Dyneema sling as anchor?

Kyle Tarry wrote:

I am not aware of any DMM videos that test large fall factors, when the load is connected to the anchor with a dynamic element such as the rope.  A system constructed as such will behave significantly differently than dropping a load directly onto the anchor without the dynamic element, and the resultant forces will be very different.  You cannot extrapolate the results of a non-dynamic test system to a dynamic one.

If there is a DMM video showing data to back up your claim, instead of being snarky, why not just copy and paste the link?

Kyle how many times do I have to link the DMM drop test vid for you? In that vid they eventually use rope to construct the anchor to compare it to slings and forces are reduced approx by half.

And you most certainly can assume that that documented reduction applies in other cases in proportion to the amount of rope. More for short falls onto the anchor less for long.

Some might like to believe that getting forces below 6kn to be neglible but I suggest they get more experience building an anchor out of small gear IRL when it matters and then tell me it is insignificant.

The issue is about load transmission to both anchors and bodies.  When absorbing the energy of a falling weight, dyneema is going develop much higher tension than nylon, in some cases enough to break the dyneema, although the test situations do not account for various other absorbing modalities that would in real situations keep the load below the breaking load.

When used as a tether, dyneema is going to produce much higher tensions than nylon for any given fall factor.  Although the prospect of breaking the tether is remote, the possibility of breaking either the anchor or injuring the body is less remote.  I've never heard of a dyneema tether breaking during a fall in the field, but there was an accident in the alps a few years ago when a tethered fall broke some in-situ rigging and the climber died.  How weak that rigging was, and whether a nylon tether would have produced a different outcome is a matter of pure speculation.  People say you shouldn't be falling on tethers anyway, but I find that to be a curious form of double-think in many situations, since if you really weren't going to fall you wouldn't need a tether.

When it comes to belay anchors, the question is what's going to be absorbing fall energy.  In general, the answer is the climbing rope, in which case the anchor rigging material is of negligible significance. Although nylon stretches more and so reduces rigging angles under load as well as providing better load distribution, it doesn't seem likely that one would, over the course of many trials, find much difference in peak anchor loads between dyneema and nylon rigging.  (The same holds for quickdraws and sllngs---the rope is doing the energy absorbtion, not the sling.)

The situation is more nuanced when it comes to how the belayer is connected to the anchor, especially in a semi or fully hanging belay, which is the subject of the warning in the OP's post.  In this case, there is some  potential danger if there is any slack in the tether and a factor 2 fall happens.  In that case, the belayer is pulled off the stance and you now have two climbers plus the load from the tensioned climbing rope falling an extra few inches on a tether that is pretty short to begin with, so maybe a factor 0.25 fall but with a whole lotta weight now having to be absorbed by the high-modulus tether.  I don't think anyone has tested the potential loads here, but there is every reason to expect some very high ones, beyond the UIAA  maximums for climbing ropes, and this explains the warning graphic in the OP's post.

When all the blabbing is over, what remains is a principle of outstanding simplicity;  connect the belayer to the belay anchor with the rope.  Don't use nylon runners, don't use dyneema slings, use the rope.

I maintain, Rich, that when the possibility of a fall onto the anchor exists building the anchor entirely out of the rope is valuable.

I don't disagree HB, an all-rope anchor is certainly the gold standard in reliability, robustness, shock absorbtion, and load distribution, and is much more adaptable to different configurations than anything else.  It is a bit of a drawback when leads aren't being swapped and when the anchor is substantially removed from the actual belay stance, but most of the time it is the best option.

That said, it is virtually never the primary shock-absorbing component of the belay system, so replacing it with dyneema rigging doesn't seem to me to be a big deal.  What is a potential problem, and was the subject of the OP's question, is whether it is wise to connect the belayer to the anchor with static material.

Dyneema and Nylon are great anchors material. Use them for cleaning and/or rappeling. Don't ever fall on them. Use a clove hitch in a multi-pitch scenario. Better yet, get some instruction and guidance regarding technical rock climbing so you know why you do the things you do and why you shouldn't do other things. Don't rely on the mountain project forums for safety.

Harumpfster Boondoggle wrote:

Kyle how many times do I have to link the DMM drop test vid for you? In that vid they eventually use rope to construct the anchor to compare it to slings and forces are reduced approx by half.

They're comparing the force on anchors, with the load connected directly to the anchor in a non-dynamic manner.  In other words, there is no rope connecting the load to the dyneema or nylon anchor.  If there was a rope connecting the load to the dyneema or nylon anchor, the initial loads would have been much lower, and the difference between the different anchor constructions would be much smaller.

And you most certainly can assume that that documented reduction applies in other cases in proportion to the amount of rope. More for short falls onto the anchor less for long.

No.  Not only is this not true, but we have very good data right here in this thread to prove it.

• In the DMM test, the difference between dyneema and nylon was on the order of 40%, when the sling didn't break (17 vs. 12 kN for 60 cm FF1, 19 vs 14 kN for 60cm FF2).
• In Zephyr's test in this very thread, the difference between them was 0.3 kN, in a FF1 scenario, with 1 m of rope in the system.

This test is a great showcase of how difference can be very large when you are only testing the anchor material alone, but become very small when you put a dynamic rope into the system.

Futhermore, Rich has made multiple statements that are in agreement with my argument:

When it comes to belay anchors, the question is what's going to be absorbing fall energy.  In general, the answer is the climbing rope, in which case the anchor rigging material is of negligible significance. Although nylon stretches more and so reduces rigging angles under load as well as providing better load distribution, it doesn't seem likely that one would, over the course of many trials, find much difference in peak anchor loads between dyneema and nylon rigging.

 That said, it is virtually never the primary shock-absorbing component of the belay system, so replacing it with dyneema rigging doesn't seem to me to be a big deal. 

Note that all of this applies to scenarios where the climber takes a high factor fall onto the anchor with the climbing rope, as that was the subject you originally replied to when claiming a 50% force reduction.  Scenarios where a tether is used to connect directly to the anchor, with no dynamic material in the mix, are different, and in that case use of more dynamic materials could be beneficial, depending on the circumstances.

Harumpfster Boondoggle wrote: you just don't get it.

Considering the test data in this thread, agreement from Rich and others, and the basic laws of physics, are you sure I'm the one who "doesn't get it"?

you don't see the fundamental problem and I can't help you, Kyle. There is a profound blind spot that you are struggling with, a rigidity of thought that I will never be able to fix.

Case in point: You think Zephyr's test somehow resolves the nylon versus dyneema debate for anchor construction but in reality it neglects the real issue which is that the anchor itself would be better built from the rope entirely to begin with.

That is where you would see the difference between Kidney damaging forces (6kn) and merely uncomfortable ones (3kn) in a drop test with the extra rope mitigating.

If people are going to go off on gear and drop test #woofuckery then the goal should be to use the gold standard (the rope) for their climbing instead of looking for ways to justify their purchase of pretty dyneema slings.

There are some instances where you can't or probably won't use the rope to build an anchor.

On multipitches where you are leading everything. You could of course untie on every stance and retie into the other end, and maybe you do that. I learned to use a nylon or dynema schling in this instance.

Or on multipitch rappels, you either use the existing tad, the steel chains, or you sacrifice some of your own schings. All static stuff.

Harumpfster Boondoggle wrote: That is where you would see the difference between Kidney damaging forces (6kn) and merely uncomfortable ones (3kn) in a drop test with the extra rope mitigating.

Building the anchor with the rope will not change the impact force from 6 kN to 3 kN (in the scenario we are discussing, when there is a high factor fall of the leader with rope in the system).  There is zero test data to support this assertion, a basic understanding of physics would show you that this isn't the case, and there has been agreement from multiple people in this thread that the anchor isn't the primary energy absorbing part of the system.  If you draw a simple free body diagram of the system and do the math on deceleration distance and force, you'll find this to be the case.  

In light of your continued dogged assertion that your claim is true, even in light of significant empirical and theoretical data that says otherwise, I don't see any reason to continue this discussion.

(By the way, you seem to think that I'm arguing against rope anchors.  I'm not.  I like rope anchors and use them all the time.  All I'm saying is that you don't get anything remotely approaching a 50% force reduction with them.)

Kyle Tarry wrote:

Building the anchor with the rope will not change the impact force from 6 kN to 3 kN (in the scenario we are discussing, when there is a high factor fall of the leader with rope in the system).  There is zero test data to support this assertion, a basic understanding of physics would show you that this isn't the case, and there has been agreement from multiple people in this thread that the anchor isn't the primary energy absorbing part of the system.  If you draw a simple free body diagram of the system and do the math on deceleration distance and force, you'll find this to be the case.  

In light of your continued dogged assertion that your claim is true, even in light of significant empirical and theoretical data that says otherwise, I don't see any reason to continue this discussion.

(By the way, you seem to think that I'm arguing against rope anchors.  I'm not.  I like rope anchors and use them all the time.  All I'm saying is that you don't get anything remotely approaching a 50% force reduction with them.)

You don't get it Kyle.

Do this test:

1. Clip Dyneema sling to bolts and form master point. Clip in weight to be dropped on a two foot leash of dynamic rope. Raise weight 2 feet(FF1) and drop. Record result.

2. Take 6' of dynamic rope and clip into bolts forming a master point between them with legs of about 2 feet each. Clip in rope and weight as before. Raise 2 feet and drop. Record result.

You now have effectively decreased the FF1 fall to a FF0.33 due to the extra dynamic rope in the system.

This is why building the anchor out of the climbing rope is especially good when there is any chance of a fall right above the belay onto the anchor.

Clove in with the rope to the anchor as you climb and use a nylon sling as a tether / rap extension when you descend.  What are the flaws with this method?  Does someone have a link to fall test data on nylon vs dyneema?

Harumpfster Boondoggle wrote:

You don't get it Kyle.

Do this test:

1. Clip Dyneema sling to bolts and form master point. Clip in weight to be dropped on a two foot leash of dynamic rope. Raise weight 2 feet(FF1) and drop. Record result.

2. Take 6' of dynamic rope and clip into bolts forming a master point between them with legs of about 2 feet each. Clip in rope and weight as before. Raise 2 feet and drop. Record result.

You now have effectively decreased the FF1 fall to a FF0.33 due to the extra dynamic rope in the system.

You calculated the fall factor wrong.  A 2-foot fall with a 2-foot single rope connection plus a 2-foot, 2-arm rope anchor isn't FF0.33.  It's approximately FF0.67, depending on the angle between the legs of the anchor, and some other nuances.  A 2-leg anchor is effectively twice as stiff as a normal climbing rope (because springs in parallel), and thus the 2 feet of extra rope in the anchor is effectively the same as 1 foot of additional single climbing rope.  2/3 = 0.67.  In this unlikely scenario where you take a fall before you're even out of reach of the anchor, the reduction in force might be ~30%.

And, this is for a fairly unlikely scenario of a fall of only 2 feet, with 2 feet of rope out.  In a more realistic scenario of the leader falling onto the anchor, such as they have traversed 5, 10, or 15 feet out, the difference is even smaller.  For example, if you're 10 feet out, the FF goes from 1.0 to 0.91.  If you're 20 feet out, the rope anchor only reduces the FF to 0.95.  In these cases, the force reduction is going to be on the order of 5-10%.

(Since you don't seem to understand basic rules of springs in series and parallel, you might reconsider accusing others of "not getting it."  If you care to learn more, this wikipedia article is quite helpful: https://en.wikipedia.org/wiki/Series_and_parallel_springs)

From this, we can make 2 conclusions:

• A rope anchor resulting in a full 50% reduction in impact force is unlikely in any real world scenario
• The actual reduction in force is dependent on a large number of factors, and as such making an authoritative numerical claim about the effect of a rope anchor, without talking about a very specific scenario, is quite ignorant.

You forgot the knots. Then we get close to the DMM number.

You also forgot that is the exact situation in the OP diagram.

But I'm glad you think I am an authority.

Harumpfster Boondoggle wrote:

You don't get it Kyle.

Do this test:

1. Clip Dyneema sling to bolts and form master point. Clip in weight to be dropped on a two foot leash of dynamic rope. Raise weight 2 feet(FF1) and drop. Record result.

2. Take 6' of dynamic rope and clip into bolts forming a master point between them with legs of about 2 feet each. Clip in rope and weight as before. Raise 2 feet and drop. Record result.

You now have effectively decreased the FF1 fall to a FF0.33 due to the extra dynamic rope in the system.

This is why building the anchor out of the climbing rope is especially good when there is any chance of a fall right above the belay onto the anchor.

I don't understand how this would work. If you have (2) 2' legs, you don't have 6' of rope in the system, you have 4'. Also I would expect that applying the same impact force to (2) strands of dynamic rope as opposed to (1) strand will make the FF comparison invalid.

Jared Chrysostom wrote:

I don't understand how this would work. If you have (2) 2' legs, you don't have 6' of rope in the system, you have 4'. Also I would expect that applying the same impact force to (2) strands of dynamic rope as opposed to (1) strand will make the FF comparison invalid.

Yes as Kyle pointed out I was too generous. With the 2' leg and additional 2' the load is tied to you have 4' of rope for a 2 foot fall for a FF 0.5 test plus some absorption by the knots (getting us a substantial reduction in forces). Clearly superior than using a sling to construct the anchor.

Delaney Bray-Stone wrote:
Here is a video showing that dyneema is a pretty sketchy option to use as PAS. 20cm falls (well below fall factor 1) result in complete failure. Also, unlike what some people may advise on forums such as this, chain-link daisy chains are even worse than single-sling daisy chains (falining with FF1 falls).

 You should never shock-load a PAS, however it's comforting knowing that lanyards made of dynamic rope will hold even if shock-loaded with a FF2 fall.

The “anchor” in the video is more sketchy than the dyneema tether.  

Kees van der Heiden wrote: A similar situation is a rock tower we have in Belgium, ideal for training beginner multipitch climbers. At the top you have to rappel off the overhanging backside. There are some bolts and a chain, but very low to the ground. A slip while setting up yourself below the chain would easilly result in a factor 1 to 2 fall. Hmmm, we always use dyneema tethers here....

How does a fall BELOW the chain result in a factor 1 to 2 fall?

rockklimber wrote:

How does a fall BELOW the chain result in a factor 1 to 2 fall?

The chain is at your feet. Say, you are particularly clumsy that day and fall down the overhanging wall, while you were standing on the edge, tethered with a dyneema schling. That would be fctor 2, wouldn't it? What I always do in this particular situation is stay low and keep the schling taut. It's also not a really narrow ledge and you can move down a bit until your hips are more or less equal with the chain, so it isn't that bad, but still, gives me creeps now I think about it.

Edit: Oh, I see now my own writing wasn't very precise.