Pothole Escape via Rope Levitation

Perhaps this should be in the “Entertain Me” thread rather than its own, but in any case… back in spring 2015 a small group of us met up in the desert to visit canyons. On one day a canyon presented some sizable potholes. Here’s an early one, picture just for entertainment value, as it turned out to be an easy climb-around.


Later, we came across a small but somewhat nasty hole – swimmer (? memory a little hazy ?), vertical to undercut at water level, which was 6ft down or so. Mike and Robby deployed a new-to-me technique to defeat the problem. I am not sure if they had used it before or devised it on the spot. A potshot was tossed to a decent placement. Mike kept control of the line attached to the potshot and Robby went down in the pot. In the water he got the potshot line under his feet and Mike pulled in the slack until Robby was essentially standing on it kind of like a slackline, but with a “V” shape. Robby was then able to edge up the exit side, hands on pothole wall for balance, as Mike continued to pull in some rope. This kept the line from potshot to Robby’s feet in a fairly optimal orientation, maximizing rock friction, and the V shape was narrow enough that the potshot anchor was seeing a lot less than Robby's full weight. Additionally, I believe Robby was able to pressure the line against the rock lip with a hand as he came up, helping even more. My info above is somewhat secondhand as I was back one curve of the canyon having filled a potshot and awaiting word if more was needed. I did hear the excitement about how well it worked, and it was quick. No pictures of the action, only this one of Robby cleaning up with the little, but deep pothole behind.



In intervening years, I can recall using the technique another time or two. And learning, as should not be surprising at all, that the technique does not work if the “V” gets too wide. Fast forward to fall of 2019 – a group of us are in Heaps in what I understand was fairly low water conditions. In the first section of narrows we came across a fairly deep hole that has a sharp exit lip, perfect for tossing something to escape on. Mark immediately called for using the levitation technique – I think he had a different term for it, and I got the sense he had used it before. I immediately agreed it was a perfect setup. Mark tossed his whole pack as the escape anchor, went down in, and I managed the rope. With the escape anchor so solid, Mark yarded directly on the escape line to make progress up – he was out in 15-20 seconds once initially positioned. Much quicker than attaching ascending gear, and less work than trying to batman it. Pictures:






-john

Great pictures and cool technique. Thanks for sharing.

Slack lining as a canyon technique...awesome!

Cool technique! In case anyone is wondering, I think this should increase the force on the potshot surprisingly little. I ran some numbers through this slackline forces calculator and I was surprised by the results. Forces increase the tighter the line is, but you have to get the sag in the system down to about 2 feet in order to significantly increase the load on the potshot by those numbers. Much tighter than what we see in the photos in this thread. If you keep the sag to 5-6 feet, the force on the potshot is theoretically LESS than if you were to batman up the rope, although the difference is not significant.

Note that I'm not a physicist, and I'm not sure about the effect of having one anchor higher than the other would be. My guess is that it won't be significant in this case, and if anything it would increase the load on the higher anchor and decrease it on the lower one.

Can confirm as a "science person" that having one anchor higher than the other wouldn't change the picture at all. All that matters is the angle. Deflection only matters insofar as it affect the angle between both anchor points. As the bottom of "V" you're standing in approaches the height of the lower anchor the angle of the V is going to get closer to 180 and the closer to 180 you get, the higher your load multiplication.

I dont remember what exactly sparked the idea, but i vaguely recall thinking that if it worked it would be alot faster than pulling out all the ascending gear...so maybe laziness? Seeing that it has worked in other canyon, maybe the technique is best suited for small potholes where you get some utility before the angles get really wide and forces become problematic for humans?

(facepalm)
"... having one anchor higher than the other wouldn't change the picture at all. All that matters is the angle."

Having one anchor higher than the other changes the angle.

If we are comparing the levitation technique to pulling directly on the exit rope, with ideal geometry the load on the exit rope is half the climber's weight, even before being reduced by friction over the edge. (Ideal being where the exit rope goes straight down to the climber's foot, then straight up again to the up-stream anchor/side.) It is essentially a 1:2 mechanical advantage.

There are a lot of friction elements in the system so it is hard to model in a Newtonian way, but when the system is non-flat, it will reduce the load on the exit rope. However, it seems to me the climber makes progress by applying full load to the exit rope, and the levitation is used to hold the climber in position between upward movements, mostly.

Tom

Just wanted to note that the Heaps photo sequence represented an extreme case where the down canyon anchor was so solid the climber could pull on that line. In other cases upward progress was accomplished by the up canyon line being slowly pulled in while the 'climber' balanced against the exit wall/lip.
-john