That doesn't matter. The system is only as strong as it's weakest link. In a balanced system, one side can be infinitely strong and have no bearing on the system strength. That doesn't change the strength of the other side and once it fails we're in trouble.
In your example, a single line is reduced to about half its strength. But in a doubled system as pictured:
Yes and no, since the load is spread between the strands the force the weak link would see would only be half hence the loop is usually 1.5 times stronger than the individual strand. And that’s with a 50% loss at the knot, as you know some knots do not cause a 50% reduction either. Still a good safe precautionary figure that you use.
That’s correct sir. The magic number for a full body arrest harness is under 1800 lbs because any forces over that would be catastrophic for the human body to absorb. I have used those same calculators, but ideally we will never be above your connection points to have a true long distance fall. The forces can indeed be scary.
With all due respect, my example is correct. A 50% efficient knot on a loop gets ya back to 1x the MBS of the cord, not 1.5. The strength of the strong side does not play into the calculations at all. Only the weakest link does. And when that bend in my picture sees 500lbs it goes and at that time, the other side is also seeing 500lb. It could see 1000, but it never will because it's a balanced system. To calculate total strength, We don't add the cumulative strength of the Strands. We double the weakest one.
A Distel used with a single eye is the Tautline Hitch, just as the Michoacán is a double eye Blake’s.
In your excellent example, which is basically the same as my picture, a continuous loop provides a 2000lb strength. The loop with a knot on one side breaks at 1000lb. If ya put a knot on both sides, still breaks at 1000. If ya make that loop out of 20 little pieces of cord, all knotted together, it still breaks at 1000. Is a balance system, with the beaners acting effectively as pulleys. There will never be more load on one side than the other.Y'all either need to stop mathing or pass out some ibuprofen.
Let me throw this out and yall decide if my example is correct. If we clip a rubber band, only thing I could think of with no knot or splice, between the carabiners like in John's pic and the strand of the rubber band has 1000 break strength, it has 2000 lbs of break strength when connected to the carabiners. If we then cut one side of the loop and tie a hunters bend for example, we would have effectively reduced the strength to 1500 due to the bend on one side of the loop system. Yay or nay?
I see both arguments here. John's argument makes the most since to me because the integrity of the loop system is going to be determined by the strength and load capacity of the bend and nothing else. I also do not disgree with the math looking at it from the other angle.
With all due respect John literally every rope manufacturer disagrees with you, as does the results of numerous break strength tests. Since the weakest point only sees 50% of the load, the break strength of a loop, will be equivalent to 1.25 to 1.5 times the single cords breaking strength. Again I like your math for a conservative safety factor but it isn’t
ok so if the original strength was 1000 then the loop is 1.5 times stronger because 1000 times 1.5 is 1500 that’s the math.Y'all either need to stop mathing or pass out some ibuprofen.
Let me throw this out and yall decide if my example is correct. If we clip a rubber band, only thing I could think of with no knot or splice, between the carabiners like in John's pic and the strand of the rubber band has 1000 break strength, it has 2000 lbs of break strength when connected to the carabiners. If we then cut one side of the loop and tie a hunters bend for example, we would have effectively reduced the strength to 1500 due to the bend on one side of the loop system. Yay or nay?
I see both arguments here. John's argument makes the most since to me because the integrity of the loop system is going to be determined by the strength and load capacity of the bend and nothing else. I also do not disgree with the math looking at it from the other angle.
I'm only an engineering school drop out and I wont argue with studies saying otherwise, but this example is wrong to me and I'll die on that hill. regardless of knot efficiency or cordage rating, this example shows a single strand being loaded on a point the size of your carabiner's cross section, which is to say not very big. To me there is no difference between this loop and a single piece of this cordage, if you doubled you loop so that there were four strands between the carabineers and two strands across the carabineer cross section you could claim increased strength, but clipping into a loop like in this picture wont give you any more strength than having a single strand of this cordage and loop on each end of it.In your example, a single line is reduced to about half its strength. But in a doubled system as pictured:
1. Assume this 4mm cord breaks at 1000 lbs.
2. Assume the hunters bend is 50% efficient.
3. It will break at 500 lbs when tied with 1000lb cord.
4. At the time it breaks in this balanced system, the system would have been holding 1000 lbs.
The strength of the strong side never plays in. Figure out where the knot breaks, then calculate the system load at that time. This is a simple example but relevant given that this is the general construction of my friction hitches. And an obvious advantage to using an eye to eye, where appropriate or possible. That's why arbs on a hitch climber pulley DRT system have a more robust system than those with a Poachers (double fish) on the ends. But in the real world, because we are overdesigning our systems, we're never going to know where they break... Unless we do load testing, and so its good to know the theory.
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I understand what he means that the knot is the same break strength regardless but because there are now two legs, the knot is not seeing the same force, it only sees half which means the loop will be around 1.5 times stronger than the original MBS. Saying anything else causes confusion and makes people think their prusik loops are the same strength as the regular cord. All myself and Brocky were saying is that is not the case due to the rope now being in loop configuration. So a 1000 lbs single cord tied in loop will not break at 1000 lbs, it will break around 1500.
Just got out of a meeting and havent watched the video but did the ropes consistently break at the bend or knot?
