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VG62


Jan 19, 2010, 3:04 PM
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A Look at Load Distributing and Load Sharing Anchor Systems.
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Interesting comparative test of three-point anchors.
This report has been published in materials of ITRS-2007.
Links for download (pdf, 3.8 Mb):
1. http://rapidshare.com/...hor_Systems.pdf.html
or
2. http://depositfiles.com/files/2geg393vu
or
3. http://www.onlinedisk.ru/file/324515/


scottek67


Jan 19, 2010, 3:40 PM
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Rudmin


Jan 19, 2010, 3:48 PM
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VG62 wrote:
Interesting comparative test of three-point anchors.
This report has been published in materials of ITRS-2007.
Links for download (pdf, 3.8 Mb):
1. http://rapidshare.com/...hor_Systems.pdf.html
or
2. http://depositfiles.com/files/2geg393vu
or
3. http://www.onlinedisk.ru/file/324515/

I am guessing that this isn't what it appears to be. Haven't bothered to check the file.

EDIT: I stand corrected


(This post was edited by Rudmin on Jan 19, 2010, 3:53 PM)


Rudmin


Jan 19, 2010, 4:13 PM
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Interesting stuff. The way the anchor failure tests happened with the weight hanging and an anchor suddenly releasing seems a bit cut and dry. I wonder if there would be any difference in the anchor failure tests if you had a falling mass (climber) pull out the anchor via some sort of preplanned weak point so that you get the full dynamic effect of the momentum of the climber and the shock vibrations in the rope..


rightarmbad


Jan 19, 2010, 4:53 PM
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They stuffed up with the twin sliding X, of course the centre anchor is going to see twice the load, it's connected to both systems.
The ideal could never be what they postulated.


adatesman


Jan 19, 2010, 5:05 PM
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patto


Jan 20, 2010, 12:21 AM
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All the extension results from this testing are absolutely bogus for most climbing and rescue situations. They are getting 18kN+ loads because there is nothing dynamic in the system.

A mass should NEVER be directly attached to an anchor that can extend. Either ensure that there a dynamic attachment or that the anchor has absolutely minimal extension.


Thats I cannot fault the equalisation testing. Given the nature of this debate everybody will take their own personal slant on this study.

Personally after looking at the load sharing ability of the equalette vs the cordalette I fail to see a good reason why I should use an equalette. I've said it before K.I.S.S.


(This post was edited by patto on Jan 20, 2010, 12:22 AM)


scottek67


Jan 20, 2010, 1:17 AM
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adatesman wrote:
For anyone who'd rather not register to a suspicious file sharing service I've put a copy of the PDF here.
much appreciated Aric. U rock. Cool


(This post was edited by scottek67 on Jan 20, 2010, 5:05 AM)


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Mar 23, 2010, 9:50 AM
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This is excellent! I hadn't seen it before! Some of the results are predictable, but it's good to see real data!

The loads here seem reasonable for a rescue situation, but, unfortunately, not for most pure rock climbing situations.

Still, it does at least *hint* at the truth of what might happen in a hanging belay off an anchor when one arm blows. And if the loads were those you'd see in a worst-case scenario (which is exactly the one you build your anchor to handle) then you might expect to see loads like those in the study.

The main thing I wish is that they'd included some of the better anchors from the big anchors thread. Things like the CharlesJMM and the Mooselette make the equalette look like a poor first draft (IMO).

The best of the bunch in the thread were a beautiful blend of what the study calls load-sharing and load-distributing, with features of each. Unlike the load-sharing anchors in the study, these anchors had very little extension. The only real question is how well they'd equalize in a drop scenario - an answer that would have been well tested by this study.

GO


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rightarmbad wrote:
They stuffed up with the twin sliding X, of course the centre anchor is going to see twice the load, it's connected to both systems.
The ideal could never be what they postulated.

I'm not at all clear on why this should be. A simple diagram (ignoring for the moment the force multiplication through angles, and any friction/binding) suggests that the forces should look like this:



What are you seeing that I'm missing?

GO


bigjonnyc


Mar 23, 2010, 11:21 AM
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cracklover wrote:
rightarmbad wrote:
They stuffed up with the twin sliding X, of course the centre anchor is going to see twice the load, it's connected to both systems.
The ideal could never be what they postulated.

I'm not at all clear on why this should be. A simple diagram (ignoring for the moment the force multiplication through angles, and any friction/binding) suggests that the forces should look like this:

[image]http://i43.tinypic.com/qoc1o5.jpg[/image]

What are you seeing that I'm missing?

GO

Somehow your diagram is messed up. With a pull of X>0 on the bottom, this system will not remain static. Both the center and right anchors in your diagrams have uneven pulls from opposite sides of the webbing running through them. In a physical context this means acceleration, or one side of the anchor extending and the other contracting.


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bigjonnyc wrote:
cracklover wrote:
rightarmbad wrote:
They stuffed up with the twin sliding X, of course the centre anchor is going to see twice the load, it's connected to both systems.
The ideal could never be what they postulated.

I'm not at all clear on why this should be. A simple diagram (ignoring for the moment the force multiplication through angles, and any friction/binding) suggests that the forces should look like this:



What are you seeing that I'm missing?

GO

Somehow your diagram is messed up. With a pull of X>0 on the bottom, this system will not remain static. Both the center and right anchors in your diagrams have uneven pulls from opposite sides of the webbing running through them. In a physical context this means acceleration, or one side of the anchor extending and the other contracting.

That's not necessarily an problem - a standard cordelette will have differing tension in every arm. It simply means that there is uneven stress on the anchor points.

But upon further reflection, there *is* an issue with my diagram above: assuming no friction, the tension in every strand should be equal.

This is now what the forces look like they should be. So they look to me like (friction etc aside) they should be equal on each strand.



Edited to add pic ^^^

GO


(This post was edited by cracklover on Mar 23, 2010, 12:16 PM)


bigjonnyc


Mar 23, 2010, 12:05 PM
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cracklover wrote:
bigjonnyc wrote:
cracklover wrote:
rightarmbad wrote:
They stuffed up with the twin sliding X, of course the centre anchor is going to see twice the load, it's connected to both systems.
The ideal could never be what they postulated.

I'm not at all clear on why this should be. A simple diagram (ignoring for the moment the force multiplication through angles, and any friction/binding) suggests that the forces should look like this:

[image]http://i43.tinypic.com/qoc1o5.jpg[/image]

What are you seeing that I'm missing?

GO

Somehow your diagram is messed up. With a pull of X>0 on the bottom, this system will not remain static. Both the center and right anchors in your diagrams have uneven pulls from opposite sides of the webbing running through them. In a physical context this means acceleration, or one side of the anchor extending and the other contracting.

That's not necessarily an issue - a standard cordelette will have differing tension in every arm. It simply means that there is uneven stress on the anchor points.

But upon further reflection, there *is* an issue with my diagram above: assuming no friction, the tension in every strand should be equal. Will post another version shortly.

GO

That's what I meant by uneven pulls, differing tension on opposite sides of the cordolette running to an anchor


rightarmbad


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The way I read it was that they had a sliding x between anchor 1 and 2, a sliding x between anchor 2 and 3, then a sliding x to join the 2 original x's.
This would mean that anchor 2 was repesented in both x's and therefore would see twice the load and that would agree with their results.


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rightarmbad wrote:
The way I read it was that they had a sliding x between anchor 1 and 2, a sliding x between anchor 2 and 3, then a sliding x to join the 2 original x's.
This would mean that anchor 2 was repesented in both x's and therefore would see twice the load and that would agree with their results.

Are we talking about the same thing here? I see only one sling in this anchor:



GO


billl7


Mar 29, 2010, 11:14 AM
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cracklover wrote:



Edited to add pic ^^^

The problem here is that the pair of biners at the bottom are not evenly stranded. If you weight the power point it will pull down the right biner (less stranded) while the left biner (more stranded) goes up ... until the power point contacts the right biner at which point I guess it stabilizes (not quite enough coffee).

I'm assuming everything can slide and friction is negligible, which I think is the intent.

Bill L

Edit: I think I pretty much said the same thing as bigjohnnyc. And I'm assuming the power point is on a sliding X. Take that out and I think the stability issue goes away.


(This post was edited by billl7 on Mar 29, 2010, 11:23 AM)


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billl7 wrote:
I'm assuming the power point is on a sliding X. Take that out and I think the stability issue goes away.

It's not. See the picture I posted in the post above yours.

GO


ptlong


Mar 29, 2010, 3:08 PM
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GO, are you sure you can really see that poor photograph well enough to draw an accurate diagram? It sure isn't clear to me. While your sketch might be correct I think it's just as easy to see it as two sliding Xs with four strands going to the center anchor.

Now that would require you to believe that they screwed up their calculation of the ideal static loads. But look at the equalette case. They screwed up the ideal values for that one.


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ptlong wrote:
GO, are you sure you can really see that poor photograph well enough to draw an accurate diagram? It sure isn't clear to me. While your sketch might be correct I think it's just as easy to see it as two sliding Xs with four strands going to the center anchor.

You're right, it is a poor photo. But if you think you see four strands going to the middle of the three anchors, you need your eyes examined!

GO


ptlong


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I don't see 4 strands. But I don't see the one crossing from left to right down below either.

Here's another bad photo. It's not so bad that you won't be able to tell the configuration but I think it makes my point.




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ptlong wrote:
I don't see 4 strands. But I don't see the one crossing from left to right down below either.

Look at the strand of webbing on the right anchor that has the knot in it - running down to the left biner - and then up to the left anchor.

Do you not see that strand? Where else could it go?

GO


davidnn5


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Without wanting to sound too unscientific, what are the conclusions of the more gear-headed people here? I hate using webbing to start with as anchors and will generally use lengths of static rope with appropriate knots etc. I have money, and will pay for my life to be secure up to ~30kn. And wear a helmet. Yes, I'm that uncool.


(This post was edited by davidnn5 on Mar 30, 2010, 12:27 AM)


rightarmbad


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The original link I followed never showed any piccies.
I shall have another look.


ptlong


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GO, I see what you're talking about and it is suggestive. But I don't think this photo is good enough to really say one way or the other. It's just too easy to see things in a lousy photo, especially if you're already thinking it's supposed to be there.

Let's take another tack. If you're interpretation is correct the force on each anchor should be the same ideally. The angle between the left and right anchors looks like about 85 degrees or so. For the 595 lb load that would give a value of 240 lbs on each anchor.

If instead four strands go to the center, the ideal would be 171 lbs for the side anchors and 342 lbs for the center one.

The actual mean values they measured were: 195 lbs (left) 365 lbs (center) 189 lbs (right).

Now any monkey would quickly discover that this anchor binds like crazy. But is this the reason the results do not come close to matching the ideal case? Or is it rigged so that it wouldn't?

I don't know.


(This post was edited by ptlong on Mar 30, 2010, 7:56 PM)


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ptlong, I'm open to other interpretations of the pic, because, as you said, the detail in the pic is poor. But the photo is far from uninterpretable. Sure, it is difficult to tell where the strands are going as they get to the two power-point biners, so I'm open to other interpretations. But beyond that, you can easily see every strand, and there are not four strands going to the middle anchor.

If you want to make an argument about how either the binding or the large angle could result in the data shown in the article, or if you see the configuration of the sling more clearly than I, in a way that's more consistent with the test results, I'm all ears. But just to say that the data from the forces prove configuration "X" does not make "X" so, when the other data (the photo) clearly invalidates "X" as an answer.

I suppose you could also argue that the pic displayed with that set of data was not actually the anchor configuration tested. That would be a serious allegation against the authors of the article, but at least it would be consistent with the data.

GO


ptlong


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cracklover wrote:
I'm open to other interpretations of the pic...

...except for the only other interpretation so far offered (which you unequivocally rejected).


In reply to:
If you want to make an argument about...

I'm just saying that the photo is ambiguous. You're sure you can see all of the strands, but what if two of them are hidden as in the photo I posted? Then it comes down to interpreting small groups of noisy pixels down near the bottom carabiners. The written description doesn't help. The data, while interesting, do not resolve the question. And the fact that they did not correctly calculate the ideal values for all of the other anchors makes it harder to use that for support.

Who knows? And who would really care except that since the point of the paper is at best barely tangent to what recreational climbers are interested in it turns out that it's more fun to argue about a fuzzy photo.


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ptlong wrote:
cracklover wrote:
I'm open to other interpretations of the pic...

...except for the only other interpretation so far offered (which you unequivocally rejected).


In reply to:
If you want to make an argument about...

Sorry if it came across that way. But I wouldn't characterize your supposition as an "interpretation of the photo". You pretty much said that the photo is not interpretable. Is that not your position?

If I'm misunderstanding, then please explain where the two hidden strands are going after they come down from the middle anchor. Or are they consistently hidden entirely, throughout every curve and bend? Frankly, I don't even see what the configuration you're suggesting *is* that would allow two more strands to come off the top anchor. Perhaps you could explain that as a start.

GO


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cracklover wrote:
But I wouldn't characterize your supposition as an "interpretation of the photo". You pretty much said that the photo is not interpretable. Is that not your position?

I've been referring to two different interpretations so how is it that you would conclude that I believe the photo is uninterpretable? As I've said repeatedly, I think it is ambiguous.


In reply to:
Frankly, I don't even see what the configuration you're suggesting *is* that would allow two more strands to come off the top anchor. Perhaps you could explain that as a start.

So after all this you don't even know what the configurations we've been talking about are? That's funny. Okay, let's start with your configuration since you haven't described it in detail. Your diagram doesn't show how the strands travel through the carabiners. And the relative forces you indicated can't be right either, as you must have figured out by now. Let's see a more complete diagram from you.


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ptlong wrote:
cracklover wrote:
But I wouldn't characterize your supposition as an "interpretation of the photo". You pretty much said that the photo is not interpretable. Is that not your position?

I've been referring to two different interpretations so how is it that you would conclude that I believe the photo is uninterpretable? As I've said repeatedly, I think it is ambiguous.

Ambiguous is not an interpretation. Nor is saying there may be four strands to the middle anchor. An interpretation would be saying: "I see the loop of sling traveling through the anchor as such..."

I did not go into detail about how I thought the sling traveled because I thought it was clear from a combination of my diagram and then also my later description of the strand that connects the two sides. But if it's not clear to you, I'd be happy to give you a clearer schematic... tomorrow.

In reply to:
So after all this you don't even know what the configurations we've been talking about are? That's funny.

Huh? I have put forward an interpretation of one of their anchors. You have not.

In reply to:
Okay, let's start with your configuration since you haven't described it in detail. Your diagram doesn't show how the strands travel through the carabiners.

I thought that would be pretty obvious to anyone who took the time to really look at the photo, and look at my diagram. But as I said, I'd be happy to spell it out more clearly if you like.

In reply to:
And the relative forces you indicated can't be right either, as you must have figured out by now. Let's see a more complete diagram from you.

No, I have not figured out that the relative forces cannot be right. If you see a problem with the forces in my diagram, please point them out.

GO


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cracklover wrote:
Ambiguous is not an interpretation.
ambiguous - adj. - 1. Open to more than one interpretation; 2. Doubtful or uncertain.


In reply to:
I did not go into detail about how I thought the sling traveled because I thought it was clear from a combination of my diagram and then also my later description of the strand that connects the two sides. But if it's not clear to you, I'd be happy to give you a clearer schematic... tomorrow.

Yes, please draw a detailed diagram that shows how the strands travel through the carabiners. Also include the tensions in the strands and how these sum to support the load.


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ptlong wrote:
cracklover wrote:
Ambiguous is not an interpretation.
ambiguous - adj. - 1. Open to more than one interpretation; 2. Doubtful or uncertain.

Okay, so you've clearly got nothing to add to this conversation. You just think that somehow there are two mysterious invisible strands in the photo, and where they go or come from is irrelevant. Thanks, that's *super* helpful.

In reply to:
Yes, please draw a detailed diagram that shows how the strands travel through the carabiners. Also include the tensions in the strands and how these sum to support the load.

Here it is again, spelled out:


A -> B -> C -> D -> E -> F -> A

GO


ptlong


Apr 2, 2010, 5:15 PM
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cracklover wrote:
Okay, so you've clearly got nothing to add to this conversation.

Gabe, one thing at a time. You confused ambiguous with uninterpretable so I provided a dictionary definition to hopefully clear that up. Do you now understand the difference?


In reply to:
You just think that somehow there are two mysterious invisible strands in the photo, and where they go or come from is irrelevant.

They could be hidden in the photo. Look at the picture I posted for an example of this.


In reply to:
Here it is again, spelled out:

That is the same diagram and flawed force analysis. You just tacked on redundant labels. How do the strands wind through the carabiners?


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Apr 4, 2010, 8:51 PM
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ptlong wrote:
That is the same diagram and flawed force analysis. You just tacked on redundant labels. How do the strands wind through the carabiners?

You can't just state that it's flawed. That's not how an argument works. You have to suggest a theory that you claim supports the data better, and make an argument for it.

As far as I can tell, the strands wind through the carabiners exactly as I stated: A -> B -> C -> D -> E -> F -> A

GO


rightarmbad


Apr 4, 2010, 11:03 PM
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The results in the most simple interpretation simply reflect the tape binding where it crosses.
This creates two separate cells that share a common piece that therefore gets twice the load of the others.


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Apr 5, 2010, 8:07 AM
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rightarmbad wrote:
The results in the most simple interpretation simply reflect the tape binding where it crosses.

As the tape binds, it should get closer and closer to the situation in which the tape is fixed between biners, which would result in the first force diagram I posted:



In reply to:
This creates two separate cells that share a common piece that therefore gets twice the load of the others.

Not sure how you arrive at this. The load should be equally shared between the bottom two biners. Of the three upper biners, each gets two strands. Not sure why you would think the strands to the middle (upper) biner would somehow be transmitting more force than the strands to the outer two (upper) biners.

GO


ptlong


Apr 5, 2010, 2:02 PM
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cracklover wrote:
You can't just state that it's flawed.

You're choosing to ignore the angle which at around 90 degrees results in a fairly large error. Notice how their measurements for the anchors add up to quite a bit more than the load.


In reply to:
As far as I can tell, the strands wind through the carabiners exactly as I stated: A -> B -> C -> D -> E -> F -> A

What I meant was how they go through the carabiners and which strands are on top or bottom. It's possible to make more than one anchor that fits your schematic. When I look at a closeup of the photo I can't really be sure how the strands are going through the center. Although you've said you aren't sure either, can you label the photo? Where do these strands go with respect to the carabiners and one another?




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Apr 5, 2010, 2:06 PM
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cracklover wrote:
As the tape binds, it should get closer and closer to the situation in which the tape is fixed between biners, which would result in the first force diagram I posted

This isn't correct. If the angle were zero as you're treating it, the stretch, and hence the tension, in each strand would be identical.


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Apr 5, 2010, 2:12 PM
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ptlong wrote:
cracklover wrote:
You can't just state that it's flawed.

You're choosing to ignore the angle which at around 90 degrees results in a fairly large error.

No it doesn't. I'm not discussing the total force, but rather the distribution of force amongst the anchors. Which, ignoring friction, is unchanged by the angle between anchors.

In reply to:
In reply to:
As far as I can tell, the strands wind through the carabiners exactly as I stated: A -> B -> C -> D -> E -> F -> A

What I meant was how they go through the carabiners and which strands are on top or bottom. It's possible to make more than one anchor that fits your schematic. When I look at a closeup of the photo I can't really be sure how the strands are going through the center. Although you've said you aren't sure either, can you label the photo? Where do these strands go with respect to the carabiners and one another?


I have no idea. Ignoring friction, it makes no difference which strands are on top, and which aren't. If your argument is that my schematic is right (ignoring friction), come out and say so.

But I think that your argument is that you have no idea what's going on, and think that I shouldn't claim that I do.

Until you have a better theory to propose, I'm done discussing the matter with you.

GO


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Apr 5, 2010, 2:14 PM
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ptlong wrote:
cracklover wrote:
As the tape binds, it should get closer and closer to the situation in which the tape is fixed between biners, which would result in the first force diagram I posted

This isn't correct. If the angle were zero as you're treating it, the stretch, and hence the tension, in each strand would be identical.

Wrong. I don't think you understand the basic physics of the situation.

Cheers!

GO


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Apr 5, 2010, 3:14 PM
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cracklover wrote:
I have no idea... I think that your argument is that you have no idea...

To me it's ambiguous, to you it's certain. I was hoping you would explain how you are interpreting the photo since it is difficult to discern the features. I can see evidence for either interpretation but no slam dunk. What happens to those strands in the center is important for that reason. But from your perspective the other information makes what happens in the center irrelevant.

As I've said, I think it's one of two possibilities: the one you advocate and the one described (and illustrated) on the first page of this thread as two sliding Xs with four strands going to the center.


ptlong


Apr 5, 2010, 3:28 PM
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cracklover wrote:
ptlong wrote:
cracklover wrote:
As the tape binds, it should get closer and closer to the situation in which the tape is fixed between biners, which would result in the first force diagram I posted

This isn't correct. If the angle were zero as you're treating it, the stretch, and hence the tension, in each strand would be identical.

Wrong. I don't think you understand the basic physics of the situation.

Oh come on Gabe, I know you're better than that. With the strands bound like a tied cordelette it's a simple application of Hooke's Law: six equal-length strands all displaced by the same amount --> same tensions.


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Apr 5, 2010, 3:46 PM
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ptlong wrote:
As I've said, I think it's one of two possibilities: the one you advocate and the one described (and illustrated) on the first page of this thread as two sliding Xs with four strands going to the center.

Yes, I've described my supposition of what it could be. But while I've repeatedly asked you for your theory, you have given me nothing. What is the two sliding-X configuration you are claiming fits the photo? If such a theory has been described and illustrated, I haven't seen it.

And you're wrong, with fixed lengths, it's not the same as a cordelette. There's no point in explaining to you why, since it's already been illustrated, and you just don't seem to get it. But if anyone else is curious, I'd be happy to explain.

GO


ptlong


Apr 5, 2010, 4:20 PM
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cracklover wrote:
Yes, I've described my supposition of what it could be. But while I've repeatedly asked you for your theory, you have given me nothing. What is the two sliding-X configuration you are claiming fits the photo? If such a theory has been described and illustrated, I haven't seen it.

There's a photo of it on the first page in this thread. Here:



And since it wasn't as easy to decipher as I thought it would be for you, here's a diagram a-la-cracklover:



A->B->C->F->G->H->E->D->A


ptlong


Apr 5, 2010, 4:24 PM
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cracklover wrote:
And you're wrong, with fixed lengths, it's not the same as a cordelette.

Fixed lengths IS a cordelette.


In reply to:
There's no point in explaining to you why, since it's already been illustrated, and you just don't seem to get it. But if anyone else is curious, I'd be happy to explain.

Ha ha, okay Gabe. You can go now.


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Apr 5, 2010, 8:39 PM
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ptlong wrote:
cracklover wrote:
Yes, I've described my supposition of what it could be. But while I've repeatedly asked you for your theory, you have given me nothing. What is the two sliding-X configuration you are claiming fits the photo? If such a theory has been described and illustrated, I haven't seen it.

There's a photo of it on the first page in this thread. Here:

[image]http://i44.tinypic.com/wmckd4.jpg[/image]

And since it wasn't as easy to decipher as I thought it would be for you, here's a diagram a-la-cracklover:



A->B->C->F->G->H->E->D->A

If you thought the photo was representing that, why didn't you just say so?!

GO


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