather than downwards by gravity.

If you are belaying off the anchor then you never have the mass of the belayer accelerated and then stopped by the achor.    

I am still not satisfied with the explanation but I hope it helps. 

Subtract from this the kN of clove hitches, knots tightening and dissipation of rope thru top carabiner (as heat)....complicated, no?! Chauvin and I tried to dip our toes into discussing this when discussing FF2s and strategies for mitigation....but the physics get too complicated too quickly....and then of course different ropes/materials/carabiners all make the equation really really complicated. Interesting discussion, though, for folks who can actually formulate reasonable explanations/educated guesses about stuff....(I can't!)....

Robert Hall wrote: a 160 lb leader falling 10 ft generates 1600 ft-lbs of force.

Ft-lbs isn't a unit of force, it's a unit of energy.  You cannot determine the force a falling climber exerts on the rope/system in this way, without more complicated details about rate of deceleration or specific properties of the rope and knowledge of the rope and protection length and arrangement.

Cant speak about the physics. I just think that the length of rope out is critical to understand why the Munter directly on the anchor is prefered. If belaying off the harness, redirecting the rope through the anchor with only a few meters of rope out there is not much dynamic material to soften the fall, worsened by the pulley effect, the latter also allowing less slippage. Both the anchor and belayer experience high forces.
Even so, Both the Italian (CAI) and German (DAV) alpine clubs recommend placing a protection point not further than 3 meters from the anchor when belaying with a munter directly off the snchor to avoid excesive forces in case of fall.
Also, speaking of fall factors only makes sense for a braking system that does not allow slippage: "blocked rope regime". this could be an ABD, a Munter flipped to take in slack, high friction or bends at carabiners (high drag).

I think all of us would recommend placing solid gear soon and frequently after the belay....there's some CAI testing out there, too, but i don't have links........

climber pat wrote: I am pretty sure the issue with increased forces on the anchor and the top piece of gear are related to the acceleration of the belayer.  In particular the belayer is accelerated by the failing climber and then suddenly stopped by his connection to the belay (tether or rope).   In some sense you are doubling the mass of the leader by adding the belayers mass when the belayer come to the end of the tether...

With you about forces on the anchor.

Re forces on the top piece - I don't think the belayer's mass favors a direct anchor belay.  In fact, the easiest case in support of direct anchor belay is when the belayer's mass is 0 - in this case all the belayer does is increase the fall factor by adding pointless slack to the system.

yes, I know Ft-lbs is energy, but that's because lbs is FORCE, not weight, and that's an issue with the "English" system of weights and measures.

That being said, I have caught 160 lbs (aka the force 7.2 stones excerts, I think, at sea level but maybe in London or Greenwich  ) falling totally free for 10 feet.  It's a bitch , in whatever measurement system you want to measure it.  Once it totally flipped me upside down (this was when we did "hip" belays), yet because I was tied in behind I held the "falling climber". (which in this particular instance was 160 lbs of sand)

 The point I was trying to make is that "once-upon-a-time" back in the "old days" it was taught to tie in behind you (at least a secondary tie-in) so that you wouldn't be pulled (smashed) into the rock (gym wall) in front of you and that sometime in the past 25 years this has fallen into dis-use / i.e. not-trained.  I wonder why and what was the rational.  People wonder why they are pulled (smashed) into the rock face catching a fall, and then sometimes even "drop" the falling leader.

Robert Hall wrote: Kyle- yes, I know Ft-lbs is energy,

That doesn't appear to be the case, since you specifically said ft-lbs was force: "generates 1600 ft-lbs of force"

 but that's because lbs is FORCE, not weight, and that's an issue with the "English" system of weights and measures.

Weight and force use the same unit.  Pounds-force (lbf) is a unit of weight or force, and Pounds-mass (lbm) is a unit of mass.

Regardless of the awkward units, you attempted to multiply weight (or maybe mass, it's unclear) by fall distance and equate that with force.  You can't do that, as it's not the correct units (regardless of whether you use weight or mass), AND it's not sufficient information to determine the force exerted.

It would be interesting to see a real-time plot the load cell data scrolling under the videos.  That way it would be easy to correlate the force reactions and peaks with what is actually happening.  

OK Kyle, there's no need to carry this on further.  You are correct, although I am sure that if you ask 1000 people whose first language is English how much they weigh I'm sure 998  would answer XXX lbs, and maybe 1 would say "Pounds Mass", and maybe 1 XX kgs.

The point is that a belayer can't expect to catch a falling leader (regardless of how much they weigh, lets say 80 kg)  just standing on the ground (or worse, on a belay ledge) without be pulled in the direction of the force generated by the falling mass.  This principle used to be taught, if not even "rammed down" the novice climber's/belayer's  throat.  It not longer is, and I don't know why, and honestly would like to know.

coppolillo wrote: I think all of us would recommend placing solid gear soon and frequently after the belay....there's some CAI testing out there, too, but i don't have links........

the point is that the fixed-point munter makes up for the lower stretch of the short length of rope. But the tests show that 3m above is the limit for manageable loads.

It accomplishes this by allowing controlled slippage and braking in any direction

Robert Hall wrote: This principle used to be taught, if not even "rammed down" the novice climber's/belayer's  throat.  It not longer is, and I don't know why, and honestly would like to know.

Yes it is.

Even gym lead classes teach this.

Then why does one almost never see it being done on climbs?

Robert Hall wrote: OK Kyle, there's no need to carry this on further.  You are correct, although I am sure that if you ask 1000 people whose first language is English how much they weigh I'm sure 998  would answer XXX lbs, and maybe 1 would say "Pounds Mass", and maybe 1 XX kgs.

Of course they would, because XXX lbs is the correct response to a question about weight.

I think maybe we got crossed up in communication here somewhere?  I am making two statements:

• Ft-lbs is not a unit of force
• You cannot determine the amount of force exerted on the system by multiplying climber weight by fall distance

Beyond that, I don't think continuing to debate the nuances of odd American units is of much value.

Robert Hall wrote: Then why does one almost never see it being done on climbs?

I can't answer to the back tie thing that you're talking about. I don't do it and don't have problems, but I also don't hip belay.

For the people that ignore pull direction, they probably don't pay attention for the same reason they don't wear helmets, take their brake hand off, forget double checks, blah blah blah blah blah: they're human.