Following recent online discussion stemming from a Rock & Ice article about appropriate abseil knots - and some confusion over certain types of knot and their nicknames - we asked Jack Geldard to clarify the key points...
Climbers often need to tie two ropes together when abseiling. This is so that they can abseil a full rope length and still retrieve the ropes by pulling them down. This article doesn't look at abseiling techniques and anchors (which are very important) but simply looks at the various knots that can be used to tie two ropes together.
There are so many knots and variations of knots out there that it is impossible to cover them all. Instead I am going to focus on the three most common knots used, briefly discuss their strengths and weaknesses, and also point out 1 knot that is too weak to be used safely.
The overhand knot (sometimes known as the euro death knot, the overhand bend or the flat overhand bend) is perhaps the most simple knot commonly used to join two ropes together for abseiling.
This knot is popular due to ease of tying and its flat profile. As with many knots, the overhand knot is weaker when used to join 2 ropes of different diameters, and as the overhand is not super-strong to begin with, it is wise not to reduce its strength any further. Due to its propensity to slip on icy ropes (up to 7cm in one test) it is also wise not to use it in this situation.
The overhand is not recommended (it's not strong enough) for joining pieces of rope that are used as slings or threads that may take a fall. Also if you are abseiling with two people on the rope at one time (counter-balance abseil or a rescue, or just messing about with your mates) keep in mind that you don't have much excess strength with this knot and it might not be the best choice.
Looks like but isn't:
A water knot or a tape knot.
The double overhand knot is just 2 overhand knots next to each other. You tie one, then you tie another hard up against the first.
As with the overhand knot, this still maintains its flat profile against the rock, which is good. It also has increased strength and reduced slippage over the single overhand.
Looks like but isn't:
A double fisherman's knot.
The double fisherman's knot is a classic way of joining two ropes together and for good reason.
A great knot and an obvious choice for tying prussik loops, permanent threads etc. Also very good for abseiling, but can take a minute extra to untie.
Looks like but isn't:
Double overhand knot.
This is the dodgy one. The one that to many people looks safer than the simple overhand knot. But it isn't, it's not as strong. You'll notice it doesn't have any good points listed below.
Too weak to be used. Failing at 30kg in this test.
Looks like but isn't:
A re-threaded figure of eight. The re-threaded figure of eight is a knot that many people use to tie in to the end of the rope for climbing. It is a great and strong knot.
The reason that the figure of eight bend (and the single overhand knot / overhand bend) are not as strong as other knots shown in this article is because they can roll.
These knots roll due to the way that the forces are applied to them. The strands of rope that are taking the weight of the climber both come out of the same side of the knot. It is this that makes them so fast to tie, and also means that the knot is held away from the rock when retrieving, but it is this that makes them weaker.
Interestingly whilst researching this article I came across a knot I hadn't seen before, a version of the double fisherman's knot in 'bend' format, keeping the knot away from the rock during retrieval - you can see it in the 2nd diagram down here: German Knot Test.
You can also use a re-threaded figure of eight knot to tie the ropes together (with the tails coming out of opposite ends of the knot, so not a 'bend') - and it is very strong but takes a while to tie.
Another variation on the double fisherman's knot is to tie a reef knot inbetween the two parts of the double fisherman's knot, and this helps it to come undone after load. In my personal experience, I never have any problem undoing knots after an abseil load, so the extra faff of doing the reef knot wouldn't be worth it to me.
It is often said that a double fisherman's knot is the best for joining two ropes of different diameters. In this test on Rock and Ice all three knots tested were weaker with different diameter ropes.
Which knots do I personally use? For normal abseiling, if the ropes are dry then I use a well-tied, neat, single overhand knot with ample tails (30cm). If I was double loading the ropes with 2 people at once, or if the ropes were icy, I use a double overhand knot. And if I am tying a permanent loop such as a thread or prussik I use a double fisherman's.
One thing to take away from this article?
If using a single overhand, it needs to be neat, tight and not icy. Tighten all 4 strands of the knot and make sure it doesn't have any twists and is 'well dressed'. If in doubt, why not do a double?
About the author: Jack Geldard is a consulting editor at UKClimbing.com. He also works as a climbing instructor and coach, holding the Mountain Instructor Award. He is also a trainee British Mountain Guide.
He has climbed in 5 of the 7 continents, up to a very high level, and enjoys all forms of climbing, from winter alpinism through to summer bouldering. He's still not overly keen on falling off though...
His particular favourite styles of climbing are UK seacliffs, classic Alpinism, and multipitch sport climbs. Or pretty much anywhere sunny.
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