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How strong is your knot?

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Re: How strong is your knot?

#121

Post by blacksmith_tb »

Balgair wrote: post #114

Just a plug for Clifford Ashley, the god-father of knots and their tying. His book has some of my favorite knots in it and is a joy to have received as a gift when I was younger. His stopper knot is a pretty cool one. https://en.wikipedia.org/wiki/The_Ashley_Book_of_Knots

ABOK is a wonderful book, but I wouldn't recommend it to someone who just wants to learn a few more knots - books by Geoffrey Budworth or Des Pawson are much clearer in terms of how to tie (though far less encyclopedic than Ashley).

Re: How strong is your knot?

#122

Post by ben7799 »

I was highly disappointed.. this article had so much potential.

Really it's great but it was such a let down to only see an animation of one knot with their special cord in the article.. I was really hoping to see animations/gifs of a bunch of interesting knots!

Re: How strong is your knot?

#123

Post by kragen »

mightybyte wrote: post #98
alister wrote: post #65

I have a knot problem that I think pretty much everyone has encountered. How do you tie a bundle of branches or a cardboard box or something compressible as tightly as possible? The first way everyone tries is to cross the rope like you would for shoelaces, then putting pressure on the crossed rope with your finger, and trying to cross the ends of the rope with your one free hand to finish the knot. Inevitably the kn…

I second the suggestion of a trucker's hitch. A ratcheting knot can be useful in this situation, but IMO what you're really after is a mechanical advantage. The trucker's hitch gives you a mechanical advantage by using a loop in the rope as a pulley. There are a number of ways to make the loop and it doesn't really matter which one you use. This video gives a pretty nice explanation. https://www.youtube.com/watch?v=r…

Whoa, I had no idea the trucker's hitch was a real knot; I thought it was an Ylvis joke.

Re: How strong is your knot?

#124

Post by kragen »

dgacmu wrote: post #37
tick_tock_tick wrote: post #3

I'd love them to do a break down on common knots as I trust my life to figure 8s and fisherman knots pretty regularly.

Look for older reports from rec.climbing. For example: http://canyoncollective.com/threads/some-knot-testing-data.7... And https://user.xmission.com/~tmoyer/testing/EDK.html Some of the testing folks at black diamond did a bunch of tests when we were all jabbering about knot safety about 20 years ago. Kinda sad the old posts are getting so hard to find!

We need a search engine focused on organizing the world's information and making it accessible and useful, instead of advertising.

Re: How strong is your knot?

#125

Post by dragontamer »

kerkeslager wrote: post #104
KirinDave wrote: post #77

Earlier quoted context omitted.

Don't solo overhand knots significantly weaken the cord they're tied into?

All knots significantly weaken the cord they're tied into. A very significant margin of error is built into the ropes to account for this. Rappel only exerts a force equivalent to your weight, plus a little extra because of bouncing that naturally occurs during descent. 1kN = 224lbs force, so if you weigh 200lbs you can expect to exert about 1kN of force on a static rope. About the weakest static rope people frequent…

> All knots significantly weaken the cord they're tied into. A very significant margin of error is built into the ropes to account for this.

I'm not a climber, what I usually use is cotton, jute, or sisal twine in a day-to-day basis for various tasks. Cotton twine is very easy to keep in your pocket and very clean, but its the weakest by far. Sisal and Jute are scratchy and messy, but they have superior strength.

Lets say you've got a 40lb cotton twine in your pocket. You can either use an overhand knot and drop the strength to ~20lbs, or you can use a figure-eight knot and instead have ~32lbs of strength.

Both the overhand knot and figure eight knot weakened the twine. But overhand knot is among the weakest of knots, with a 50% drop in performance. Having only a 20% drop from figure-eight makes a huge, noticeable difference in strength.

Re: How strong is your knot?

#126

Post by kerkeslager »

dragontamer wrote: post #125
kerkeslager wrote: post #104

Earlier quoted context omitted.

All knots significantly weaken the cord they're tied into. A very significant margin of error is built into the ropes to account for this. Rappel only exerts a force equivalent to your weight, plus a little extra because of bouncing that naturally occurs during descent. 1kN = 224lbs force, so if you weigh 200lbs you can expect to exert about 1kN of force on a static rope. About the weakest static rope people frequent…

> All knots significantly weaken the cord they're tied into. A very significant margin of error is built into the ropes to account for this. I'm not a climber, what I usually use is cotton, jute, or sisal twine in a day-to-day basis for various tasks. Cotton twine is very easy to keep in your pocket and very clean, but its the weakest by far. Sisal and Jute are scratchy and messy, but they have superior strength. Let…

Sure, those might be the numbers in your use cases, with your materials, but I'd be very careful about claiming those numbers if the situation is changed even slightly.

1. Change in strength is dependent on the cord material and weave. Stiffer cord will lose more strength when tied, while more supple cord will maintain its strength better. The tradeoff is that supple cord is more susceptible to tangling. Citing one number as a strength loss for different knots is sure to be false. I would guess, for example, that your cotton twine sees less percentage loss in strength in both knots than your jute.

2. The change in strength is also dependent on the sharpness of the folds in the material. A sharper turn is weaker than a rounder one. If you tie a knot around something, that decreases the sharpness of the turns, which is going to increase the strength of the knots. We aren't typically just tying an overhand or figure 8 midline in a knot and pulling on the ends--I can't think of ANY place where that's useful. The closest thing I can think of is a stopper knot, and neither of these knots is ideal for that application. I'd expect to see a higher loss of strength with flat overhand/flat figure 8, than with a ring bend/flemish bend (which correspond to the overhand and figure 8). This is because the weakest points in the flat knots is the turn entering the knot, whereas the retraced bend versions of these knots, the cord enters the knot in a straight line.

3. Breaking is often not the largest source of failure. A flat figure 8 will roll and come untied long before the cord breaks in most materials, while the flat usually binds within 1-3 rolls. The breaking load of a flat overhand is much, much higher than the rolling load of a flat figure 8 in climbing ropes I've tried it with.

Re: How strong is your knot?

#127

Post by dragontamer »

kerkeslager wrote: post #126
dragontamer wrote: post #125

Earlier quoted context omitted.

> All knots significantly weaken the cord they're tied into. A very significant margin of error is built into the ropes to account for this. I'm not a climber, what I usually use is cotton, jute, or sisal twine in a day-to-day basis for various tasks. Cotton twine is very easy to keep in your pocket and very clean, but its the weakest by far. Sisal and Jute are scratchy and messy, but they have superior strength. Let…

Sure, those might be the numbers in your use cases, with your materials, but I'd be very careful about claiming those numbers if the situation is changed even slightly. 1. Change in strength is dependent on the cord material and weave. Stiffer cord will lose more strength when tied, while more supple cord will maintain its strength better. The tradeoff is that supple cord is more susceptible to tangling. Citing one n…

> We aren't typically just tying an overhand or figure 8 midline in a knot and pulling on the ends--I can't think of ANY place where that's useful. The closest thing I can think of is a stopper knot, and neither of these knots is ideal for that application.

I'll admit that I've mostly used this "useless knot" test methodology you're criticizing here. But in its defense, it is an easy to do micro-benchmark with consistent results.

I guess I could setup a more cohesive test to measure the strength in more "realistic" scenarios. That's really all it comes down to: the strength of the rope in whatever specific situation you're doing.

I'll note that 40lb-strength rated cotton twine is just strong enough to be useful, and just weak enough that a bad knot or two will cause the twine to snap under moderate usage. (Ex: Package Tie to support a box containing 20lb).

Re: How strong is your knot?

#128

Post by WilTimSon »

emmelaich wrote: post #14
dragontamer wrote: post #12

Earlier quoted context omitted.

> I'm somewhat fascinated by people's ability to tie knots that are more complicated than the basic shoelace one. > Even that reef knot gif eludes me -------- These statements are in contradiction. The reef knot IS your shoelace knot. If you can tie your shoelaces, you can tie a reef knot, by definition. Specifically, a "shoelace tie" is the slipped reef knot. "Slipped" means that you leave little loops so that its e…

I think many use the granny for their shoes.

Yup, I do. Never was taught a different method and this one works well enough but I'd really prefer not to spend the rest of my life being so inept at a basic skill.

Re: How strong is your knot?

#129

Post by IgorPartola »

wrycoder wrote: post #113
IgorPartola wrote: post #89

Earlier quoted context omitted.

Depends on the load of course, but in my experience having tied it a lot, it only jammed up once, taking an extra thirty seconds to undo. This was when I put about 200 lb on it and swung around a bunch. Jute rope also has a ton of friction, synthetic being smoother would be even less likely to jam.

It's an interesting and decorative knot - I've not seen anything like it before. I'll have to give it a try. I'm trying to think of another quality bight knot that can be tied with the object in place. Not the bowline, not the butterfly.

If you want another one, check out the WykD Fast Bowline. It can be tied as both a regular version and a quick release. It is even simpler but has less symmetry. Interestingly, the quick release is more structurally sound with this one. There is also a variant of the Somerville where the loop is made backwards, which seems to go by Struggler’s knot. It purports to be nearly as strong, and supposedly can be tied with one hand.

Also, there is a method of tying the Somerville called the reverse Somerville. It’s the same knot but tied inline rather than with the bight.

The downside to the Somerville is that you generally can’t get it really tight around the object. A variant of it exists which allows you to do so at the cost of a bulkier knot: before making the loop, cross the bight over all the rope, go under it and come back to where it just was, similar to how you would start a reef knot. I have used that technique before with some success but not enough to recommend it beyond messing around.

Re: How strong is your knot?

#130

Post by Balgair »

wenc wrote: post #116
Balgair wrote: post #111

Earlier quoted context omitted.

Knots aren't super difficult to 'program' in the first place. The first computers were for looms and their weft patterns, after all. It's always been strange to me that no one has decided to set up the math of knots. Most knots are just subtle changes to the same basic elements (bite, over/under, loops, etc). I'd figured there are enough Eagle scouts with PhDs in math to have done this already, but no.

Knot theory https://en.wikipedia.org/wiki/Knot_theory

I meant more like how to actually tie a knot, not just topologies.
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