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Self-equalizing vs. static anchor


Original Post
John mac · · Boulder, CO · Joined Oct 2008 · Points: 105

So I am weighing the pros and cons of a self equalizing anchor system (like the sliding X or ACR) vs. a static anchor (Coordilett equalized, then tied off.)

The self equalizing self equalizes but if one pice blows it will shock load the others.

In the static system if one piece blows it does not shockload the others but the equalization is far from perfect.

Thoughts?

T.L. Kushner · · Salt Lake City, UT · Joined May 2009 · Points: 5

anchors 101: SRENE
Solid
Redundant
Equalized
NO
EXTENSIONS

my $.02

edit: i guess it also matters on whether you're talking about trad protection or bolts. and whether you're going to just be top roping from the anchor or leading up another pitch above it.

kpbo · · Fort Collins, CO · Joined May 2008 · Points: 30

I'm curious why you say a 'static' system can't be equalized?

Dave Alie · · Golden, CO · Joined Feb 2010 · Points: 75

My opinion is as follows: like everything else in trad climbing, the answer is "it depends". Both are advantageous in certain scenarios so learn them both and figure out when you like using them. If you have two straight up and down pitches, tying off the anchor so it's equalized in one direction is fine, can be easier to deal with, and won't move if one piece fails. If the next pitch wanders, or heads off in a different direction than the last one finished in, a sliding x is probably your bet. If you are worried about "shocking" the anchor in case a piece fails, tie extension-limiting knots. What I mean is, if you have a 3 point anchor and one or all of the pieces is far away from the master point, then tie an overhand in the loop of rope that leads to those pieces. That way, if said piece blows, you only introduce a fraction of the slack into the anchor. of note in this situation is that you can only "slide" as far as your knots will allow, but take that into account when you're building the anchor and deciding where to tie the knots, and it will rarely be an issue. As long as you understand the limitations of both and how to apply them safely, then it really becomes a personal preference issue in many cases.

One last thought: it is worth buying and reading "rock climbing anchors" by Craig Luebben (or any of book published by the mountaineers, for that matter). It's a great book that presents a lot of information in a very accessible way.

have fun

Dave

Gif Zafred · · Pittsburgh, PA · Joined Nov 2010 · Points: 5

I couldn't have said it better than Dave. Including the book recommendation! I would only use a sliding X if the pitch wandered back and forth a lot. Otherwise, equalize and tie a knot.

Buff Johnson · · Unknown Hometown · Joined Dec 2005 · Points: 1,145

The solid rock & solid pro using good angles are the critical parts.

The rigging method is trying to match your intended direction of travel to load distribution off of multiple points. You're not getting perfect equalization in any case and you're not working for redundancy.

However with the dynamic rope, you won't see anything high enough nor will you get "shockloading". Ultimately, your rope will fail before a solid anchor will. If the anchor failed, the pro wasn't solid and/or had exaggerated angles.

Larry S · · Easton, PA · Joined May 2010 · Points: 841

You need to really chose based on what gear you have and what the circumstances are. Obviously you want the best gear possible. If all the pieces in your anchor are bomber and the direction of loading can be reasonably anticipated, I feel a cordolette is a good choice. If the loading may wander significantly, then something with some self equalizing properties can be handy. I haven't used the ACR, but it looks quick to setup as you don't have to try and get that main knot tied just right.

Regarding what happens if 1 piece blows out, there are a number of factors I can think of. With a static equalized anchor, so long as the loading is in the anticipated direction, I would think it would be hard to rip a piece fully out unless it's very shallow, as soon as it would begin pulling, the distance to the master point would change and that piece would start seeing less load. The opposite side of that argument is that subtle shifts in the loading will cause one piece to see more load, but not a huge amount. (figure 2) Now, picture 3 pieces equally spread and tied off with a cordolete at about 60 degrees total angle. The cordolete should be tied so that it is bisected by the angle of the load, meaning if the load is straight down, this hypothetical anchor has i piece straight inline and the other two at 30 degrees. (figure 1) The piece on the right pulls. Because the cordolete is static, now a significant percentage of the load is seen by only the center piece because the load can't shift to bisect the two remaining pieces. (figure 3). If each piece was marginal, the anchor could zipper in this case.

Now we have the same anchor with an ACR. In normal loading, the tension on each strand is equal. If That piece blows out again (I can't diagram what will happen here because it's all in motion.), the anchor extends and shifts to share the load between the two remaining pieces, but as it does friction around the ring will cause one piece or the other to temporarily see the majority of the load, the equalization isn't instantaneous. Assuming you're load is hitting the anchor thru the climbing rope, there should be some dynamic effects of the rope/tie in knots/belay which will keep the shock load down. Those dynamic effects spread the impact load over time which also allows the anchor to attempt to become equalized before the peak load occurs.

I usually use a cordolete or other static anchor. On a more marginal anchor where I can't beef it up by adding more gear, I would give a self equalizing anchor more consideration, but I would try to balance that out with limiting the extension as much as possible. One thing I don't really like with most of the self equalizing systems is you're reliant on one cord/sling. I always back that up. With a cordolete, you have multiple isolated loops of the same cord.

Figure 1

Figure 1 - Stress distribution in a cordolete with perfect static equalization. You should actually try and tie the outer legs a little tighter than the center to share the load better.
Figure 2
Cordolete with the loading shifted 5 degrees off center. The load on the right strand increases, to match that on the center. Left leg isn't seeing much at all.
Figure 3
Stress distribution in a cordolete when one leg blows out. The load on the center strand spikes as it can't share it well with the left piece.

DannyUncanny · · Vancouver · Joined Aug 2010 · Points: 100

With correctly tied limiter knots, extension is not much of a problem. To obtain a full 360 degree circle of use from two points, limiter knots should not be any further apart than the distance between the two points of protection, any extra serves no purpose. They should also be centred about the midpoint between the two points. With this method, the maximum extension you can ever get is the distance between the two points of protection (for a sideways pull), and the more probable extension is half that distance (for a downwards or upwards pull). So for a typical bolted anchor which might be two bolts spaced 2 feet apart. You shouldn't ever be looking at more than 1 ft of possible extension.

It also helps to tie the knots so that one strand of your x is slightly shorter than the other. This lets the midpoint slide more easily I find because the strands don't bunch up against each other.

Yarp · · Unknown Hometown · Joined Jan 2011 · Points: 0
jmac wrote:So I am weighing the pros and cons of a self equalizing anchor system (like the sliding X or ACR) vs. a static anchor (Coordilett equalized, then tied off.) The self equalizing self equalizes but if one pice blows it will shock load the others. In the static system if one piece blows it does not shockload the others but the equalization is far from perfect. Thoughts?
Thoughts? Here's mine...

This subject has been hashed, rehashed, sussed, tied and put out to pasture on every climbing website on the interwebz. Not to mention the myriad collection of books available that answers this question directly. Searching MP alone will give you so many results you'll need an assistant to sort through them all. If that doesn't satisfy your lust for anchor info then I might suggest finding a mentor who can teach you hands on.

Based on the terminology you use it would appear that you need to go back to the basics and try to forget some things that you have "learned".

I agree with Mark Nelson. Good pro in good rock with good angles. That's all you need to know. Shock loading is a myth that doesn't make sense once you actually do the research and look at the forces involved. Big bomber gear in good rock isn't gonna fail no matter how you lash them together. Placing three pieces and cloving them all together nice and tight is perfectly acceptable as long as they are solid placements in solid rock.

Attempts to equalize are good but in the end, six shitty placements all perfectly equalized and set for direction of pull are not as good as clove hitching your rope to a couple of big stoppers in bomber constrictions. Dicking around with complex anchor matrix's for hours on end at the belay is a great way to make it difficult to find a belayer as well.

Not to say that the information you've been given and the graphs aren't loaded with good data (because they are and I appreciate them being posted) but it's all a bunch of theoretical number crunching that means nothing if you've got good pro in good rock with good angles. If you don't know what this means then you should borrow/buy John Longs "Climbing Anchors" and read it 3 or 4 times. All will be clear.

And just use the rope unless you're leading every pitch. As somebody else on MP stated a while ago "It's the strongest, most abrasion resistant and dynamic piece of gear you have with you. Why wouldn't you use it?"
Dan Hall · · Unknown Hometown · Joined Jun 2010 · Points: 0

equalette rather than cordolette. The testing results near the end of Long's book shows significant advantages. The equalette also provides more lattitude in terms of equalizing falls where the load isn't perfectly aligned with the expected direction of fall (when setting the anchor).

Matthew Fienup · · Ventura, CA · Joined Feb 2006 · Points: 7,281

I second what Yarp said, except buy Luebben's book and read it 3 or 4 times.

Yarp · · Unknown Hometown · Joined Jan 2011 · Points: 0
Pesterfield's book was pretty good too. Many, many others out there. Reading them all would be the best advice if you don't have anyone to help you out as you learn.
mattm · · TX · Joined Jun 2006 · Points: 1,381

Buy both the Gaines/Long 2nd ed Anchors AND Leubben's Anchors books.

They both cover things the other one does not or only touches upon. Gaines/Long has test results via Sterling on anchor loading and "shock" loading.

I like Leubben for the clarity of images and more up to date equipment. Gaines/Long covers REAL anchor "philosophy" better.

SERNE is kind of a "myth" in many ways. Both are worth the read.

Moof · · Portland, OR · Joined Dec 2007 · Points: 25

SRENE is an oxymoron.

You can never have full equalization without facing some extension. Period.

A better goal is SRELE.
Simple
Redundant (massively misunderstood by the community)
Equalized
LITTLE Extension

Sliding-X: Equalized, simple. NOT redundant (single cut failure mode on the sling) unless you tie limiter knots, or clove hitches at the pieces. NOT low extension unless you have a short sling or tie limiter knots (which limit the range of equalization). I still would knot kill my partner if her used a single good sling on a double bolt anchor, but I personally double them up the slings on the rare occasions I have used them.

Cordalette: Lots of discussion on these is already overkill. Very limited equalization, little to no extension, good redundancy (you can cut any 2 cords or pull 2 pieces of gear before failure). With good gear and mostly straight up and down routes it is still a very good solution for many anchor situations.

Equallete: Hybrid sliding X that trades a little extension for a region of equalization. Each half is statically equalized with a sliding-X in the middle equalizing those dynamically. The region of equalization is limited, especially on big-walls where you may need the anchor to hold horizontal loads as your partner cleans the last pitch, yet still be bomber for vertical loads once you start the next pitch.

ACR/Trango Equalizer: Equalization, but NO redundancy to cutting of the sling/cord. Extension is possible unless you use limiter knots.

ACR/Trango Equalizer with Clove Hitches on each piece: Slight reduction is equalization (50% max load vs. 33% without clove hitches), but you immediately get Low extension, and double redundancy (handles 2 cuts and/or 2 pieces blowing, though the extension can be large if two pieces blow).

Rope cloved in: Can be statically equalizied (i.e. 0-100% load on each piece depending on millimeters of error on the knot locations). Zero redundancy for cut rope (we accept this at all times when climbing with single ropes), but as much redundancy as you have extra pieces in. Works well with vertical cracks, poorly for horizontal (greatly effects extension and equalization).

Summary: Learn lots of methods, especially the underlying strengths/weaknesses. Approach each anchor with a keen eye towards would could go wrong and be prepared to modify your usual approach to assure that every anchor you make will keep you and your partner off the deck.

Rick Blair · · Denver · Joined Oct 2007 · Points: 266
Moof wrote: Rope cloved in: Can be statically equalizied (i.e. 0-100% load on each piece depending on millimeters of error on the knot locations). Zero redundancy for cut rope (we accept this at all times when climbing with single ropes), but as much redundancy as you have extra pieces in. Works well with vertical cracks, poorly for horizontal (greatly effects extension and equalization).
For this I would add the equalizing figure 8 with the rope.

For the equalette, the master point direction can be changed by adjusting the cloves.
DannyUncanny · · Vancouver · Joined Aug 2010 · Points: 100

Also the clove hitch master point is a good one. Clove yourself to a piece, clove the rope to another piece, clove your master point in between the two pieces. You can slide the knots around to whatever length you need, but it is still redundant. You can add more cloves, but you can only equalize two of them unless you make things more complicated.

wlashgraham · · Unknown Hometown · Joined Oct 2010 · Points: 0

I don't know how true this is, but i have heard the the sliding x does not equalize well if it is already weighted (e.g. a leader falls, loads, then pulls a piece on the fall, so the direction changes).any thoughts on this? I personally use webbing with full strength lops on either end. It is easy to equalize, static and I am more comfortable building my anchors with webbing then rope. (mtntools.com/cat/mt/webolet… kinda gimmicky but so easy...)

Pascal Ripoche · · Berkeley CA · Joined Oct 2010 · Points: 180
Evan Deis wrote:Larry your Finite Element Analysis is garbage. A cordolete cannot support a moment as your model can. This doesn't even make for a moderately good approximation.
That's a really helpful comment Evan.

@Larry: However, you should consider some elasticity in your rigging. If you use the traditional 7mm perlon cord which has significant elasticity, the load will be much more distributed.
Pascal Ripoche · · Berkeley CA · Joined Oct 2010 · Points: 180
wlashgraham wrote:I don't know how true this is, but i have heard the the sliding x does not equalize well if it is already weighted (e.g. a leader falls, loads, then pulls a piece on the fall, so the direction changes).any thoughts on this? I personally use webbing with full strength lops on either end. It is easy to equalize, static and I am more comfortable building my anchors with webbing then rope. (mtntools.com/cat/mt/webolet… kinda gimmicky but so easy...)
I actually read the same thing about the sliding X but cant remember where. However, about the webolette, I see one minor difference between webollet and cordalette : slings are (mostly) not elastic while a cordalette made of nylon cord is pretty elastic which can distribute the load over several protection.
DannyUncanny · · Vancouver · Joined Aug 2010 · Points: 100
wlashgraham wrote:I don't know how true this is, but i have heard the the sliding x does not equalize well if it is already weighted (e.g. a leader falls, loads, then pulls a piece on the fall, so the direction changes).any thoughts on this? I personally use webbing with full strength lops on either end. It is easy to equalize, static and I am more comfortable building my anchors with webbing then rope. (mtntools.com/cat/mt/webolet… kinda gimmicky but so easy...)
Which is why you should tie one strand a bit shorter than the other.

Anyways, the worse a system equalizes, the better it resists unexpected extensions. Think of it like the differential on a car. You can have a regular differential which distributes half of the power (load) to each wheel all the time, but if one wheel slips (protection fails) so that it can't apply that power, then you get a spin out where neither wheel is applying power, or in the climbing analogy, a free fall where both pieces become unweighted until you hit the full extension of the system. By contrast, a limited slip differential would be like a load sharing system that binds up and if one piece fails, then the other pieces don't immediately lose all of their load.

Also, a regular cordalette would be the equivalent of no differential, just driving both wheels at the same speed off of one axle. This means that the wheels can't spin out, but you might put all of the load on one side
Ben Walburn · · Unknown Hometown · Joined Jul 2007 · Points: 680

Has anyone here ever blown a piece from their anchor or had any problems with either anchor scenario failing in any way that wasn't due to their own mistake?

Guideline #1: Don't be a jerk.

General Climbing
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