Ok-- what am I missing or screwed up?

I think the real point is that a static (semi) fall of a few inches, as the sliding -x slides to the limiting knot, generates negligible force.

belayers body absorbing some energy

Thanks to John for initiating some testing to help dispell some of the myths.

So I can take from that you make no distinction about the use of the anchor relative to any reality of shock loading?

Also, the notion that an initial load, if it blows out one arm or a sliding x, will then quickly multiply to a higher weight when it drops onto the next arm--be it 4 inches or 1 foot--is something not happening in the actual drop tests. And these tests have load capturing devices accurate to one kilo.

Ok, I'm confused--- if you have two anchors, each joined together with a sling and say a 40 degree angle between them, then they each share a part of the initial load. Correct? How is it then that if one of those fails that the other anchor doesn't take the full load plus some for the initial shockloading part? I'm not questioning the results of the tests, just questioning if I'm understanding it correctly..

-J

Ok-- what am I missing or screwed up?

Sorry--- what I meant by the elongation of the rope is the initial fall causes a larger elongation than a soon after second fall-- ie the rope becomes stretched, doesn't have time to recover and won't stretch as much the second time--- hence a higher shockload on the remaining anchor.

the six foot fall is like adding an extra foot of fall on an already stretched rope.

Except a dynamic rope doesn't stop stretching...till it breaks.

That's my point.

In other words, the phobia about extension in the Sliding X (with limiter knots) producing "shock loading," or for that matter, ANY significant increase in loading, is looking almost certainly like another anchoring myth.

Hey all,

Dumb question coming up...What is the limiter knot in the sliding X that was mentioned?
The more I know the better.

Thanks

Does this hold up in the special situation where one is hauling loads off a sliding X setup with a static rope?

I'm not sure what you're asking, and my sense of it is that you already have an answer in your head--and you should simply state that answer and we can work from there.

To briefly answer the question of off angle loading on a cordelett, what happens (according to the testing) is that almost the entire load is taken by the shortest arm of the cordelette...

I'm just curious if you consider shock loading a "myth" in general. That, along with normal multi-pitch, you don't need to worry about the X shocking in a hauling accident or in a case of a heavy bag slipping off a ledge, or maybe a portaledge getting slammed up and down in a storm. I can't tell whether, from your description of the role of belaying in all this, you mean just climbing as opposed to also including the forces involved with all the other various big wall activities.

I'm asking because you're the one that's spent endless hours on all those wall anchors of varying quality over the years - I haven't but would still like to and am trying to figure out if it's worth it to do all the Chongo/PTPP major construction projects with cordalette powerpoints, etc. or should you just throw in a couple of X's and call it good...

John and Curt,

I guess I'm feeling incredibly stupid and dense on this because I'm not getting it at all. I think I've just been programming for way too many week/days/hours in a row now and am starting to lose it. Couldn't you guys show a little pity, put me out of my misery, and just answer this question for me because I really do want to know the answer?

So we have a bomber pro and a failing one equalized with a sliding X.

The good piece will take two yanks: the first one will be at the same force as the failure force of the poor piece. At this point, the fall is nearly consumed, and the rope still have (?) some stretching reserve.

The bad pro fails and the sliding X extends. Here occurs the second yank. Some of the energy of the fall is already dissipated by the rope stretch and the failure of the bad piece. The remaining energy will produce a load only on the good piece.

So, the total energy of the fall, which is a constant for a given fall, will be shared between the two yanks, instead of producing a single (shock ?)load on the system.

IMO, "how strong is the failing piece?" is an important aspect to think about. If it blows when you sneeze on it, the whole energy of the fall will load only the good anchor, which could produce it's failure as well. If the poor placement holds a fair amount of the force, it could work like a screamer by absorbing part of the energy of the fall before failing.

Could this be used as an emergency protection for a weak anchor or for belaying a leader on a little protection pitch ?
I mean that in extremis, one could intentionally place an additional weak piece of pro (say a 5 kN nut) which will lower the impact force on the system by braking if a shock occurs.
What do you think ?