Half-rope Simul Rappelling

Thank you, David, for this bring this excellent test to light. The results from this test bring some interesting ideas to the table.  I just looked through all of that data you just posted, and it shows that the EDK does indeed get tighter and tighter with each time the knot capsizes. Just from glancing at the data, it looks like every time the knot capsizes it takes about 200 - 300 or so lbs more force for the knot to capsize again.

 Also interesting is that the test showed the EDK roled usually about 3 - 4 times before the rope reached its breaking strength. This may be where Mikey may have gotten the idea that if your EDK roles three times its probably going to stop rolling, because your rope is going to snap soon, and if your EDK roles once you're doing something really really wrong. 

I'm glad you kinda corrected me David.  I went back and looked at Tom Moyers' data (which I hadn't looked at in probably 15 years) and applied that to the statement I made, "a well dressed EDK..." and to the ropes system that are being talked about (ropes that are not dissimilar diameters, i.e. half ropes..).  I only found 3 tests that applied.  I'll just post the data and let others draw their own conclusions.  And I'll edit my post to state that the knot should not only be well dressed but well tensioned. 

Not gonna lie, I skipped all the previous comments cause they didn't seem to have what you needed. Use an atc/act guide/ reverso or similar device, and you can configure the single rope to go through both slots of the device. Yes. Both slots, which ends up giving you more friction than a double rope rappel. If the device is on you facing away from you, put the rope  in top left, out bottom left (just like a normal rap would in the left slot) then work it back in the top right, out the bottom right slot. 99% sure this is what you need. Also 99% sure I did a poor job explaining it to someone who's never seen this technique. In short, put it in the left side of the device. Then put the same rope in the right side. Then use a prussik. 

*edit. Yes ive done it on dry treated 8.1mm ropes. No I didn't die. But obligatory "yer gonna die", cause you know, mountain project. 

We rappel on a single half rope (7.9mm to 8.3mm) routinely. With top rope belay on the second (half rope) line. Using MicroJul or any belay plate (ATC Guide, Reverso, etc). If wearing gloves it is no brainier (with no gloves one needs to add some friction, ref. above). This is the gold "rappeling the first" standard in Russia, Kazakhstan, Kyrgyzstan, etc. The second rappels on both strands (and brings two halves for the next rappel in a case of team of 3+).

Although I would prefer not to rappel on a single  half rope line without top rope belay — the risk of cutting the line is too high (moreover I would prefer not to rappel on any single dynamic rope line if there is any risk of swinging or any loose rock around). Simul rappel on half ropes could be OK if the rock is rock solid and there is no roofs or bulges.

David Kerkeslager wrote:

The knot doesn't get tighter and tighter as it rolls, and it's absolutely not correct that the EDK will only roll 3 times. In these tests, the EDK (noted as the overhand in these tests) rolled 3, 0, 5, 3, 4, 4, and 10 times. More than half the time it rolled more than 3 times. Evidence indicates that the only thing that stops the knot rolling is the rope breaking.

It's disconcerting to me that you're spraying obviously false information, Mikey, and that you believed him without any investigation, Kirtis. I believe you don't intend any harm, but this is a dangerous sport and false information can get people killed. Luckily in this case it's fairly benign, because the evidence indicates that the EDK (flat overhand) is still safe to use despite rolling.

Whao!  Easy David.  Your posts are quite misleading or misinformed.  The link you provided (which I have seen many times) mostly refers to the Flat Figure Eight.  This (hopefully) is becoming know as a deadly knot.  It probably should be called the American Death Knot and should never be used to join ropes for rappel.  Deadly accidents have occurred using it.  

But, the Euro Death Knot/Flat Overhand performs quite differently and requires more than 1000 lbs to roll, as shown in the test data you linked and other tests I've seen.  This is a load nearly impossible to achieve in a normal rappel.  The exceptions in the test were intentionally "sloppy, crossing strands and loose".  Even these took 200 lbs to roll the first time, 400 the second and 1400 to roll a third.  So, yes, after it has rolled once (which is extremely unlikely when properly tied), it takes even more force to get it to roll a second time according to the tests.  Mikey is not wrong.  If you somehow make the knot roll even once (very hard to do with a properly tied knot), it will be harder to get it to roll a second time.

Lurking behind this discussion is a serious issue if you are going to use your ropes as half ropes. If you have to do all kinds of things to add friction to make a single-strand rappel controllable, then unless you are able to add the same friction enhancements to your belays, your belay device will be inadequate for catching hard falls on a single strand, and whether or not you simul rappel is not your most pressing problem.

I don't really agree with that rgold.  Catching a lead fall takes place in less than a second.  And very little rope passes through the brake hand.  And the belayer can grip hard briefly.  

Doing a single strand, double rope rappel takes place over 200 feet of rope and much more time.  Fatigue and heating up of the hand are much more an issue here.  

Kirtis Courkamp wrote:

I love simul rappelling

Red flag #1. I didn't think climbers loved rappelling at all, let alone the more dangerous version of it.

Kirtis Courkamp wrote:

I just looked through all of that data you just posted, and it shows that the EDK does indeed get tighter and tighter with each time the knot capsizes.

To quote the page: "Most of the time, if the tails are long enough, the process of repeated flips stops at some point and the knot cinches tighter and then holds until the rope breaks. In my testing, this often happened just as the knot was about to run out of tail. Since this process is so uncertain, I regard the force at the first flip as the failure load for the knot."

The italics is Moyers', not mine, which seems to be intended to prevent people from pretending the italics word "most" isn't there like you are.

You can draw the conclusions you want from the data, but they aren't the conclusions drawn by the person who did the tests.

Greg D wrote:

Whao!  Easy David.  Your posts are quite misleading or misinformed.  The link you provided (which I have seen many times) mostly refers to the Flat Figure Eight.  This (hopefully) is becoming know as a deadly knot.  It probably should be called the American Death Knot and should never be used to join ropes for rappel.  Deadly accidents have occurred using it. 

If you've seen this many times then surely you've noticed that half the tests are tests of the EDK.

But, the Euro Death Knot/Flat Overhand performs quite differently and requires more than 1000 lbs to roll, as shown in the test data you linked and other tests I've seen.  This is a load nearly impossible to achieve in a normal rappel.

I'm aware. As I said in my post that you quoted, "Luckily in this case it's fairly benign, because the evidence indicates that the EDK (flat overhand) is still safe to use despite rolling."

The exceptions in the test were intentionally "sloppy, crossing strands and loose".  Even these took 200 lbs to roll the first time, 400 the second and 1400 to roll a third.  So, yes, after it has rolled once (which is extremely unlikely when properly tied), it takes even more force to get it to roll a second time according to the tests.  Mikey is not wrong.  If you somehow make the knot roll even once (very hard to do with a properly tied knot), it will be harder to get it to roll a second time.

Mikey claimed it rolls no more than 3 times. In one test it rolled 10 times.

Mikey Schaefer wrote:

 Or just add an overhand knot that is tight up against the EDK on one of the tails.

This is a good method.  I prefer to do it in both tails, together, i.e. stacked EDKs, which I cannot imagine rolling (very scientific, I know), and which rolls around snags just like a single EDK.  

Re: friction, OP seems in earnest, but this still seems troll-y.  When in need of more friction, add more friction.  A bazillion+1 ways.  

David Kerkeslager wrote:

If you've seen this many times then surely you've noticed that half the tests are tests of the EDK.

I'm aware. As I said in my post that you quoted, "Luckily in this case it's fairly benign, because the evidence indicates that the EDK (flat overhand) is still safe to use despite rolling."

Mikey claimed it rolls no more than 3 times. In one test it rolled 10 times.

You conveniently left out the fact that in that specific test it was tied with an 11mm rope and 8mm rope and it was soaking wet. Both of which don't apply to the OP. 

David Kerkeslager wrote:

If you've seen this many times then surely you've noticed that half the tests are tests of the EDK.

I'm aware. As I said in my post that you quoted, "Luckily in this case it's fairly benign, because the evidence indicates that the EDK (flat overhand) is still safe to use despite rolling."

Mikey claimed it rolls no more than 3 times. In one test it rolled 10 times.

News flash:  if you tie knots "sloppy, crossing strands and loose" they might roll.  

Edit to add:  Even the "well dressed and pretensioned - pulled separately on all 4 strands - wet - soaked in bucket ~5 minutes" required 950 lbs to start the roll, the second roll 1300 lbs.  This is your 10 roll friend you are referring to.

Matt Castelli wrote:

99% sure this is what you need. Also 99% sure I did a poor job explaining it to someone who's never seen this technique. In short, put it in the left side of the device. Then put the same rope in the right side. Then use a prussik. 

Interesting technique. Can you post a picture? I can kind of see it in my mind's eye, but I'm not sure if what I think is what you're describing.

Okay, I suppose I was splitting hairs there.

David Kerkeslager wrote:

Mikey claimed it rolls no more than 3 times. In one test it rolled 10 times.

David please show me the test where a well dressed EDK with ropes of the same diameter rolled 10 times?  Maybe you could post up that data for others to review?

Whatever,... if the OP is doing 8 simul-rappels to get down, I personally think it would be worth tying a wicked rugged knot anyways... you're going to be rapping for a long time and not untying the knot so why not.

Ira O wrote:

Whatever,... if the OP is doing 8 simul-rappels to get down, I personally think it would be worth tying a wicked rugged knot anyways... you're going to be rapping for a long time and not untying the knot so why not.

Perhaps, but the beauty of the EDK is that it is less likely to jam when pulling the rope, as opposed to say a double or triple fisherman's, yes?  Seems like the EDK is "wicked rugged" when dressed properly, but maybe I'm missing something?

https://www.petzl.com/US/en/Sport/Belay-devices--descenders/GRIGRI-PLUS

???

It depends on where you rappel....EDK versus a better knot may have no advantage or be worse for snagging as compared to a fisherman's bend etc. An EDK is bulkier to snag in cracks, but does ride over branches and edges better.

TBH, granted a CA bias here...but I have never seen the knot truly be the difference in the rope getting stuck or (k)not. Usually it is rapped around tree branches, a flake or deep in a crack where any knot would be as bad.