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wootles
climber
Gamma Quadrant
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Jan 19, 2007 - 09:39am PT
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I don't know if this is in the book but thought I'd put it up here as reference. I'm working on digging out some data but as I've mentioned earlier the computer that it is contained in suffered some damage during Sterling's recent move. To tell the truth I'm not even sure where that computer is at the moment or at least which one of the 8 or so hard drives laying around that it's on.
Here is a summary that Chiloe wrote up about the analysis of the tests. This may be in the book. While not a full on technical paper it is the best I have right at this moment.
Larry Hamilton
October 4 2006
BRIEF SUMMARY
-----------------------------
Anchor setup | Median absolute
(similar rigs | difference in
combined) | force (kN)
--------------------+--------
cordelette equal | 0.88
X equal | 0.26
cordelette unequal | 3.33
X unequal | 1.00
equalette unequal | 0.41
-----------------------------
In connection with John Long’s new anchors book, Jim Ewing at Sterling Ropes ran a series of drop tests to see how well different setups could equalize the load on the anchors. He started with two basic anchor configurations: equal-length legs (think of two pitons in the same horizontal crack) and unequal-length legs (like two pitons in the same vertical crack).
Cordelettes did a relatively poor job of equalizing the unequal-legs setup. The median difference in force felt by long and short legs was over 3kN. Even in equal-legs setup, the median absolute difference was close to 1kN. A sliding-X, in contrast, reduced the unequal-legs difference to 1kN, and the equal-legs difference below 0.3kN.
Because even the 1kN difference between sliding-X legs is significant, Long, Ewing, and soon others turned their attention to alternatives that might work better than the sliding X. One of these, currently being called the “equalette,” reduced the median difference between unequal-length legs to about 0.4kN.
Most of the other proposed variations have not yet been drop tested. It is possible that due to unforeseen friction some of them, like the sliding X, will prove to equalize better in the living room than in falls.
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raymond phule
climber
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Jan 19, 2007 - 10:00am PT
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Thanks,
what was the total force?
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wootles
climber
Gamma Quadrant
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Jan 19, 2007 - 10:23am PT
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Ok. Here's a small hunk of data but it doesn't include the egualette stuff or the shock loading stuff. I'm done looking for the other stuff for today and won't be able to look again for a couple of weeks.
There's more and I'll post it if or when I find it.
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Chiloe
Trad climber
Lee, NH
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Jan 19, 2007 - 10:47am PT
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The sum of the forces felt by both arms in the main series of cordelette/sliding X/equalette tests ranged from about 4 to 11 kN.
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wootles
climber
Gamma Quadrant
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Jan 19, 2007 - 11:05am PT
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I should mention that in the early stages of the testing, where I believe the above numbers came from, I was using a fresh rope for each of those sets of 3 drops. In later tests I used the same rope sample continuously. So the increases in the forces you see above are due to the loss of elasticity (increase in modulus) of the rope sample. I found that using the same sample of rope not only saved time but delivered more consistent total peak force. After a rope has seen a half dozen or so FF1 drops the elasticity property changes very little if at all. I think I was doing the drops at 3 minute intervals. It also says in the book what mass I used but right now I can't remember if it was 80kg or 100kg.
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raymond phule
climber
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Jan 19, 2007 - 11:24am PT
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Thanks for the info
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Largo
Sport climber
Venice, Ca
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Jan 19, 2007 - 11:50am PT
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The testing we did was always intended to be shared far and wide beyond just being printed in the book. We did everything possible in having it be as scientific as we could, given the time and resources. The numbers were crunched by two nationally recognized statistics gurs who are also climbers, and Wottles is recognized throughout the industry as the most comprehensive tester in the US, with all the fancy UIAA towers and computers and gadgets as well as all the experience. He was recommended to me by Kolin P. at Black Diamond.
Ideally, this kind of testing is an on-going affair that should be carried out by the AAC. That's how it's done in virtually every other country on earth. All private efforts will be limited.
We got the ball rolling, but I can't keep it rolling by myself, nor can Wottles.
JL
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Chiloe
Trad climber
Lee, NH
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Jan 19, 2007 - 12:11pm PT
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and Wottles is recognized
The climber formerly known as Wootles
;-)
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dirtineye
Trad climber
the south
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Jan 19, 2007 - 12:25pm PT
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How much wottle
Would a Wootler wot
If a Wootler would wot wottles?
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GOclimb
Trad climber
Boston, MA
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Jan 19, 2007 - 03:28pm PT
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Regarding this anchor, which I'm calling the two crossed-x slings:
Tito said:
>> I’ve used it [ed. two sliding x's with limiter knots to form a
>> three piece anchor] on many occasion and with the quad as per
>> Largo’s book it seems like a perfectly reasonably anchor, am I
>> missing something?
> a majority of force goes to the shorter leg? because it
What do you mean by shorter leg? There is the same length of webbing on both sides. In general, with crossed-x situations, because the biners act as (approximate) pulleys, the force is the same on a long arm as on a short arm. Look at it this, way - if the force started to get higher on the short arm than it was on the long arm, the sling material would slip through the biner towards the short arm until those forces were equalized again. Does that make sense to you? It is, in fact, why you see relatively good equalization on what the testers called the "unequal" setups.
Tito goes on to say, in regards to the mooselette:
> from looking at that rigging, it doesn't seem like it can
> equalize well because of all the friction produced by so many
> strands of cord running across biners.
In practice, it seems to equalize better than most. So far as I can tell, this is because there is typically only one strand moving through the power point (the movement through the other biners is very small, and not binding). But as Wootles pointed out, seeing this with body-weight or two bodies-weight doesn't tell us much about what might happen from a hard fall. Only a test rig could do that.
{snipped the rest of Tito's analysis, which seemed to be based on a faulty premise}
> hooking up a portaledge
> to an anchor and being able to get a good night's sleep does
> not prove that an anchor is reliable for trad climbing. unless
> you have test results that show otherwise, one can only assume
> that anchor won't equalize very well. the more strands of cord
> running around biners, the harder it is for an anchor to
> equalize. the two sliding x's with limiter knots would appear
> to be superior.
I have no idea why you would assume that. Build one yourself, it's very easy. You can feel that the tension equalizes at least approximately on the strands, and you can feel that even under with body weight, the strands move freely - which is not always the case with the sliding-x, and you can see that there are rarely strands moving in opposite directions to each other, which always happens with the sliding-x.
GO
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Crag Q
Trad climber
Louisville, Colorado
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Jan 19, 2007 - 03:38pm PT
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GOClimb, What route is that in the mosselette picture? It sure looks like Eldo, but I can't match it up in my mind with any route.
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GOclimb
Trad climber
Boston, MA
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Jan 19, 2007 - 03:48pm PT
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Crag_q wrote: GOClimb, What route is that in the mosselette picture? It sure looks like Eldo, but I can't match it up in my mind with any route.
Bingo! Good eye! Yellow ridge, just before the short traverse under the roof around pitch, what, four, I think?
GO
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Ed Hartouni
Trad climber
Livermore, CA
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Jan 19, 2007 - 03:50pm PT
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Thanks wootles and John, great to have this data out in public. I know that it is difficult to find the time to write a formal paper up for a journal, perhaps we can have a productive set of thoughts generated in this shared environment of the Forum...
...I'm between meetings now, but I will post some calculational thoughts I have regarding the results later...
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wootles
climber
Gamma Quadrant
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Jan 19, 2007 - 04:24pm PT
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The climber formerly known as Wootles
;-)
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Largo
Sport climber
Venice, Ca
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Jan 19, 2007 - 04:29pm PT
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I've actually got to go to a meeting now but if someone can scan all the test stuff from the book and post it here, perhaps something more can be wrung from it. I'd don't have a scanner here at my home office.
JL
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GOclimb
Trad climber
Boston, MA
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Jan 19, 2007 - 04:48pm PT
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Jstan wrote: I must be missing something. We all realize no two anchors have the same strength and we count on our ability to estimate this strength. Why are we trying to equalize the load??
Because the person who built the cordelettes that would have tested like these ones in a hard fall...
... probably didn't realize that there was essentially no equalization going on - all of the force of the fall would hit one piece, and, if ripped out, then hit the other piece. Not good.
GO
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jstan
climber
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Jan 19, 2007 - 08:34pm PT
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GOCLIMB:
Do I have it correctly. Your answer is " we are trying to equalize because in this data we failed"?
Just trying to understand. That is OK but does not address my question.
My question was this. If I think I have one piece good for 3000# and another good for 1000# - I should not try to equalize. I should try to put say 2000# on the strong one and 500# on the weak one. If I try to put 1500# on both - one will rip. If I don't equalize the total force the anchor system (the sum of the two) can be substantially increased. If done correctly the total force can be 4000# instead of the 3000# one gets after ripping the poor anchor.
Before you are done this is going to need some mechanical network analysis using stress/strain data for the kinds of nylon used.
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Trusty Rusty
Social climber
Tahoe area
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Jan 19, 2007 - 09:47pm PT
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After jugging up to my picture perfect iron curtain of 69 equalized pins, Dorton calmly stated "minimum 3 & max 5 dude"
With a typ. 500 lb load, equalizing is a must and the "perfect figure eight" is appropriate for walls.
C/Jones. . .that "partner" was right when it comes to wall climbing. . .. but as far as free routes the "sliding W" is probably better.
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john hansen
climber
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Jan 19, 2007 - 10:12pm PT
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This thought just came to me after reading these posts.
It seems that most , if not all, of the systems use 'static' materials.
What if you had a cordellet with dynamic qualities? Like a bungee cord that would stretch to help distribute the wieght to three or more anchors, if not'exactly..' equal, at least with less shock loads.
I know the first question would be "How do you haul the bags or jumar from it ?" It would have to have just enough stretch to make it work. Help me out here....The difference between gold line and modern ropes is amazing. Im sure they have the technology.
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cintune
climber
Penn's Woods
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Jan 19, 2007 - 10:22pm PT
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"What if you had a cordellet with dynamic qualities?"
Yates makes an 8mm "dynamic prussik" cord that sounds like what you're suggesting. Having none of the expertise of the main contributors here, I have no idea how it would work in an anchor, but it's out there.
And there's always screamers.
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