Homemade version of Metolius Equalizer sling


Original Post
Chris Gabrielli · · Unknown Hometown · Joined Jun 2016 · Points: 5

I was looking at the metolius equalizer sling metoliusclimbing.com/equali... 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?

Homemade Equalizer

Hobo Greg · · Unknown Hometown · Joined Mar 2016 · Points: 110

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?

jason.cre · · Unknown Hometown · Joined Aug 2014 · Points: 10

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.

Alex Rogers · · Sydney, Australia · Joined Sep 2010 · Points: 40

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 :-)

patto · · Unknown Hometown · Joined Jul 2012 · Points: 25

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.
wivanoff · · Northeast, USA · Joined Mar 2012 · Points: 472
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
http://www.mountainproject.com/v/109402384

As far as the ACR that others have mentioned, there was a whole discussion here:
https://www.mountainproject.com/v/acr-anchor-method/106977191__1

and here:
http://www.rockclimbing.com/forum/Climbing_Information_C2/Gear_Heads_F40/Possible_ACR_variation_P2589752/

/thread
Dylan B. · · Unknown Hometown · Joined Mar 2006 · Points: 938

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.

rgold · · Poughkeepsie, NY · Joined Feb 2008 · Points: 525
wivanoff wrote: As far as the ACR that others have mentioned, there was a whole discussion here: mountainproject.com/v/acr-a...
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

https://www.youtube.com/watch?v=2q2PdnAAy6w

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/articl....

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).
Brian L. · · Unknown Hometown · Joined Feb 2016 · Points: 90

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.
Jim Titt · · Germany · Joined Nov 2009 · Points: 490
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.
Brian L. · · Unknown Hometown · Joined Feb 2016 · Points: 90

hmm...

goingUp · · over here · Joined Apr 2013 · Points: 40
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-a...). 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
David Gibbs · · Ottawa, ON · Joined Aug 2010 · Points: 6
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.
rocknice2 · · Montreal, Quebec · Joined Nov 2006 · Points: 3,018
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.
Brian L. · · Unknown Hometown · Joined Feb 2016 · Points: 90
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?
jason.cre · · Unknown Hometown · Joined Aug 2014 · Points: 10
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!!!!!!!!!!!!!!!!!!!!!!!!
David Gibbs · · Ottawa, ON · Joined Aug 2010 · Points: 6
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.)
Jim Titt · · Germany · Joined Nov 2009 · Points: 490
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-a...). 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.
Brian L. · · Unknown Hometown · Joined Feb 2016 · Points: 90
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.
David Gibbs · · Ottawa, ON · Joined Aug 2010 · Points: 6

I'll have to do some reading. It could very well be that I'm wrong.

rocknice2 · · Montreal, Quebec · Joined Nov 2006 · Points: 3,018

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.

Guideline #1: Don't be a jerk.

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