EDK Destructive Testing of Different Diameter Ropes

Brian in SLC wrote: Very common amongst the canyoneering crew (single strand over a pool in a waterfall to set the rap length so folks pop off the rope instead of get tangled in higher water flow). Also, when rappelling with a Gri Gri. Or, using a thin diameter pull cord. Although, folks rappel single strand in canyons all the time seemingly "just because".

Well, not just because. There are a bunch of reasons but there are a few really good ones:
(1)Example, I have a 180'rap but only carry a 200' and 2x100' ropes. Passing a knot is silly and time confusing.

(2) it keep the ropes less tangled until the end. The rope pulls in canyons are often a lot harder than my experience in climbing

(3) it keeps a second strand up top in case something happens like someones hair gets stuck or something else crazy happens down rope. If anybody is up top they don't have to do a haul or descend a weighted rope. They just have to rig the free strand safely and throw the rope or descend.

20 kN wrote: As far as the rest of your quote, I am not following. Yes, the big 11mm fatty will see a much higher load than the 6mm noodle because of the friction differences in the ATC. But I do not see how that creates a scenario that is not analogous of the end-to-end test I performed. Regardless of the load distribution differences, the strands exiting and entering the EDK will see precisely the same load (assuming the knot is not touching anything).

The EDK with ropes of different types and different diameters was thrashed to death 20 years ago on rec.climbing, long before MP existed. Apparently the same questions and issues are still unsettled today.

As I remember:

1) A new small (6-7mm) static and an old fat dynamic rope are the worst combination. Of course, this is the most common combination in practice.

2) In order to stop the rope from creeping on rappel, the fat rope is threaded so the knot stops the creep. This puts a very high percentage of the load on the fat rope. This puts a "shear" force on the knot, promoting it to roll. Since the other strand is lightly loaded, the knot doesn't tighten evenly after the roll. More rolling, and possible failure. (This is why loading the strands equally in your test isn't realistic.)

3) The knot can get stuck in the ring, and the ropes can't be pulled.

4) If you thread the rope the other way, you get the nasty creep problem, and might rap-off the end of the static line.

Anyway, the result of that long discussion is that I use the double Fishermans for ropes of unequal diameter. So what does the UIAA say?

John Byrnes wrote: Anyway, the result of that long discussion is that I use the double Fishermans for ropes of unequal diameter. So what does the UIAA say?

This is something I've ben curious about: is there a point where the EDK is not the preferred knot due to the difference in diameter of the ropes?

mountainproject.com/v/joini…

It is interesting to read your post because, if I recall correctly, no poster presented your point of view.

John Byrnes wrote:So what does the UIAA say?

Nothing.

GLD wrote: Well, not just because. There are a bunch of reasons but there are a few really good ones: (1)Example, I have a 180'rap but only carry a 200' and 2x100' ropes. Passing a knot is silly and time confusing. (2) it keep the ropes less tangled until the end. The rope pulls in canyons are often a lot harder than my experience in climbing (3) it keeps a second strand up top in case something happens like someones hair gets stuck or something else crazy happens down rope. If anybody is up top they don't have to do a haul or descend a weighted rope. They just have to rig the free strand safely and throw the rope or descend.

Not to thread drift too far, but...

1) Sure.
2) Rappelling double strand with an ATC has always worked better for me to keep the strands less tangled. Folks tend to toss the rope bag down and sometimes it ends up in wierd places. That said, I've fed out of a rope bag on descent a fair bit too, especially if its windy.
3) Havin' a spare rope is sweet, but, so is rigging for contingency which almost no one seems to do. Biner or knot block isn't easy to convert to lower for most folks.

I just think knot and/or biner blocks should be the exception, not the rule.

This is something I've ben curious about: is there a point where the EDK is not the preferred knot due to the difference in diameter of the ropes? mountainproject.com/v/joini…;

I don't have any definitive answer. .

The Cowardly Noob wrote: It is interesting to read your post because, if I recall correctly, no poster presented your point of view.

I skimmed that MP thread and it seems most people were focused on knot-strength.

The discussion I referred to was a long time ago and my Alzheimer's is acting up, but I seem to remember that having the knot roll multiple times was the failure mechanism.

I haven't kept up on this since.

John Byrnes wrote: I skimmed that MP thread and it seems most people were focused on knot-strength.

I agree, but that's not really my concern nor the point of the OP.

John Byrnes wrote: T 2) In order to stop the rope from creeping on rappel, the fat rope is threaded so the knot stops the creep. This puts a very high percentage of the load on the fat rope. This puts a "shear" force on the knot, promoting it to roll. Since the other strand is lightly loaded, the knot doesn't tighten evenly after the roll. More rolling, and possible failure. (This is why loading the strands equally in your test isn't realistic.)

Okay, now I follow you. However, that was the point of the second test involving the Fixe ring. In the second test, 100% of the load was placed on the large rope, and the EDK was acting only as a stopper knot. The 6mm was left unaffected and it was not tensioned beyond the initial pretension I placed on it when I tied it.

So are you saying that a light split, of say 90/10, between the 11mm and 6mm is more dangerous than the 100/0 split that I conducted in my second test? If so, I can retest with a light split, but I doubt I will see a change. In the 100/0 split, I tensioned the knot to 800 lbf and the backup overhand was not even tight.

20 kN wrote: I supposed I can. Does anyone ever use that knot for joining raps? I dont think I would be willing to use the DSB for a life-critical application. It seems like a fairly insecure knot, but I dont use it either though.

That's cool, if you can do one, awesome. They work pretty well; maybe not for a rap, but that's not their only app. Did you already run a test on the two-fishie'man?

20 kN wrote: Okay, now I follow you. However, that was the point of the second test involving the Fixe ring. In the second test, 100% of the load was placed on the large rope, and the EDK was acting only as a stopper knot. The 6mm was left unaffected and it was not tensioned beyond the initial pretension I placed on it when I tied it.

Okay, I missed that (sorry). So is that the orange line on the graph? What happens if there's no backup knot? (I'm guessing the backup knot, even without tightening, acts to inhibit rolling.) When I've used the EDK (twin 7.5mm) we did not use any backup knot since we wanted to minimize the possibility of the knot getting stuck.

20 kN wrote:So are you saying that a light split, of say 90/10, between the 11mm and 6mm is more dangerous than the 100/0 split that I conducted in my second test?

It doesn't seem like it would be worse, but that's why we/you test! ;-)

John Wilder wrote:in all the years I've been climbing, I've used the overhand for all raps, usually an 8mm half to a 9 something single.

Alpine climbing? Not a big difference in diameter, and not a static to dynamic either.

John Wilder wrote:I don't actually know anyone who doesn't use it. and I've never heard of the knot rolling in use.

Sorry, this has no bearing on the issue because if the knot were to roll, you'd need two things to "hear of it": 1) To live through it, 2) the rope needs to have been MARKED so you could detect the roll after the fact. Know anyone who marks it?

John Wilder wrote:so while I guess it's fun to talk about how strong it is, in practical terms the knot has been a standard knot for rappelling for probably a decade.

True. However, "It Depends (tm)" still applies. Suppose you're a Big Wall climber descending the East Ledges with a 100lbs pig dangling below you, or while you simul-rap with your partner...

I know this has all been discussed before, many times, just wondering if there is any new information.

I'd really like to see tests without the backup knot :), as I don't use one in practice and the knot rolling is what we really want to examine.

David Appelhans wrote:I'd really like to see tests without the backup knot :), as I don't use one in practice and the knot rolling is what we really want to examine.

Done. I tested the EDK with the 6mm on bottom and with the 6mm on top, both without a backup knot. In both tests, the 6mm broke at the hydraulic cylinder without the knot rolling (although it was close to rolling).

Nice testing!

John, do you tie a backup knot or go with just a single EDK?

Cheers!

Brian in SLC wrote:Nice testing! John, do you tie a backup knot or go with just a single EDK? Cheers!

Hey Brian,

I've only used the EDK with ropes of equal diameter, and don't use a backup.

20kn, are you willing/able to pull test gear that we send to you and/or pay for? I have a friend who uses an EDK to loop his 5.5mm titan-cord cordelette together. Although I am fine with that in a nylon cord, I am curious as to how the EDK fares in this more "slippery" material as compared to the manufacturer recommended triple-fisherman's. I haven't seen anyone test the EDK with this material before.

PM me if possible, thanks.

Fun stuff...

mountainproject.com/v/best-…

Andy P. wrote:20kn, are you willing/able to pull test gear that we send to you and/or pay for? I have a friend who uses an EDK to loop his 5.5mm titan-cord cordelette together. Although I am fine with that in a nylon cord, I am curious as to how the EDK fares in this more "slippery" material as compared to the manufacturer recommended triple-fisherman's. I haven't seen anyone test the EDK with this material before. PM me if possible, thanks.

Sure, PM sent.