5 ms·

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 s

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.

dragontamer 7y ago
> 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).
- kerkeslager 7y ago
  > 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. That's fair, and it does prove that different knots affect strength differently. That's a base principle that is useful to know even if it doesn't get you far on its own. With regards to your application: while it lacks the "finesse" of tying knots that give you just enough strength, simply getting stronger twine would solve this problem without the complexity. In general, there's a whole lot of ways knots can fail. If you can solve the problem by just using stronger cord, that frees up mental cycles for dressing, avoiding slippage, effective communication, ease of untying, etc. If you're just tying up boxes do whatever you feel like doing. But for climbing, I'd rather have the rope be more than strong enough to do its job, and have those brain cycles for focusing on preventing other system failures.
  - KirinDave 7y ago
    For what it's worth: lots of knot literature and lore cautions people about overhand knots as weaking the line more than other knots. That's why I asked.

dragontamer 7y ago

> 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).

kerkeslager 7y ago
> 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. That's fair, and it does prove that different knots affect strength differently. That's a base principle that is useful to know even if it doesn't get you far on its own. With regards to your application: while it lacks the "finesse" of tying knots that give you just enough strength, simply getting stronger twine would solve this problem without the complexity. In general, there's a whole lot of ways knots can fail. If you can solve the problem by just using stronger cord, that frees up mental cycles for dressing, avoiding slippage, effective communication, ease of untying, etc. If you're just tying up boxes do whatever you feel like doing. But for climbing, I'd rather have the rope be more than strong enough to do its job, and have those brain cycles for focusing on preventing other system failures.
- KirinDave 7y ago
  For what it's worth: lots of knot literature and lore cautions people about overhand knots as weaking the line more than other knots. That's why I asked.