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Risk of Yosemite Bowline Knot

Yosemite Bowline knot is one of the most popular variant of Bowline knots used by climbers, notably for the harness tying-in point. However, there is a significant risk for the knot. Basically, a tiny bit of mistying, or even just a bit of wiggle during a course of a day, could cause a serious weakening of the strength of the knot. Here is my video to demonstrate the point — risk of Yosemite Bowline.

Here is the detailed background, followed by some discussion.

The Bowline knot [2018-06016: referring to Asheley's #1 hereafter, unless otherwise mentioned] used to be the most popular knot for climbers for a tying-in point to a harness. Nowadays, a majority of climbers use Figure-of-Eight instead, primarily because Fig-8 is far more foolproof than Bowline. However, there are still a considerable number of climbers who prefer to use Bowline knot or its variants. The Bowline knot (and its variants) have two advantages over Figure-of-Eight, that is, it is easier to untie, which is handy after the knot is heavily loaded (by falls), and is marginally quicker to tie. The major disadvantages are,

  1. Bowline can be undone accidentally, especially in a course of a long day,
  2. Bowline is especially vulnerable for cross-loading,
  3. Bowline is more easily mistied than Figure-of-Eight,
  4. Bowline is more difficult for partners to check (partly because many modern climbers don't know it in the first place),
  5. Bowline is significantly weaker than Figure-of-Eight (the experimental results vary a lot, but as a rule of thumb, Bowline seems to be 10-20% weaker than Figure-of-Eight), though this point is in a vast majority of cases in climbing not a serious concern,
  6. Bowline relies for a part of its strength on an additional stopper knot — in other words, if a stopper knot is not tied (or is undone, as it happens occasionally especially after a prolonged use), it is weaker, and the rope-end may travel through under a high load, even to the point of complete destruction of the knot.
  7. Bowline's stopper knot sits inside the main loop of the knot, and therefore, when it is used as the tie-in point to the harness, the stopper knot touches and catches a harness and/or other things around it all the time, and hence is more likely to get undone than the one with Figure-of-Eight (n.b., Figure-of-Eight knot, unlike Bowline, does not need a stopper knot in the first place for the purpose of extra strength).

Many modern climbers prefer one of its variants to the standard Bowline because they are supposed to address the disadvantages of the Bowline, especially the first one in the above-mentioned list. Note that they all are to some extent more awkward to dress (or set) the knot properly, and hence the caution in tying is still essential. The two most popular variants, apart from Left-hand Bowline (also called Cowboy Bowline, Dutch Marine Bowline, and Winter Bowline, Ashley's #1034½), among climbers are Double-Bowline (Ashley's #1013) and Yosemite Bowline.

Double Bowline has two loops instead of one to thread the (end of the) rope through. It is stronger, and is even easier to untie after the load, than the standard Bowline. However, I do not think it is less likely to come loose than the standard Bowline. Essentially, Double Bowline keeps all the basic principles (and hence cons) of the standard Bowline, but advances some of them. I have heard of a rumour Double-Bowline is pretty popular in Germany as the tie-in knot.

Yosemite Bowline has a follow through of the rope-end via the knot itself. Therefore, when the knot is tightened under a load, it constricts its own tail-end, and so reduces the risk of getting weakened due to lack of (or undone) stopper knot. Personally, I would still recommend you to tie a stopper knot, as I have witnessed the loosened Yosemite Bowline over a course of a day. Also, another advantage is the rope-end is at the outside of the knot and hence is less likely to catch a harness or body, whereas in the standard Bowline or Double Bowline, the rope end and the stopper knot near it touch and catch surrounding things like a harness all the time. Yosemite Bowline seems to be decently popular in the UK and (I guess) US among climbers.

A mention should be given to Edwards Bowline. Edwards Bowline basically adds an extra return to the rope-end to Yosemite Bowline. I have never heard of any quantitative assessment of the knot. However, given its complexity, I guess it is less likely to come undone than even Yosemite Bowline, whereas it is definitely more awkward and slower to tie. I doubt if Edwards Bowline is widely used in the UK, let alone outside (n.b., the name comes from the Cornish climbing legend, the Edwards).

In my blog post a year ago, Cross-loading on knots, I argued Bowline knots are vulnerable to cross-loading, and I also referred to a YouTube video "Yosemite Bowline not safe for climbing" (by "Yosemite Bowline" — seemingly the one-time account), which warns a potential danger of Yosemite Bowline (see also the extensive discussion in the UKC forum).

I have investigated the issue, and presented it in the video in this blog. My conclusion is as follows.

In short, the way Yosemite Bowline rethreads the rope-end in its knot is arguably undoing what Bowline is tied. If Yosemite Bowline is tied correctly and stays as such, there is no such risk. However, if Yosemite Bowline is tied in a (what I call) wrong-handed way, which is akin to the anti-Lapp Knot configuration, then the main Bowline part basically comes undone. The correct and wrong-handed ways are topologically identical, and so by definition they are interchangeable with an external force. In other words, even if Yosemite Bowline is tied correctly first, it can get loose and might transform itself to the wrong-handed configuration over a course of a day of activity by the wearer.

In fact, some argued it is still strong enough even tied wrong-handedly, referring to a single experiment presented in the UKC forum. I am not convinced (a single seemingly non-scientific experiment does not tell much anyway). More importantly, I know well, based on my own experience, even the well-set correct Yosemite Bowline can get loose during a course of a day. After all, Yosemite Bowline is, like any other Bowline variants, more awkward to dress well than the standard Bowline. That means, considering any stopper knots are not reliable for a long term, there is a small chance the rope end may come undone. Once the rope end comes undone, what will happen when loaded is obvious, as demonstrated near the end in my video.

I confess I have been using Yosemite Bowline knot as my harness tying point for well over a decade for indoor or summer single-pitch climbing. The primary reason is it can be untied much more easily than figure-of-eight after taking a fall(s). Falling is a norm especially indoor, and then the ease of untying is a significant advantage, as well as a speedy tying-in, which comes particularly handy in intensive indoor sessions like 4×4. Yosemite Bowline knot has served me well so far.

However, I do not use it during multi-pitch climbing or in winter, because I did notice its tendency to come loose over an extensive period of time, probably after the knot has been rubbed by something surrounding without me noticing. The fact does cast some doubt over its reliability.

I am a strong believer of Murphy's law: Anything that can go wrong will. The tying point of a harness is one of the most fundamental point of safety in climbing and is the most frequently tested one. If I tie in 20 times per week, I will tie in 1000 times per year, and 100,000 times per century (I won't live so long, but it is just for the sake of estimate). That means the acceptable probability of mistying the harness tying-point is smaller than 1 in 10 millions, or 0.00001%.

Now, I don't think Yosemite Bowline is trustable enough for me.