I believe John Long did do tests with the 3 legged cordalette. But there was so much wrong with John Long's 'research' that it is hard to know where to begin.

The two legged cordalette is trivially easy to equalise well as long as there a proper 'V' angle formed. A three legged cordalette is almost impossible to get perfect but in my experience I can get rough equalisation without too much difficulty.

First, I don't think John Long himself was involved in the Sterling tests to which I'm referring. Those tests were performed by Jim Ewing, R&D manager at Sterling Ropes. The statistics were completed by Dr. Lawrence Hamilton and Dr. Callie Rennison.

Second, according to the test summary, they did not perform tests for a 3-legged cordelette rig. Only the 2-legged.

Would you mind detailing the flaws in Ewing's tests? The details of the experiments are laid out in the book and determined that the load distribution across the two legs were dismal: almost 800 pounds difference between the legs in a Factor 1 fall.

This difference in force seems significant to me. Is there debate surrounding how they performed those experiments?

John Long was also incorrect in his conclusion that shock loading doesn't matter...

I don't believe that was his conclusion. His conclusion was that when one point of an anchor failed, the shock loading measured on the remaining leg(s) of the anchor were not as significant as one might anticipate.
Curt

I believe that this is the thread that cracklover is referring to.
http://www.supertopo.com/...1/Equalizing-anchors

You have to scroll a fair bit to get to the figures.

Do try and read up on the various anchor building, equalization vs extension threads (like that one) before making up your own mind about this and keep in mind that more recent threads (like yours) tend to have fewer contributors and less debate due to fatigue over the topic.

and the more critical issue of arm length...

This is an interesting point that I always found myself pondering while tying rope anchors. The problem, of course, is that a shorter arm has less absolute distance to stretch than a longer arm under the same load, and so under a falling situation the shortest arm will end up taking the brunt. A fairly simple workaround is to deliberately tie the powerpoint so that the shorter arms remain loose when the anchor is unloaded. It should be relatively straightforward to work out a rule-of-thumb: for every foot of extra length, tie that arm x inches short so that under a moderate load the arms stretch to (relatively reasonable) equalisation.

Like this:



It takes a bit more thought and playing around and will never be perfect, but I'd bet money that once perfected it would outperform the standard approach.

All of these rigs and theories focus on getting some form of equalization between three pieces. Why three pieces?

What if the equalizing cordalette only had two arms and if one uses three pieces, two of those pieces are rigged to produce only one arm? Sure, 50% of the force/weight is on one piece, but if it's bomber...

I've been paranoid enough in one or two situations over the years to rig an anchor with more than three pieces, but when tying the cordalette or using the rope I just used sling craft or a carabiner to combine pieces so that my cordalette/rope only had two or three arms.

Äs...

Yeah, but if you get it only slightly wrong (by as little as a half an inch) then the long arm of your three-piece anchor gets zero force.

Umlaut?

Yeah, but if you get it only slightly wrong (by as little as a half an inch) then the long arm of your three-piece anchor gets zero force.

I think a better approach to "fixing" the standard cordelette would be to tie a large (like an extra two or three wraps) central knot, and leaving it loose. This gives you both the benefit that it will equalize itself a little bit, and also absorb some force. Unfortunately for hanging belays, you'll probably tighten it a bit already in the direction you're hanging. And, of course, as Jim Titt suggested earlier in the thread, all those strands in the knot will tighten themselves different amounts, so the force the pieces feel will never be properly equalized no matter what.

But really, the big issue with all non-self-equalizing solutions is that if you're even just a little bit off in anticipating the direction of force, you can wind up with all of the force on one piece. Not good.

This can happen very easily. Maybe you have equalized it perfectly for you, the belayer, standing on a ledge. But the leader falling past you will not have her rope run in the same direction - the ledge is in the way. It will instead pull more in an outward direction. If there is any vertical component to the pieces, the bottom one will take all or most of the load first, and if it pops, then the middle one, and if that pops, then the top one.

The same thing can happen from a horizontal perspective - if the falling leader's rope goes off to the side relative to the direction of anticipated force.

Edited to add - it is certain that leaving the knot loose, with a lot of wraps, would help solve this issue. How much? Who knows.

GO

This is an interesting point that I always found myself pondering while tying rope anchors. The problem, of course, is that a shorter arm has less absolute distance to stretch than a longer arm under the same load, and so under a falling situation the shortest arm will end up taking the brunt. A fairly simple workaround is to deliberately tie the powerpoint so that the shorter arms remain loose when the anchor is unloaded. It should be relatively straightforward to work out a rule-of-thumb: for every foot of extra length, tie that arm x inches short so that under a moderate load the arms stretch to (relatively reasonable) equalisation.

Like this:



It takes a bit more thought and playing around and will never be perfect, but I'd bet money that once perfected it would outperform the standard approach.

Well I took the quick and easy approach and worked on a two-piece anchor (at least for now).
The setup was a fairly narrow angled anchor with 30° included angle, two lengths of 9mm rope with fig 8 on a bight at one end as one would tie-in and clove hitched into karabiners at the pieces. Basically how one would belay if you were on half-ropes.
One leg was 1m (1000mm) long and the other 50cm (500mm) so half the length and the knots pre-loaded to 10kg to tighten them about the same as by hand.

The central point was lightly loaded to 20kg and the tension equalised by adjusting the piece position. A load of 200kg was applied (from a fixed direction) and the difference in the tensions was 24% more on the shorter leg.
To re-equalise the loads the shorter leg piece needed to be moved down 4mm which indicates how accurately we will have to judge things.

Clearly the rope stretches and slips in the knots, the longer leg stetched 130mm (12%) and slipped 120mm, the shorter leg stretched 80mm (16%) and slipped 130mm.
So we could correct for this at the set-up stage:- If the higher loaded leg slips 10mm more due to the increased force then we can add this to the initial length. Then we could correct the stretch for the different load which is 60mm not 80mm so we need to add in 20mm to get things equal so adding a total of 30mm into the short leg.
This actually moved the load imbalance over to the wrong side (the long leg got a higher load) so clearly too much.
After a fair number of attempts I found needed to tie the short leg 18mm slacker than it would normally be if they were initially equalised or 3.6% of the length.
Having a poorly dressed fig 8 or even using one round stock karabiner and one I beam karabiner on the pieces made more difference to the load imbalance than I could manually correct, the I beam karabiner locking the clove hitche locked up much faster, the slip on a 12mm HMS being over 50mm at these loads.

For a typical belay judging the lengths exactly enough is going to be a hopeless task but probably for something like a very long line from an anchor well back maybe a something could be gained.

The Sterling tests that John Long's book on Climbing Anchors summarized showed that a 2-legged cordelette with unequal legs knotted on a bight experiences an average difference of 3.5 kN between the two legs. This shows that cordelettes are miserable at equalizing even when properly "pre-equalized".

What I'm wondering is ...

Frankly, it strikes me
as a too-rigid and somewhat clumsy structure. Especially in contrast
to one I've sketched as an implementation of an "ELET" --2-legged
anchor ("extension-limiting equalization triangle"). It seems to me
that using the common, handy materials of 7mm (twinned) cord
(or other) and a 24"/60cm HMPE (Dyneema, mostly, these days)
tape sling, one gets simplicity, looow friction (for the *equalization*),
and greater flexibility (thinking that UNtying this will be possible,
and so the materials can do other tasks as needed; and the particular
tying --length of legs-- can be set per need, not pre-set & fixed).

[image]http://s14.postimage.org/v1w7tdw1p/knots_ELET_of_cord_sling_M888_1.jpg[/image]

[image]http://s13.postimage.org/xtxcw22df/knots_ELET_of_cord_sling_M888_2.jpg[/image]

Full images (+/- 130kb ; 888pix long side):

http://s14.postimage.org/...ord_sling_M888_1.jpg

http://s13.postimage.org/...ord_sling_M888_2.jpg


These have yet to meet a test device, but seem sound IMO.

*kN*

Why not improve on the knotted cordelette (meaning "cord", of nylon) with something that DOES equalize

Well there´s always the Shunt trick.

Because dynamic equalisation and no extension are an impossibility. Extension can pose significant dangers whereas the lack of in general equalisation does not.

(I'd have to be absolutely desperate to be building an anchor where I thought I needed to equalise the pieces for me to be safe)

Interesting... Are you actually advocating this as a useful way of constructing an anchor/belay? Or more as a novelty?

Your system does nothing better than any of the other common ones, merely adding some more complication and using more gear. And it will equalise just as badly as any of them as well.
And as Patto says, you can´t have equalisation without potential extension which we prefer to avoid to put it mildly.

What I took from Sterling's testing was that extension was far over-rated (and, Patto, where's the testing that proves otherwise, body in system?).

Certainly worth noting that even with a simplistic system doing extension tests McKently ...

Thanks, URLink/citation for Mckently (among his many testings)?

*kN*

Dropping a weight on a rope and allowing extension is naturally a very selective scenario and in fact it represents a situation which I have never encountered in my entire climbing career which is someone using a direct belay for a lead climber off a trad anchor. It reflects neither the worst case nor the usual situation where the belayer is directly in the system.

Regrettably when the belayer is attatched to the belay and one piece fails under the impact of the falling leader (which is the most likely event) the belayer is accelerated downwards not by gravity but the force imposed by the leader through the belay device.
Traditionally one was "plucked from the stance" to one´s doom but nowadays we can see that the acceleration is probably around 4g looking at the typical forces we can generate through a belay plate. So simple FF1 thinking is incorrect when reviewing extension because really you would get a belayer taking a FF4 equivalent onto the sling plus of course the still regrettably falling leader so we need to add maybe 4 to 6 kN as well. The smart and fast reacting belayer will of course drop the leader and grab the belay to reduce the combined impact!

All in all a somewhat worrying prospect which leads me to think that potential extension has no place in a belay, especially if you involve low-stretch materials.

Those test results need to be retold over and over and over again. The conclusions from the Sterling have been a damaging disservice to the climbing community.

All this is grossly violating the K.I.S.S. principle.