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bluefoxicy
Apr 15, 2012, 11:31 PM
Views: 14227
Registered: Apr 1, 2012
Posts: 21
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The gym I hang in refuses the yosimite bowline as a valid climbing knot. It's pretty much my favorite knot for the general purpose (that being of securing something with a loop).
The obvious reason I favor the Yosimite bowline is because it's easy to tie, although I'm told it's hard to verify. That aside, there are more technical reasons I want to put up here to hear some other thoughts on this.
Let's start with the knots that the gym allows.
First off, they allow the figure 8 retrace knot as a valid climbing knot. I'll likely use this in all cases since yosimite bowline is not allowed. It takes longer to tie and is harder to slide more slack through for a back-up knot, but it's a very secure knot. The Figure 8 retrace knot is an extremely secure knot, self-tightening under any direction of load, with lots of internal friction and clamping against everything.
They also allow the double bowline for lead climbing. Lead climbing carries extra risk for longer falls, so a secure knot is critical.
In the Bowline, there is a loop (formed first), a bight (formed by running the free end up through the loop, around the work end, and back down through the loop), and a free end pointing inside. The Bowline relies on friction between the bight and the loop: the free end can easily slip back, but unless it is negatively loaded (pushed back) it probably won't. Load on the bight from the opposite end (the end loaded by a falling climber) will clamp the bight around the work end of the knot.
That means the Bowline is theoretically pretty secure, and in reality it performs well. The double bowline, accepted by the climbing gym, is more secure because of increased frictional force by a second turn of the loop.
Claiming that the double bowline is necessary for improved security of the knot stands out to me: this claim asserts that the friction of the loop to hold the free end in place is significant and important.
That's where I have a problem.
Let's reference here:
The Yosemite bowline finishes a normal bowline by first looping the free end behind the right side of the working loop. Then it comes around, behind the entire knot, and then up through the bight. Tightening the knot not only adds extra friction to the working end of the work loop, but also clamps the free end at the critical position--the Yosimite Bowline acts as its own back-up knot! On top of this, you also proceed to tie a regular back-up knot, of course; but it still stands that the Yosimite bowline clamps its free end firmly, providing a much more secure hold than a Bowline or Double Bowline.
To summarize briefly:
- the bowline and double bowline clamp the final bight around the work end when under load, providing a high amount of friction to prevent the free end from sliding out--the free end is doing the clamping, not being clamped. If the frictional forces fail during this loading--an extremely unlikely event--the knot would immediately come undone.
- The Yosemite finish puts two more high-friction bends on the free end, then clamps it under what is the final bight in a regular bowline. When loaded in the same way, the Yosimite bowline clamps down hard on the free end to hold it in place. If the frictional forces preventing the bight from sliding were to fail during this clamping, the free end would be held via clamping force (and more friction at 2 subsequent points), simply tightening the knot.
Because of this, I'm inclined to NOT use the double bowline when climbing and stick with the double figure 8, which they allow and which is also a self-tightening, extremely secure knot.
(Yes, I'm aware that clamping works via friction; but clamping generates friction from at least two ends and also deforms the rope such that an increased amount of energy would be needed beyond simply overcoming friction. The rope segment that's clamping down is experiencing at best half as much friction as what it clamps.)
Is this insane? Is it a failed assessment that the Double Bowline is fundamentally less secure than a Double 8 or a Yosimite? I understand that it's probably adequate for the task--obviously either history shows or everyone involved in climbing is too stupid to notice people keep dying from failed double bowlines, and the later case seems unlikely--but it's not a decision between something ridiculously more difficult and something with a much lower cost associated. The trade-off using a Double 8 versus a Double bowline is effectively nil, so I'd rather stick with what's more secure.
(This post was edited by bluefoxicy on Apr 15, 2012, 11:32 PM)
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Post edited by bluefoxicy
() on Apr 15, 2012, 11:32 PM
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