In the summer of 2006 I was allowed to use the materials testing lab at Purdue University's School of Materials Engineering to test the strength of a variety of knots. I just dug up my data and discovered that I didn't test the bowline. Here's the list:
* Unknotted Line (as a control)
* Zeppelin Bend
* Double Figure 8 Bend
* Johnson Hitch
* Full Nelson Loop
* Full Nelson Bend
* Full Nelson Bend Simple
* Fixed Noose
The FN Loop was probably version 1. One of the 2 FN Bends was the basic FN Bend that I have on my site, the other would have been either the same with an extra wrap, or the same with one less wrap. I took before and after photos of all the samples, and if I can find them I may be able to tell which it was. The easy-releasing elaboration of the FN Bend that I just discovered was not included.
The Fixed Noose was another knot I came up with. It looks like like a hangman's noose, but doesn't slide. I'd hoped that all the turns would make it stronger, but it turned out to be one of the weakest of the bunch. So it goes.
The tests were performed on a big, expensive, computer-controlled machine whose name I can't recall (MTS 810 servohydraulic system?). It had two large hydraulic rams that lifted a heavy cross-bar. The test samples were attached to grippers on the machine's base and cross-bar, and the test program slowly extended the rams, taking measuremnts of the strain through a load cell, and continuing until the sample broke.
I tested at least 3 samples of each knot (and the unknotted line), using some utility cord (10mm?) purchased from a local sporting goods store.
Note that the highest strain wasn't necessarily the last line of data. The strain would generally drop off a bit near the end, when a lot of the strands had broken and the last few were stretching toward failure and unable to provide much resistance. As the samples approached their failure point they'd typically show at least 2 or 3 sudden drops in the strain as fibers in the core snapped. The strain would usually go through a few peaks of increasing height, followed by drops, before finally failing completely.
The unknotted line failed between 570 and 580 lbf., and was, of course, the best result from all the tests. The Zeppelin Bend made it to 365-371 lbf., and the Double Figure 8 reached 362-385 lbf.
The FN Loop highest strains were 408-428 lbf., which really surprised me. I'd expected the Double Figure 8 to be quite a bit better than anything else, but the FN Loop exceeded it by a significant margin.
The FN Bend rated 354-401 lbf., and the simple version ranged from 349-407 lbf. I have 4 samples for the simple FN Bend, and the lowest test is significantly lower than the other 3. I believe that's because that was the test where one of the grippers failed.
The Johnson Hitch only reached 314-365 lbf., and my Fixed Noose ranged from 319 to 380 lbf.
I really wish I'd had time to test a bowline or other common loop knot. (I had my kids with me, and after a few hours they started getting cranky.) The FN Loop looks good compared to the bends, but maybe loops in general fail at higher strains than bends. In that case, the FN Loop might turn out to be at the low end of loop strength. (The relatively weak Fixed Noose would argue against that interpretation, however.)
At the moment I can't say, but I can say that it was stronger than a Double Figure 8, which I've always heard was considered to be very strong.
I've made all the data from those tests available as a .zip file, and it's free for anyone to review and share as long as the accompanying ReadMe.txt file is included. I just added a link to it from my knot page, and someday I hope find time to graph all the results and include photos of the samples. Here's the location:
http://hilarynelson.com/Hobbies/Knots/KnotLoadTests.zipAs for slipping a Lapp bend... I can't say because I'm not familiar with it. I tried to find something about it on the web, but all I could locate were text descriptions, which I couldn't quite follow. Can you point me to any place where I can see a diagram or photo of one?
Thanks!
-Hilary