UKH

I saw the picture below on Petzl's Facebook page today and noticed that they don't approve of using an overhand (European Death) knot for joining ab ropes of differing diameter.

Is there any particular reason for this (other than abbing on ropes of differing diameter is a bad idea in general)?

Aside from different diameter ropes,

Do the origins of the term 'European Death Knot' come from American climbers who 'rap' using a triple fisherman's knot finished with a quadruple stopper, just in case.

EDK all the way!

The knot can roll out!

Abbing on different diameter ropes can present issues with varying stretch.

There are ways to tie different ropes together with variations of the EDK , maintaining the advantage of a flat edge and stopping any ability to roll out.

Half Gibbs Offset Bend all the way!

I think the problem is that it looks pathetic.

In the Alps in the 70s, you could always tell if a British or Euro climber had been the last to use an abseil point. The Brit would tell their partner, " it was  tied with that f ing knot again, but its OK now, I retied it with a double fishermans."

I believe there is some concern that very differing rope diameters will cause the knot to roll sooner.

The only testing I have seen is here: https://user.xmission.com/~tmoyer/testing/EDK.html which does show a low force for the initial roll on mismatched diameters.

Abbing on ropes of different diameter is not a bad idea per se, but it does introduce a new factor to take into consideration, which is that the thinner rope will usually pass through the belay plate more readily than the thicker one. This means that, during the abseil, the joining knot will tend to creep either down (if you've threaded the thinner rope through the anchor) or up (if you've threaded the thicker one.) Sometimes the knot can move several metres or more and potentially not leave enough of one rope to reach the ground or the next anchor. It's generally best practice to thread the thicker rope when the two are notably different, even though this makes it heavier and harder to pull the ropes afterwards, as that way the knot will stop when it reaches the anchor and will creep up no more.

I think the Petzl diagram may be suggesting an increased likelihood of tail slippage through the knot if one rope is notably thinner; however, this can easily be prevented simply by tying a second overhand in the two tails, right up against the first, which will then be only marginally more likely to jam (and still much less likely than a double fisherman's).

Don't Americans generally climb on a single and use a tag line when abbing? The tag line usually being of a much thinner diameter and necessitating the use of bucketloads of knots and krabs to make retrieval safe? Our wacky idea of using matching ropes that only require a single sensible knot has confused them into thinking it's dangerous, maybe. 

My understanding is that that term EDK originally arose from the practice (which may or may not have originated in Europe) of tying the ropes together with a figure of eight knot, rather than an overhand.  It was subsequently demonstrated that a figure of eight knot is almost certainly not as good a knot to use for joining abseil ropes as an ordinary overhand because (a) the Fo8 tends to roll/capsize at significantly lower loads than the overhand when put under tension, as is almost impossible to avoid when abseiling, and (b) when the Fo8 does roll, it 'eats' more of the tails than the smaller overhand does i.e. it would take fewer rolls/capsizes for the Fo8 to roll right off the ends of the tails (and remember that the Fo8 is more likely to roll anyway).

Over time the term EDK seemed to become commonly used for any knot used to join ab ropes that wasn't a double fisherman's.  This was despite a couple of clear advantages that the overhand has over the fisherman's: (i) it's an asymmetrical knot, so less likely to get caught up on stuff when the ab ropes are being pulled, and (ii) it's easier to untie at the end of an abseil than the fisherman's, which tends to jam up pretty tight once loaded (although this latter characteristic may have been a factor in some people not trusting the overhand).

Added security for ab ropes joined with one overhand knot can be provided by tying a second overhand knot snug up against the first one, and this is frequently recommended (see first link below).

None of the above takes into account the pros and/or cons of an overhand tied on ropes of dissimilar diameters, though it is worth noting that the tabular test results in the second link below do include two tests of such a knot (note, though, that in addition to the diameters of the two ropes being different, one rope was dynamic while the other, narrower one was static).

References:

https://www.needlesports.com/Information/Need-Advice/Abseil-Knots

https://user.xmission.com/~tmoyer/testing/EDK.html

One krab and a clove hitch is hardly a bucketload. I’m a convert now for alpine  climbing.

What is the advantage here over just adding a second knot as per john arran?

Tagline is 5-6mm. Super light. I abseil on the lead rope with Grigri. Which I prefer to  prusiks, extended set up etc. 

Potential downside is that the krab might possibly be more likely to catch on recovery. Also the tagline can be hard to pull if there is a lot of friction in the system. This can be solved by using  micro/nano traxion to pull with. 
I’m not advocating anyone use this system but it works for me and partners.

Many years ago someone recommended a variation of the double fisherman's to me which is to tie a reef knot and then a single fisherman with three turns on each end. Used this ever since, feels 'bombproof' (to me), definitely has the advantage of being much easier to undo, but the still problem of the rope snagging, but find careful rigging mitigates the problem some (but definitely not all!) of the time.

Never felt fully comfortable abbing off the EDK even though done it plenty of times - usually on someone else ropes, and you see it used all over the Alps. I think the key is having very long tails.  In an ideal world would take a single plus a pair of half ropes with me on trips, but it really eats up your hold allowance and wouldn't like to risk taking a rope as cabin luggage these days, in case it got confiscated.  Compromise by taking a triple rated and a half rope on Alpine trips which gives several climbing / mountaineering options, including being able to tie them together, as both very similar diameters.  Wouldn't use the triple on its own for cragging though.

I think it's more to do with slippage than the knot rolling. 

A rope will have something similar to a "minimum bend radius" proportional to its thickness. not quite as fixed a physical property as say bending steel bars, but the concept is the same. A thick cord can't tighten down so we'll onto something that's significantly thinner than itself. 

Obviously there's no hard rule for where to draw the line. I wouldn't get in a flap joining 9.0 and 9.5 mm

If you really want to get your double fisherman's tight, then I recommend tying a few ropes together and stretching them across a valley (Dovedale's good) or quarry before going for a little trip across the rope.

Took absolutely ages to get all the knots undone but the looks from non-climbers when they suddenly became aware that somebody was directly above them were one of the things that made it worthwhile.

Not too long tails, people have rigged onto the tails with fatal effect before now. Enough tail so you can see the end clearly is enough. A second overhand snug against the first is enough to prevent rolling.

I wondered aboit this.  I did an experiment at the wall using a length of 6mm accessory cord tied to a fat 10.5mm old school single using a single overhand.  It was fine.  Good enough to give me confidence to use a single overhand for only slightly different diameter ropes.

I'd be asking myself why I didn't feel comfortable with something that's best practice and that has advantages that you yourself admit to recognising. It does sound like you're wary of using an overhand simply because it looks insubstantial. In which case, surely tying a second overhand snug up against the first would mitigate your fears without adding as much rope snagging potential as is inherent in the double fisherman's. I do like the reef knot idea in the middle of the double fisherman's though, to ease untying. I used to use that method myself for a while until I realised that the overhand was an altogether better system again.

https://www.andy-kirkpatrick.com/blog/view/rappel-knots-1

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p.s. In reply to GarethSL:

Yes!!

EDK every time. 18 inch tails, pull all 4 lines tight first. They are also more likely to lie flat when pulling the rope through and snag less. 

Another possibility is to take one of the 2 ends of rope and wrap it around the knot and then back out through the middle. This gives a smaller knot than the 2 overhands and also eliminates the possibility of the knot rolling.

I think it depends on the difference between the rope diameters.

I've a 9mm triple and 8.6mm half and it seems fine with an EDK on abseils. Visually the two ropes look the same diameter. I make sure there is a decent tail and all 4 strands are nice and snug. 

Having read this thread I'll try to make sure the 8.6mm is on the bottom of the knot in future though.

When I bought the triple I tried to get something as close as possible to the diameter of the half rope. The triple has been amazing as we can now take a half and a triple (rather than 2 halfs and a long single) and that covers pretty much everything for trips to the Alps. 

It really is a knot worth knowing isn't it (fine technically bend) and I'm glad my partner showed it to me. Of course it probably shouldn't be used exclusively as for some situations others may better.

All the advantages of the flattened offset overhand whilst only marginally bigger. Has the caveat of a reduced risk of rolling and works well with differing diameter ropes. All for one extra pass of one end (as I think Alta Via is also trying to explain).

As Andy writes, "perhaps the knot we should all be using."

I'm sure I remember some testing being done and a poorly dressed overhand can roll on 90kg but a properly dressed one is closer to 200kg.

And then how do you do it at the next anchor down? With the half/doubles you can just alternate the rope to pull. I guess with the EDK tagline and two slot belay plate method you could also alternate between the ideal (pull tag line) and the less ideal (pull rope), is this what people do in practice?

Anyone know does it matter if it's the thick or the thin that goes round twice on the half gibbs?

What is meant by a knot "rolling"?

My googling just gives me stuff about foam rolling knots in muscles!

There used to be some links to videos within the Needlesports pages on this:

https://www.needlesports.com/Information/Need-Advice/Abseil-Knots

I'm not sure whether there still are - possibly on some of the things they link to?

One thing they've linked to does at least seem to have a bit more of a detailed description of what they mean by the term roll (or flip) but it's a bit hard to visualise. https://user.xmission.com/~tmoyer/testing/EDK.html

youtube.com/watch?v=QGqGlFc3oFs&

note how the overhand and figure of eight begin to "roll" under load.

Thanks. I think I get the idea now.

I would tie as is recommended with the overhand. With the thinner rope on the "inside" or "bottom" of the knot - this is because the thinner rope has to roll itself over the thicker rope first before the knot begins to roll.

http://www.supertopo.com/photos/18/71/308671_1199_XL.jpg

That would mean the order of the gibbs would be thin-thick-thin, with the thinner rope taking the extra run through the knot.

https://www.ukclimbing.com/articles/skills/abseil_knots_explained-8792

You're likely half referring to this. The bad knot was rubbish, hardly news. The good knot failed at 635kgs.

This rings more true with stuff I've test long ago using Lyon Equipment's set up when they lived in Dent. 

There are stronger knots for joining two ropes, but they aren't necessarily the best for abseiling ropes for many reasons. 

I meant a much longer tail than you would generally leave after tying other types of knot.  I think the recommendation is to tie a single overhand knot a minimum of half metre down the ropes and to leave at least 25cm tails on a double knot.

As with any abseil, buddy check everything twice, every time, before committing!

I believe they showed that an O/H knot could roll at 800kg or something but doubling up stopped even this highly unlikely scenario occurring.

Can't disagree, that was put off by the casual way the overhand knot was used (without any real technical explanation) when first saw it many years ago now, when the test reports, articles, comments etc referred to here weren't available, so carried on with what knew best.  On reflection and reading up, I must admit do like the look of the double overhand, so will try it next time.

The overhand knot is not infallible though, one of worst jammed ropes ever seen was a Czech pair abeiling off one of the Cinque Torri towers, just before a storm came in.  They had to abandon it until after storm, then do another route in order to retrieve it.

Possibly stating the obvious but for a buddy check to be reliable both climbers should use or be familiar with a knot. For example I wouldn't be much use checking variations on the overhand other than ensuring the basic form was tied with the thinner rope unlikely to roll over the thicker. 

I was first shown the EDK by American climbers in Tuolumne in 1999. They said they always used it becuase it was less likely to be snagged and jokingly referred to it as the European Death Knot.

The other thing is that, at the end of a long day, in the semi-dark when you just want to get off the hill and your focus is waning, an overhand (or two) is about as simple as it gets. 

I don't know what Petzl's problem is, but there has been a lot of discussion and various tests about this for years now., the consensus being that the EDK is OK with different diameters. 

I think the best solution is one I posted six years ago on MP; have a look at https://www.mountainproject.com/forum/topic/115342090/is-the-overhandedk-no.... For uneven diameter ropes, thinner rope should be the bottom turn of the knot and the extra tuck performed with the thinner strand.  In the diagram (from Mark Gommers) in my post, the thinner rope would be the blue strand.

The failure mode of the EDK is to have the bottom loop roll over the knot, and the extra tuck anchors that bottom loop and keeps it from expanding enough to roll over the bigger loop just above. The knot is still compacts

As an aside, It seems that the US guiding community can't tolerate gallows humor and opposes the EDK terminology---maybe because it frightens their clients?  So many texts and discussions refer to the EDK as a "flat overhand," which is pretty silly, as there is nothing flat about it and it is not flatter than other knots.  Much better but not widely adopted terminology would be to call it an offset overhand (the two load strands come out of the same side of the knot), as opposed to an inline overhand, (the two load strands come out of opposite sides of the knot). The inline overhand goes by the name of "ring bend" and "water knot" in the US.

To be fair: Petzl show significant dia difference with their "!" symbol; not their skull and bones instant terminal death warning. 

AFAIK... it's the thin one to get the extra turn