Self Equalizing or Sliding X Anchor

[counterfeitfake]

I've found over-analyzing safety actually creates unsafe situations.

 

ding ding ding

[Freeman]

As a rescue dude I become more aware of the forces on anchors and all other parts of the system, and consider "loaded", "tensioned", and "shock loaded" systems entirely differently. We commonly build statically loaded raising and lowering systems with very high factors of safety, normally equalizing anchors to one focal point (aka master point). When we start getting into tensioned systems, I personally believe they should be engineered - I have seen highly tensioned pickoffs that have enough mechanical advantage to move a truck being used as an anchor.

 

In the climbing environment I think it is worthwhile understanding the forces on anchors and how different slinging configurations load the anchors both statically and dynamically. Each year I do a little "Physics of Phalling" class for our local SAR group talking about these things - with a little high school geometry you can easily understand what is happening with your anchors.

 

Good bolts in good rock normally don't fail, but as you all know, short runners or the "american death triangle" (which I've come across on a number of rap anchors) really does dramatically increasing the loading.

 

Many years ago I assisted in a rescue in the N Cascades and later the victim told me that he listened as each pin was placed. He said he knew there wasn't one good pin in the rock, yet we lowered and belayed two people (200kg) for 600 feet of overhanging rock.

[whirlwind]

"if neither would break, there's no need for equalization."

 

This is a flawed statement. If I only clip one bolt at the anchor, it has to hold the entire load. If I clip two bolts with a "Death X" the load will be distributed between the two, making them less likely to fail.

 

exactly what i was going to say the =lization lessens the likely hood of failure due to less strain on both bolts/pieces

[scrambled_legs]

I've always wanted to have someone show me hard data that shock loading with a dynamic rope is more dangerous than having a semi-equalized anchor.

 

Whenever you tie a knot in the anchor and don't have it perfectly centered for a fall, you automatically have more weight on one piece. On climbs where there's a traverse to the anchor after the last piece, you can't center it. In the case of a second approaching the belay, if he falls before he pulls the last piece, it'll be a sideways pull, after he pulls the piece than falls, a downward pull. You can't set up the anchor with a knot and have it equalized for both. Also, if the knot is centered for a straight downward pull for the second but the next pitch wanders left or right before a piece is placed, it won't be equalized for the leader.

 

So what's more likely to blow your anchor, have the initial fall caught with the majority of the weight on one piece and then if it blows, all of the weight on the next pieces with no slack in the cord/sling etc? Or is it better to have the weight distributed equally among all pieces on the initial fall with the possibility of another 6' fall on the remaining pieces if one does pop?

 

The first way, you're far more likely to pop a piece on the initial fall and the second, more likely to pop another piece if one fails on the initial fall.

 

One thing that hasn't been mentioned is the dynamic rope is a lot more static after it is stretched out from the initial catch. So that shock load might be only 6 feet on a dynamic rope but that rope won't stretch nearly as far as it did on the intial catch.

 

Just another reason it'd be interesting to read that book, its now on my list.

[shaoleung]

John Long's new edition of the Climbing anchors book really does put to rest a lot of these questions. He has some hard data in there too. Kinda geeky, but worth a cover-to-cover read. This season I have been using the equalette and will never use a cordulette set-up again. It takes care of many equalization/extension problems.

 

As for the original question about building anchors where the fall line changes drastically with removing your final piece, or leaving your anchor - I believe there is no silver bullet. You have to factor this in to your engineering of an anchor. You may have to building two belay anchors and break one down once your second arrives. Another less gear intensive solution would be to build a two-piece jesus nut both for the second and then for the lead, right off the anchor.

[catbirdseat]

One thing that hasn't been mentioned is the dynamic rope is a lot more static after it is stretched out from the initial catch. So that shock load might be only 6 feet on a dynamic rope but that rope won't stretch nearly as far as it did on the intial catch.

 

This is another misconception that has been propagated by word of mouth. It's something that seems reasonable on its face, but it's not based on science. The rope retains its dynamic character. If it did not the test results would have shown higher loading on the remaining pieces. Certainly, you will have lost some ability to absorb energy as the knot will have cinched tight, but it's not as bad as some people believe.

[catbirdseat]

Interested persons might want to take a look at this:

 

http://www.rockclimbing.com/cgi-bin/forum/gforum.cgi?post=1637886;sb=post_latest_reply;so=ASC;forum_view=forum_view_collapsed;guest=18133629

 

Particularly RGold's rather long post on the first page. He makes the point that Jim's tests at Sterling were done with quite a bit of rope out. He makes a hypothetical case in which one piece fails when there is little rope out. In this case the load could actually be larger on the remaining piece because the fall factor is larger.

[scrambled_legs]

Interesting, sounds like its definately not black and white after reading RGold's post about how the tests were conducted. I think you may have missed one of his main points, or what I thought he was saying.

 

He mentioned that the importance of the falling weight on the anchor after the intial piece blows isn't the biggest concern as the tests show the secondary load doesn't produce higher figures, but the weight of the belayer falling on that second piece is a huge addition to the second load put on the anchor.

 

Depending on how they're tied in, the belayer can add to the force of the climber significantly with anchor extention and they are tied into a static system, unless using the climbing rope. Although they are only falling a small distance, they are adding to the overall force and unlike the climber, their weight is transferred to the anchor all at once with no elasticity in the system. Interesting how he figures Sterlings shock loading results are misleading until they add a belay weight tied into the anchor.

 

Whatever the answers they definately haven't been answered conclusively by Long or Sterling or anyone as of yet. Hopefully this test will develop into more tests. I definately appreciate Sterling for taking his time to research this.