TYING TWO ROPES TOGETHER TO ABSEIL
I often get asked why I tie a specific type of knot when tying 2 ropes together to abseil off with. Everyone knows the overhand knot works…
I’m always keen for people to understand “why”, not just accept being shown and told “that’s the knot’ or “the best way to do it” and a number of years ago it got my thinking about why I use the overhand knot and a little bit of research later actually changed my mind of what to use!
CASE STUDY
USA 2002 | 2 UK climbers | 4 ropes
DAY 1 - Climbed 4 pitches, left the ropes in place
DAY 2 - Jugged back up, rain changed their mind and they decided to bail, they abbed to the top of pitch 2
Climber 1 pulled the ropes and was coiling their one of their original climbing ropes
Climber 2 set up the next ab, joined 2 ropes (Both ropes were 60mx10.5mm) together and said “see you at the bottom”. He fell.
“I rushed over and there was nothing there - our ropes had gone, he had gone, the anchor was fine, untouched” It was a fatal accident.
SOME FACTS
Climber 2 was found with the two ropes correctly through his belay device.
The ropes extended about 10 feet "above" him (the other 190 feet being "below" his belay device) and the ends were not tied together.
Throughout the trip they had always been tying ropes together using a fig-eight knot. The only other abseil climber 2 had set up that same day he had used the fig-eight knot with no back up knot on the tails. The knot was neat.
Climber 1 could not see exactly what climber 2 was setting up on that last abseil - he was 10ft or so to his left.
“The fig-eight I refer to is tied as follows: The two ends you want to join are held parallel with the ends "pointing" in the same direction. You grab both ropes together and then tie a regular single fig-eight knot in both ropes at once. What we did NOT use: The only other way that might be confused is when you have the ends pointing in opposite directions. Tie a single fig-eight in one rope then follow this through with the other rope - we did NOT do this. The only plausible explanation of this accident I have come up with is that the knot slipped off the ends.”
SOME HISTORY
From the late '70s, the DOUBLE FISHERMAN'S was one of the knots used - it was hard to undo once you have put a bit of a load on it though, it was also symmetrical - ie it sticks out on all sides
Another being the DOUBLE FIGURE OF EIGHT, (have the ends pointing in opposite directions. Tie a single fig-eight in one rope then follow this through with the other rope) but whilst this was easier to undo than the Double Fisherman's, it was just as likely to get stuck when pulling the ropes.
The same applied to the frankly weird TWO FIGURE OF EIGHTS joined by a SCREWGATE KRAB KNOT.
1990 FIGURE OF EIGHT
(The two ends you want to join are held parallel with the ends "pointing" in the same direction. You grab both ropes together and then tie a regular single fig-eight knot in both ropes at once).
This was always easy to undo, however many times you abbed on it, this was asymmetrical and when the ropes were pulled, the bulk of the knot flipped upright so that only a flat surface was dragged across the rock, with far less likelihood of a snarl up.
I came across some really interesting test results completed by Lyon Equipment based on this very subject
RESULTS
The first thing to note is that when the ropes were soaked and then frozen there was considerably more slippage than when they were dry. Second, and most importantly, in frozen ropes the Figure-of-Eight Knot flipped over itself at 300 Newtons or 30kg. As the weight of a male abseiler plus kit is likely to be around 80kg this is serious cause for concern.
(Test Results from Lyon all the ropes used were brand new 9mm)
Anyway, back on planet Earth, whilst both the FIGURE OF EIGHT and the OVERHAND slipped considerably under pressure, the DOUBLE OVERHAND did less so. Of course all the dry knots held - eventually, but the tests were made with new ropes and with a good tail. Also all the knots were very well tied
A poorly laid knot can considerably worsen the test results. This has been shown by American climber Tom Moyer who conducted numerous tests on various ab knots and published the results on the rec.climbing newsgroup (2). In these he showed that a well-tied overhand knot would eventually roll over itself at 486kg, but that a badly tied version would do the same at 91kg. Bear in mind when considering these figures, that an abseiler abseiling swiftly and jerkily can exert forces of up to 1.6kN, equivalent to 160kg in weight (3).
This is against his “gold standard” of a DOUBLE FISHERMAN'S KNOT which broke the rope (at well over 1000kg) in every case, however sloppily it was tied. Of course we all know that knots shouldn't be tied sloppily, and that long tails should be left, but as we said before, you're cold / wet / tired / frightened / distracted, the weather has turned gnarly/you've run out of daylight/ you've bitten off more than you can chew etc, or maybe you've just been distracted by the attractive girl / boy sharing a stance with you… Whatever the reason, we all tie our knots less than perfectly on occasions, so it makes sense to use the safest knot available. Well almost. Actually the safest knot by far would seem to be the DOUBLE FISHERMAN'S, but this as stated above is hard to undo and easily jams on rock nubbins etc. As a jammed ab rope may require some serious and potentially dangerous antics to free it, this only means the DOUBLE FISHERMAN'S is the safest if it does not jam.
As a result of all these findings the DOUBLE OVERHAND is perhaps the best knot (if not the safest) to use when joining two ropes together for abseiling. It is very easy to tie, it is asymmetric and thus less likely to get jammed, it slips less under load, and it seems significantly less likely to flip over or come undone accidentally than the alternatives. Moreover, each time you tie it, to get the two component knots cinched up tight together, you have to think about what you are doing. This in itself is a significant safety factor as it should lead to you laying the knot correctly even if you are tired.
It’s interesting that an extra overhand knot takes an additional few seconds to tie and provides additional security, so why wouldn’t you…