Failure of Smooth Operator to pull on extended anchor in Pandora’s Box.

Yesterday while descending Pandora’s Box we stuck a rope while using a Smooth Operator on the second rappel. We’ve been using this particular setup for years (and hundreds of rappels) without incident so for us this failure was significant.

Our gear/setup:

To pull the Smooth Operator we use a 2mm Dyneema cord (arborist throw line). We like how lightweight and compactable it is. We can squeeze 300ft into a tiny bag that can easily hang off of a harness or fit in pack. We also use 2 carabineers tied together with cordage of some kind (basically a homemade quick draw) to lock off the system for all but the last person.

What Happened:

The anchor for the second rappel in Pandora’s Box is webbing from a log jam extended approximately 1 foot over the ledge. The rappel is generally 2 stage but optionally done as 2 separate rappels if there is material for a deadman in the middle section. The rappel is notorious for sticking ropes which is why the anchor is extended so far over the ledge.

We opted to rig our fiddlestick on the established anchor but to shorten it for a “courtesy” for everybody but the last person. The drawback of this decision is we weren’t able to witness how the Smooth Operator would “float” prior to the last person which is a huge benefit to using the Smooth Operator over other similar devices.

The first 4 in our group went over without incident. I was second to last and before I went I mentioned to the last man that the stone knot looked unusual (more long and skinny than short and fat). The stone knot being dressed incorrectly could have been the source of our challenges.

Being second to last it was my job to manage the pull cord. I opted to stop in the middle stage of the rappel in order to more safely belay the last man and also manage the pull cord. I threw the pull cord/bag down the second stage to be secured RDC in an ideal pulling position. The last person made the awkward transition, pulled the safety “quickdraw” and set the smooth operator in what looked like a free floating, ideal position. Both of us observed that the pull cord was in an ideal position before rappelling down the second stage.

Our problems began when we tried to pull the cord from the RDC position. Wouldn’t budge. We then moved the pull cord LDC. LDC put the pull cord in much more contact with rock but gave us more options to get leverage to pull. Wouldn’t budge. Eventually one of us stemmed up into the canyon, tied into the pull cord and fully weighted it. Wouldn’t budge. On the next try 2 of us weighted the pull cord for a combined 350 lbs. Snap! The pull cord broke and we tumbled to the ground. What was left of the cord snapped back out of reach. The cord should have been able to hold 1000 lbs so it either isn’t as strong as rated or was cut on some sharp rock from the less than ideal LDC pull spot.

To resolve the situation one of our group ascended all the way back up to the Smooth Operator to find the pull cord wrapped around the stick (photo attached). He unwrapped it (leaving the original stone knot), rappelled down and pulled (with much effort) the stick from the middle station. He then used the deadman from the middle station to finish the pitch.

We aren’t sure exactly what went wrong.

The stone knot could have been incorrectly dressed and after weighting the rope made the stick impossible to pull.

The pull cord could have somehow twisted around the stick when we moved LDC to try a second pull. Or the pull cord could have looped around the stick from the recoil when the cord broke.

Photos:

The first photo is a closeup of the stick after ascending the rope to find the pull cord looped over the stick.

The second photo is of the rigging with the Smooth Operator locked off (with "quickdraw") and the "courtesy" shortening of the anchor in place.

[QUOTE="Zach Olson, post: 114830, member: 5486]

Our problems began when we tried to pull the cord from the RDC position. Wouldn’t budge. We then moved the pull cord LDC. LDC put the pull cord in much more contact with rock but gave us more options to get leverage to pull. Wouldn’t budge. Eventually one of us stemmed up into the canyon, tied into the pull cord and fully weighted it. Wouldn’t budge. On the next try 2 of us weighted the pull cord for a combined 350 lbs. Snap! The pull cord broke and we tumbled to the ground. What was left of the cord snapped back out of reach. The cord should have been able to hold 1000 lbs so it either isn’t as strong as rated or was cut on some sharp rock from the less than ideal LDC pull spot.[/QUOTE]

Additionally, from my position down canyon, the move that broke the cord was fairly dynamic. One person tied into the cord, while stemmed 5ft off the canyon floor, with a second person below. Both loaded the pull cord dynamically, by dropping to the floor level resulting in a break. The cord also contoured around two points of contact.

I think it is also possible there was rotational tension built up in the webbing, resulting in the stick spinning clockwise in place, and entangling the cord.

I love the concept of courtesy loops being used in webbing to reduce rope grooving, and the chance of sticking a rope. I also like the idea of using said courtesy loop as a placement point for toggle type devices. Keeping the device in a controlled area, allowing a comfortable transition to rappel, while still leaving the single or double rope straight pull function.

We have done thousands of pulls on this cord without a break, but it happened, so we need to iron out why.

Thoughts?

The 2mm Dyneema breaking with only 350 lbs doesn't surprise me. That thin cord is probably easily weakened by nicks and knots along its length. Did you inspect the break location for a possible cause?

It does look like the stick rotated and snagged the pull cord. However, from looking at the close up picture of the stick and stone knot, the rotation must have been counter-clockwise. Otherwise, I don't think you can get the wraps we see. But the recoil hypothesis could also be valid.

The stick rotation has always bothered me. Mostly because we always work hard to get the stick to "float" and have to watch our hard work destroyed by the rotation. I'm sure your last man was watching the stick during the first rappels to verify that the rotation was not a problem.

I'm always most comfortable when someone at the bottom pulls all the slack out of the pull cord before the last man removes the safety. This way no big loops of loose cord are available to get snagged by a twisting stick.

Another hypothesis could be that the last man, when removing the safety quick-draw, accidentally hooked the pull cord around the stick.

Comments

a) sometimes the stone knot grabs the toggle harder than expected
b) acute rub points should (ideally) be managed in ways other than brute force
c) 2mm Dyneema is generally inadequate as a release cord, in terms of strength, and abrasion/cut resistance

This could likely have been prevented by breaking up the rap into stages, or (maybe) by using a more-robust release line (e.g. rope) to address the acute rub points. The first tactic is ethically preferable. As others mentioned, it is unsurprising that the 2mm cord broke in the given situation.

@Zach Olson what was the specific brand/model on the 2mm cord and how was it attached to the toggle?

p.s. I assume the cord wrapping around the toggle/stone knot occurred after the cord snapped

p.s.s. Spelling out what likely happened: The stone knot grabbed the toggle unusually hard, making for a difficult release. The release cord broke because it was: running over multiple rub points + overloaded + (possibly) weakened from prior use.

I know how much you guys used that pull. Can we toss in fatigue wear as a possibility? Obviously in this scenario there was no way that the stick was going to pull with the pull cord "locking" itself off around the stick. Even a 6mm pull would have just clinch it tighter.


To add to this:

We (was with Tirrus) snapped my 2mm Dyneema that was relatively new over a lip with some iron sticking up on it. Surprisingly it broke very easily and we decided it was likely a brand issue compared to the use Tirrus was seeing with his without any signs of failure. Mine was visibly different from his though I thought I ordered it from the same company.

I personally switched to Atwood's cord. It requires a slightly bigger bag and is slightly heavier. Probably the heaviest I would go for this application. Too much weight on the pull line leads to more possibility of that weight pulling the stick out on longer raps when unweighted.

I agree with your most likely summation of what happened. It was probably the combination of several factors (improperly dressed stone, dynamic force applied to pull cord over abrasion points).

The 2mm dyneema is obviously weaker than a rope as a pull cord but given how long this system has worked for us I'm not going to be running out to buy a 6mm pull cord anytime soon. I think learning from this incident by changing some tactics in the future will be adequate.

I've been personally using my cord for about 4 years and am definitely due for a replacement but that wasn't the cord that broke. The cord that broke was pretty new and had only been in a few canyons. I think the line is secured to the smooth operator with a figure 8 follow through.

Below is a link to the cord we've been using:

https://www.treestuff.com/store/cat...QNE6PRbAHXG9aYvU__kThnn4L_qLl_DrElq7aw#detail

Also a link to Atwood's cord (I might be purchasing some of this soon like CRNPRES):

https://atwoodgear.com/collections/...rT1JO_paDNu2b7lRPyP-4lELN5AVXgxMOONn3AP7O9AMA

Would you share those ideas for change with us?

I'll start by saying I have little experience with using a toggle. Looking at the picture it appears the stone knot was not dressed.
So like Hank was suggestion it gripped extra hard. Look at the close up the right strand is loaded on the toggle.
Just my 2 cents


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Sure thing.

1. If I see a knot that looks questionable, different, or funky take the initiative and time to fix it instead of being complacent.

2. Rethink using the Smooth Operator on anchors extended far over ledges. Our goal is to use this technique to reduce rope grooving but there are clearly trade offs with observing stick behavior prior to the last person at risk. Maybe we just err on the side of grooving the rock in the future. It's going to be a judgement call depending on each situation.

3. Learning the limits of the equipment through this situation we can change our plan if the pitch involves pulling around corners. We've always tried to mitigate pulling around corners but maybe this incident will push us in a more conservative direction.

Hank I think we disagree on the fundamental nature of the incident.

Based on your evaluation that the cord is "generally inadequate as a release cord" you assess the problem is an equipment issue. Alternatively, I see human error using gear that performs well when used correctly.

I do enjoy a lively discussion of nerdy rope stuff on here though

No disagreement here. From my POV, the main factor was the decision to not split the rap into 2 separately-anchored stages. The 1.8mm cord mention was intended as more of a general aside, but I didn't make that clear at all.

The way the pull cord is wrapped around the stick (or toggle) it is locked off. This could have happen during ascending but if it was like this during the pull you could not pull the stick out no matter how hard you pull. Pulling would clinch down on the stick with the twist/loop. It looks like the stick spun (which is common) and unfortanately it trapped the stick (not having the courtesy start may have caught this behavior or may not have).

Something has to break anchor, stick, 8.3 canyonfire, and in this case the weakest link the pull cord!! I would assume the right strand is so much tighter at this point in time because someone just jugged the rope and the weight on and off pulled it tighter than normal (i think this would still pull if it was not locked off). Not saying the 2mm cord is strong enough (i switched away from it) but even with a 6mm locked off like that its not going to pull the stick unless its untangled first.

The Stone Knot looks just fine to me. It was flat - which is the way I like them.

You did not indicate how many people were in your party, so how many people rapped on the Stick before the last person. I like to re-adjust the knot when going last in order to loosen it to improve the pull. Especially if the pull is likely to be difficult.

We have been using the 3mm Amsteel, the same as Taylor (Atwood) is selling. I would not go smaller because I worry about it abrading and cutting across an edge or surface.

I do not think we need to theorize on why the cord cut. It was crossing two edges. The rock is pretty abrasive. And you put substantial force on it several times. Amsteel (Dyneema) is strong but not particularly abrasion resistant. Cut resistant to some knives, not to others.

Probably woulda been a better idea to jug the short 2nd stage and try the pull from the chamber after the first time it did not pull. Hindsight-20-20, of course.

Tom

It's so rare that pulling out the toggle is the hard part. It's almost always pulling out the stone knot when there is an issue.

In this case, the last rappeller failed to ensure there was no way the pull cord could wrap around the toggle and it did.

The cord cut was just from using a tiny cord. Usually 350 lbs is plenty of strength to pull out a toggle. But I don't know that you could have gotten that one out even if you had used a 9 mm rope (although it likely would not have wrapped around it like that.)

If you were using a duber dropper you would never have run into this situation.

Did a small amount of testing of stone knot dressing and placement on the toggle to see how it affected the force necessary to pull. Specifically I was interested in two variables:
- knot dressing such that 2-strand side is flat (photo 1), vs. the 2-strand side bending over the toggle edges (photo 2)
- knot position - nearer the pull side (~ 1/3 of toggle on pull side) vs. nearer the free end (~ 2/3 of toggle on the pull side)





My test setup was free-hanging - toggle in open air (photo below). The rap rope weight was simulated by hanging the rope and its bag on the rap line. For measuring pull force I used a pack hanging off the toggle pull line to which I could add weight (bricks) incrementally. After rigging the knot I loaded the rap line with my body weight for 10-20 seconds to set it. The rope was 8mm Grand (Atwood), which is a fairly supple rope. I think pull issues are more likely with smaller diameter easy-handling ropes.



I did a few tests with each configuration, and here were the avg/max pull forces:

flat, near pull: 37lb / 37lb
flat, near free: 42lb / 53lb (note: dressed knot particularly tight on one iteration)
bent, near pull: 63lb / 75+lb (note: ran out of pack space for more bricks at 75lb)
bent, near free: 63lb / 75+lb (note: ran out of pack space for more bricks at 75lb)

With this simplistic test, knot position seemed to have little effect. We've theorized that placing knot nearer the free end of the toggle should make the pull easier since it provides more leverage, but that didn't show in this free-hanging test. It may be more of a factor when the knot is resting against rock.

On the other hand, the knot dressing style did appear to impact the pull force. Maybe enough such that when combined with cord stretch and pulling around rock edges, could lead to issues. (?) Perhaps worthy of further testing.

I have added this post to this thread as I noticed the stone knot was dressed such that the 2-strand side bent over the toggle edges, and appeared to be dressed very tightly.

-john

Excellent! That is a substantial difference!

200 foot rope?

Tom

160' (until recently I thought it was 200', but that's another story), but the rig was free-hanging which is rare in the field, and included the rope bag weight.
-john