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Homemade version of Metolius Equalizer sling
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Jun 7, 2016
I was looking at the metolius equalizer sling metoliusclimbing.com/equalizer... and was wondering if there is any reason why you couldn't just make one of these yourself out of 3/4 inch tubular webbing with a water knot tied on each end to make the loops. Is there anything blatantly wrong with a setup like this or am i missing something and everyone's gonna tell me i'm gonna die?




Rock Climbing Photo: Homemade Equalizer
Homemade Equalizer
Chris Gabrielli
Joined Jun 7, 2016
5 points
Jun 7, 2016
Rock Climbing Photo: kramer
Not pretending I know, just trying to use my brain and figure out.. would the water knots come loose over time as they are purported to do? Would you untie once in a while to check for any potential wear or damage? Hobo Greg
Joined Mar 30, 2016
64 points
Jun 7, 2016
You'd probably find a cordalette with a couple figure eights on the end does the same trick and is easier to manipulate, but sure what you have seems fine. jason.cre
Joined Aug 6, 2014
10 points
Jun 8, 2016
Rock Climbing Photo: Avatar
It will work. It will work well when you have 3 pieces exactly equidistant. It will work less well in all other cases.

Home made cordalette is much more flexible, and just as quick in almost any circumstances. Clip crabs from each piece of pro into the cordalette, pull all loops together to a central point, tie overhand or fig 8 to make powerpoint - done, and with the benefit of being roughly equalised for that specific belay. If the anchor pieces are further apart, you can untie the cord, put fig 8 loops in the ends, and do similar process.

As a confirmed crusty trad climber, I prefer to carry versatile pieces and engineer specific solutions on the spot, rather than carry lots of specialised gear. And yes, the rope itself is the most versatile solution :-)
Alex Rogers
From Sydney, Australia
Joined Sep 9, 2010
39 points
Jun 8, 2016
I love how you make comments like this:
J Marsella wrote:
Or, as about a thousand crusty trad climbers are about to say: just use the rope.

There is a reason why using the rope has pretty much been around for as long as the sport itself.

Where as you also mention passing fads like this:

J Marsella wrote:
Probably not gonna die but why reinvent the wheel. Look into the "Alpine Cock Ring" (ACR) equalizer for a more versatile one-trick pony.
patto
Joined Jul 9, 2012
25 points
Jun 8, 2016
Rock Climbing Photo: High Exposure
Chris Gabrielli wrote:
wondering if there is any reason why you couldn't just make one of these yourself out of 3/4 inch tubular webbing with a water knot tied on each end to make the loops. Is there anything blatantly wrong with a setup like this or am i missing something and everyone's gonna tell me i'm gonna die?


Nothing blatantly wrong as long as you understand the outside legs are single strand and the middle leg is double. Commercially, it's called a "rabbit runner" or "snake cord" and precedes the Metolious Equalizer by a long time.

Also, Bearbreeder and others have published similar things
mountainproject.com/v/10940238...

As far as the ACR that others have mentioned, there was a whole discussion here:
mountainproject.com/v/acr-anch...

and here:
rockclimbing.com/forum/Climbin...

/thread
wivanoff
Joined Mar 3, 2012
409 points
Jun 8, 2016
Rock Climbing Photo: My first belay certification.
I used to do this all the time with a standard 240 cm, 10 mm dyneema runner, rather than the homemade rabbit runner you're using. I clip the ends of the loop into the outer two carabiners (no knots on the end), and run the whole thing (both strands) through the center 'biner, pull and tie. You can do it with a 120 cm too, but your gear needs to be super close. You can also do it with 7mm cordalette in a loop, or tied like a rabbit runner.

But I've been learning to be more proficient using the rope, and I prefer that method.
Dylan B.
Joined Mar 31, 2006
971 points
Jun 8, 2016
Rock Climbing Photo: The traverse out to the Yellow Ridge on the Dogsti...
wivanoff wrote:
As far as the ACR that others have mentioned, there was a whole discussion here: mountainproject.com/v/acr-anch...


Executive summary:

(1) Tests by Jim Titt and the DAV make it clear that sliding systems (including the ACR) are no better than fixed systems at distributing loads in 3-piece anchors and are worse in terms of peak loads if a piece fails.

(2) No matter what you do with a 3-piece anchor, it is reasonable to expect that one of the pieces will get at least 50% of the load.

As for the homemade Equalizer version, it is fine. In addition to the references already given, it is the recommended big-wall anchor in Chris McNarmara's big-wall climbing book; see



but note that the main reason it is recommended is for four-piece big-wall anchors. For this purpose you need 20 feet of cordelette, and neither of the Metolius Equalizers is long enough.

Andy Kirkpatrick likes it too, see andy-kirkpatrick.com/articles/....

As mentioned, the double strand to the middle anchor could raise that anchor's load significantly (depending on the relative lengths of the anchor arms and their angles with the vertical).
rgold
From Poughkeepsie, NY
Joined Feb 15, 2008
544 points
Jun 8, 2016
FWIW, and I'm surprised this hasn't come up yet: the knot you're using on the ends would be an overhand on a bight, not a water knot. While effectively appearing the same in the end, a water knot is specific to tying two loose ends together.


Same cautions apply here as to tied slings, although I don't think an overhand on a bight is prone to the same creep issue a water knot is.




rgold wrote:
As mentioned, the double strand to the middle anchor could raise that anchor's load significantly (depending on the relative lengths of the anchor arms and their angles with the vertical).


Simply having two strands to the anchor point wont increase the load. You effectively have two parallel strands, so they share the same load a single strand would. Meaning: load at the anchor point is the same, but the load is shared between the two strands.

Unless I'm mis-understanding what you're saying here.
Brian L.
Joined Feb 19, 2016
81 points
Jun 8, 2016
Brian L. wrote:
FWIW, and I'm surprised this hasn't come up yet: the knot you're using on the ends would be an overhand on a bight, not a water knot. While effectively appearing the same in the end, a water knot is specific to tying two loose ends together. Same cautions apply here as to tied slings, although I don't think an overhand on a bight is prone to the same creep issue a water knot is. Simply having two strands to the anchor point wont increase the load. You effectively have two parallel strands, so they share the same load a single strand would. Meaning: load at the anchor point is the same, but the load is shared between the two strands. Unless I'm mis-understanding what you're saying here.


You are. The force on the piece is relative to the elasticity of the strands linking to that piece, all else being equal the piece linked by two strands experiences twice the force compared to a single strand. In practice none of it matters.
By the way the ACR is the most worthless belaying idea ever invented by someone with no idea about basic physics.
Jim Titt
From Germany
Joined Nov 10, 2009
365 points
Jun 8, 2016
hmm... Brian L.
Joined Feb 19, 2016
81 points
Jun 9, 2016
Jim Titt wrote:
By the way the ACR is the most worthless belaying idea ever invented by someone with no idea about basic physics.


Jim,
I was wondering if you had posted, or published your study on the ACR as linked in the thread rgold posted a few comments back (mountainproject.com/v/acr-anch.... I remember that thread, and the conclusions from it that i drew was that the ACR had some value, but was not a be all end all solution, providing some movement in the anchor, but not being good at displacing forces applied in the event of anchor failure.
Is there something else to this system I am missing? did you conclude something more dangerous about the system other than the potential for displaced forces in the event of blown gear or failure?
(I am bad at physics, forgive my ignorance)
thanks
goingUp
From over here
Joined Apr 9, 2013
68 points
Jun 10, 2016
Brian L. wrote:
Simply having two strands to the anchor point wont increase the load. You effectively have two parallel strands, so they share the same load a single strand would. Meaning: load at the anchor point is the same, but the load is shared between the two strands. Unless I'm mis-understanding what you're saying here.


Even if your strands were 100% static, your logic is wrong.

Ignore what the strands are attached to, and just look at the anchor point. If someone applies a 12 kN force downwards on the anchor, that will be distributed to the 4 strands going outwards. Best case, each gets a 1kN load (angles of pull will, of course, change this). So, if all 4 strands go to independent, but very close together attachment points (say, vertically above each other), then all the strands are parallel, and each applies 3 kN to its attachment point. Now, if we take two of the strands and attach them both to the same attachment point, the anchor end of the setup doesn't somehow "magically" know they are going to the same anchor point, so change this to 4 kN on each of three anchor points. All 4 strands still get 3 kN, and that double-strand anchor point gets 6 kN.

Where stretch comes in, is if the arms are unequal length, then the longer arms will apply less force to their anchor points than the shorter arms. Since the double-arm is generally the center arm in these setups, it is often shorter, so increasing the force on it. And because it is also often the most-aligned with the (downwards) force of the fall, it will also generally get more force due to the geometry.

Put it all together, and you'd expect well over 50% of the force on that piece/attachment point.
David Gibbs
From Ottawa, ON
Joined Aug 18, 2010
10 points
Jun 10, 2016
Rock Climbing Photo: BD Fuel
David Gibbs wrote:
Even if your strands were 100% static, your logic is wrong. Ignore what the strands are attached to, and just look at the anchor point. If someone applies a 12 kN force downwards on the anchor, that will be distributed to the 4 strands going outwards. Best case, each gets a 1kN load (angles of pull will, of course, change this). So, if all 4 strands go to independent, but very close together attachment points (say, vertically above each other), then all the strands are parallel, and each applies 3 kN to its attachment point. Now, if we take two of the strands and attach them both to the same attachment point, the anchor end of the setup doesn't somehow "magically" know they are going to the same anchor point, so change this to 4 kN on each of three anchor points. All 4 strands still get 3 kN, and that double-strand anchor point gets 6 kN. Where stretch comes in, is if the arms are unequal length, then the longer arms will apply less force to their anchor points than the shorter arms. Since the double-arm is generally the center arm in these setups, it is often shorter, so increasing the force on it. And because it is also often the most-aligned with the (downwards) force of the fall, it will also generally get more force due to the geometry. Put it all together, and you'd expect well over 50% of the force on that piece/attachment point.


In a 100% static anchor [Unobtanium] all 3 legs would get the same load.

With a sling/cord anchor with relatively equal length legs as seen in the original post. The middle double legs will stretch less than the single outer legs because it's splitting the load between two strands. Since it stretches less it will require more load to stretch the same amount as the outside legs.

Jim Titt wrote:
The force on the piece is relative to the elasticity of the strands linking to that piece, all else being equal the piece linked by two strands experiences twice the force compared to a single strand. In practice none of it matters.
rocknice2
From Montreal, Quebec
Joined Nov 27, 2006
3,024 points
Jun 10, 2016
David Gibbs wrote:
Best case, each gets a 1kN load (angles of pull will, of course, change this). So, if all 4 strands go to independent, but very close together attachment points (say, vertically above each other), then all the strands are parallel, and each applies 3 kN to its attachment point. Now, if we take two of the strands and attach them both to the same attachment point, the anchor end of the setup doesn't somehow "magically" know they are going to the same anchor point, so change this to 4 kN on each of three anchor points. All 4 strands still get 3 kN, and that double-strand anchor point gets 6 kN.


Edited. Your 1kn load thing confused me, and this is written really weirdly but I think I see what you're saying now. however, you're saying the exact same thing as I am. The difference is I'm talking about a system with 3 strands vs 4 strands going to three attachment points. It matters.

If the center point receives a 6kn load then in a 3 strand system the single strand supports 6kn. In the 4 strand system each strand supports 3 kn.

Think about it like this. If you have a 12kn load going to 1 anchor point, that anchor point support 12kn, regardless of how many strands are attached to it. The load each strand support is split the more strands there are.

If you disagree with this, then draw out a free body diagram for an anchor system like the OP showed and solve for the loading with 3 strands vs 4 strands. If you do it correctly you'll see what I'm saying.

rocknice2 wrote:
In a 100% static anchor [Unobtanium] all 3 legs would get the same load.


Actually, unless they were all parallel, they wouldn't. It depends on the geometry. The force in direction of the load would be equal, but any leg that was angled off that axis would have an additional force component normal to the load axis. So the force vector along the strand would be higher.




All this talk about the dynamic properties in an anchor made from nylon slings has me thinking. What is the effective spring rate of a nylon sling? How much of a factor is it really, vs an idealized static system? At what point will a sling permanently deform? Has anyone actually studied that?
Brian L.
Joined Feb 19, 2016
81 points
Jun 10, 2016
Brian L. wrote:
You really don't know what your talking about. This makes no sense. Draw out the free body diagram for the static cases and solve it. You'll see what I mean. Actually, unless they were all parallel, they wouldn't. It depends on the geometry. The force in direction of the load would be equal, but any leg that was angled off that axis would have an additional force component normal to the load axis. So the force vector along the strand would be higher. All this talk about the dynamic properties in an anchor made from nylon slings has me thinking. What is the effective spring rate of a nylon sling? How much of a factor is it really, vs an idealized static system? At what point will a sling permanently deform? Has anyone actually studied that?



OMG YOU ARE SO SMART!!!!!!!!!!!!!!!!!!!!!!!!
jason.cre
Joined Aug 6, 2014
10 points
Jun 10, 2016
Brian L. wrote:
Edited. Your 1kn load thing confused me, and this is written really weirdly but I think I see what you're saying now. however, you're saying the exact same thing as I am. The difference is I'm talking about a system with 3 strands vs 4 strands going to three attachment points. It matters. If the center point receives a 6kn load then in a 3 strand system the single strand supports 6kn. In the 4 strand system each strand supports 3 kn. Think about it like this. If you have a 12kn load going to 1 anchor point, that anchor point support 12kn, regardless of how many strands are attached to it. The load each strand support is split the more strands there are. If you disagree with this, then draw out a free body diagram for an anchor system like the OP showed and solve for the loading with 3 strands vs 4 strands. If you do it correctly you'll see what I'm saying. Actually, unless they were all parallel, they wouldn't. It depends on the geometry. The force in direction of the load would be equal, but any leg that was angled off that axis would have an additional force component normal to the load axis. So the force vector along the strand would be higher. All this talk about the dynamic properties in an anchor made from nylon slings has me thinking. What is the effective spring rate of a nylon sling? How much of a factor is it really, vs an idealized static system? At what point will a sling permanently deform? Has anyone actually studied that?


The 1 kN was an editing error -- I changed my numbers for ease of use, and didn't back fix all of them.

When you wrote:

"Simply having two strands to the anchor point wont increase the load."

I read that as saying:

If we compare a system with 3 strands to 3 anchor points with a system with 4 strands, 2 of which go to the same anchor point, that won't increase the load on the anchor point (as compared to either the 3-strand system, or the other anchor points in the 4-strand system).

That is, if you have 3 (unobtainium) parallel strands to 3 anchor points, each will get a load of 4 kN. If you add a 4th parallel strand to one of the anchor points, that won't change the loads on the anchor points, and they will all still get 4 kN.

My argument is that with 3 strands, each carries 4 kN to wherever they go. With 4 strands, each strand carries 3 kN to wherever they go. If two go to the same anchor point, that anchor point will be loaded at 6 kN, and the other two at 3 kN. So, adding a 2nd strand to an anchor will increase the load (on that anchor point).

I can upload a set of free-body diagrams if you like. (But what I was trying describe is the result of the free-body-diagram analysis.)
David Gibbs
From Ottawa, ON
Joined Aug 18, 2010
10 points
Jun 10, 2016
goingUp wrote:
Jim, I was wondering if you had posted, or published your study on the ACR as linked in the thread rgold posted a few comments back (mountainproject.com/v/acr-anch.... I remember that thread, and the conclusions from it that i drew was that the ACR had some value, but was not a be all end all solution, providing some movement in the anchor, but not being good at displacing forces applied in the event of anchor failure. Is there something else to this system I am missing? did you conclude something more dangerous about the system other than the potential for displaced forces in the event of blown gear or failure? (I am bad at physics, forgive my ignorance) thanks


Perhaps I was a bit harsh, after all the Trango Alpine Equaliser tested out even worse!
The ACR replaces a multi-purpose item (a karabiner) with a tied-in rap ring and ends up performing equally badly in the equalisation stakes (three piece anchor) or worse (two piece anchor) than a normal sliding X system with no benefits.
Jim Titt
From Germany
Joined Nov 10, 2009
365 points
Jun 10, 2016
David Gibbs wrote:
TMy argument is that with 3 strands, each carries 4 kN to wherever they go. With 4 strands, each strand carries 3 kN to wherever they go. If two go to the same anchor point, that anchor point will be loaded at 6 kN, and the other two at 3 kN. So, adding a 2nd strand to an anchor will increase the load (on that anchor point). I can upload a set of free-body diagrams if you like. (But what I was trying describe is the result of the free-body-diagram analysis.)


No, you're analyzing this incorrectly. The force on each anchor if the loading is truly parallel (impossible) is the load divided by the number of anchors.

THEN you can analyze the load on the stands. So the load on the doubled strand would be 2kn each.

This is much easier to see if you don't analyze an impossible case. I say this, because it took me a bit to figure out where you were going wrong. It sounds very logical, but it's not correct.

For instance, you can't apply the same reasoning if the strands aren't all parallel. You can't look at the master point and just "know" what load is going along each strand like you are implying here. They're unknowns until you do the sum of forces at each anchor.

Seriously, look at a case like the OP posted. Do the proof and you'll see. You can't figure out what the loads are at the "master point" until you figure out the loads at each anchor point.
Brian L.
Joined Feb 19, 2016
81 points
Jun 10, 2016
I'll have to do some reading. It could very well be that I'm wrong. David Gibbs
From Ottawa, ON
Joined Aug 18, 2010
10 points
Jun 10, 2016
Rock Climbing Photo: BD Fuel
Brian: I always assumed the legs of the anchor to be at zero degrees or pretty close to it. That's just for ease of calculation. Your right that once the legs start to widen it adds another component to the math. That's why it's easier to talk about an anchor with equal and parallel legs.

We know exactly how much force is at the master point, 12kn. It's the anchor points that require math.
rocknice2
From Montreal, Quebec
Joined Nov 27, 2006
3,024 points
Jun 10, 2016
In theory land (which is what we are discussing) a double strand in a self equalising system will carry twice the load of a single strand piece. Brian L. they are correct. Get equal strands to each piece though and you do get equal forces on them all. (in theory land)

For a non self equalising anchor theory also means that longer anchor arms carry less load. Half as much if they are twice as long. That said, geometry plays a role here too, a two arm system V system suggests equal loading if you predict the load direction correctly and there is minimal stretch. (3 arms is indeterminate on simple geometric analysis.)

But start throwing a few more realities in to the system and the goal to equalise forces proves itself to be nigh on impossible. Friction at the equalisation point screws up self equalising systems. For non equalising systems you can get things pretty close with 2 arms (with horizontally level pieces) but it is almost impossible with three.


In the real world if you succeed some load equalisation then you have done your job. Get back to climbing.



My knowledge of the real world behaviour comes a fair bit from testing done by others including Jim. But it also comes from being on the cliff. If you have a second loading your anchor, take the time to pluck the lines. You can get a reasonable guess on the load their taking.
patto
Joined Jul 9, 2012
25 points
Jun 10, 2016
For a better understanding of "single vs. multiple" strands in an anchor a good paper was presented at the International Technical Rescue Symposium - "Tying it all together - Considerations for equalizing multi-pitch anchor systems."

You can read the article at:
riggingforrescue.com

Click "Research" then "Recent Projects"
Marty C
Joined Aug 27, 2008
80 points
Jun 10, 2016
Marty C wrote:
For a better understanding of "single vs. multiple" strands in an anchor a good paper was presented at the International Technical Rescue Symposium - "Tying it all together - Considerations for equalizing multi-pitch anchor systems." You can read the article at: riggingforrescue.com Click "Research" then "Recent Projects"


Thanks.

Hard link for those who are lazy:
riggingforrescueassets.s3.amaz...
patto
Joined Jul 9, 2012
25 points
Jun 10, 2016
Rock Climbing Photo: The traverse out to the Yellow Ridge on the Dogsti...
I think the underlying problem with the debate about how the loads would distribute in some ideal system is that the answer cannot be a consequence of just the free-body diagram. You have to consider elongation in order to solve for the anchor loads; without the additional equations provided by the deformation descriptions, the two equilibrium equations (one for horizontal equilibrium, one for vertical equilibrium) have more unknowns (four, one for each strand) then there are equations and so are indeterminate in the sense that there are infinitely many solutions (linear agebra 101). Both of the solutions advanced by David and Brian are valid solutions to the equilibrium equations, you can settle on one or the other as well as infinitely many other choices, not from the equations, but only by imposing some predetermined view of how things ought to be. But that's theology, not physics.

In the case of fully rigid arms, i.e. the cordelette replaced by a truss, one can also enlist the fact that the net torque at any point has to be zero and so get more equations that way. But with cord (or cable or chains), no torque is available and deformations (possibly quite small for the metal examples) are still required to pin down a solution.

There is a big literature on this in the engineering world; the buzz words are statically indeterminate systems.
rgold
From Poughkeepsie, NY
Joined Feb 15, 2008
544 points
Jun 10, 2016
rocknice2 wrote:
In a 100% static anchor [Unobtanium] all 3 legs would get the same load.


If the material were purely static (think steel cable), if the legs were even 0.001% off balanced, one leg would get 100% of the load, the others 0. Easier to picture this with a two leg anchor - at anything other than the magic loading direction, one leg gets ALL the load. So static material is NOT the answer.
Gunkiemike
Joined Jul 29, 2009
2,678 points


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