We all know friction in a mechanical advantage block and tackle pulley systems can reduce output, but I haven't heard anyone talk about stretch. I am always using semi static or climbing ropes, which have a lot of stretch. We test all the way up to a 13:1 with dynamic, semi static and 0 stretch dyneema. We did NOT use multipliers or brakes to simplify this already long experiment.
*All numbers are in kN. Trying to keep a lot of data easy to look at!

This unlisted video of our 81:1 (that doesn't work) inspired our "9:1 is not 900%" video    • 81 to 1 pulleys for break tests in re...  

►►►DYNAMIC ROPE
►1:1 pulleys n/a - 1.34 INPUT x 1.19 OUTPUT / 100% vs Actual 88%
►3:1 with pulleys - 1.13 INPUT x 2.26 OUTPUT / 300% vs Actual 200%
►3:1 without pulleys - 1.19 INPUT x 1.99 OUTPUT / 300% vs Actual 167%
►5:1 with pulleys - 0.89 INPUT x 3.84 OUTPUT / 500% vs Actual 431%
►5:1 without pulleys - 1.39 INPUT x 2.38 OUTPUT / 500% vs Actual 171%
►9:1 with pulleys - 0.85 INPUT x 5.92 OUTPUT / 900% vs Actual 696%
►9:1 without pulleys - 1.12 INPUT x 2.38 OUTPUT / 900% vs Actual 212%
►13:1 with pulleys - 1.01 INPUT x 5.04 OUTPUT / 1300% vs Actual 499%
►►►SEMI-STATIC ROPE
►1:1 pulleys n/a - 1.62 INPUT x 1.26 OUTPUT / 100% vs Actual 78%
►3:1 with pulleys - 1.31 INPUT x 3.46 OUTPUT / 300% vs Actual 264%
►3:1 without pulleys - 1.72 INPUT x 2.48 OUTPUT / 300% vs Actual 144%
►5:1 with pulleys - 1.10 INPUT x 5.15 OUTPUT / 500% vs Actual 468%
►5:1 without pulleys - 1.18 INPUT x 2.67 OUTPUT / 500% vs Actual 226%
►9:1 with pulleys - 1.31 INPUT x 7.48 OUTPUT / 900% vs Actual 696%
►13:1 with pulleys - 1.4 INPUT x 6.98 OUTPUT / 1300% vs Actual 498%
►►►DYNEEMA ROPE
►1:1 pulleys n/a - 2.33 INPUT x 2.07 OUTPUT / 100% vs Actual 89%
►3:1 with pulleys - 1.34 INPUT x 4.04 OUTPUT / 300% vs Actual 301%
►3:1 without pulleys - 1.47 INPUT x 2.97 OUTPUT / 300% vs Actual 202%
►5:1 with pulleys - 1.67 INPUT x 6.71 OUTPUT / 500% vs Actual 402%
►9:1 with pulleys - 1.47 INPUT x 9.62 OUTPUT / 900% vs Actual 654%
►13:1 with pulleys - 1.51 INPUT x 8.54 OUTPUT / 1300% vs Actual 565%
►►►THOUGHTS:
*** % wasn't that different but my input is so much greater not fighting stretch
***9:1 is better than a 13:1 and might be worth using, but a 5:1 is the most optimal to get as close to theoretical as possible

This is a very helpful article https://overtheedgerescue.com/pulley-...

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Its a Myth!
01:34 Dynamic Rope
5:04 Semi Static Rope
06:53 Dyneema
09:45 Applying the science!
12:01 Conclusion