I use 15mm webbing for handlines, and occasional “easy terrain” rappels. There are times when I have to join two pieces of webbing through a small quicklink, and it is often easier to tie a flat overhand (the dreaded EDK) to join two strands rather than tie a water knot/ ring bend.

But the ACA advises against using an EDK for webbing, via Rich Carlson, who does give some exceptions (and who urges people to think elsewhere). I found the trouble is getting people to think.

So I did an experiment, with 15mm nylon webbing, to mimic one of Rich Carlson’s tests with 9mm rope and a 6 mm pull cord.
Here are two screen shots from Rich Carlson’s video to show the setup we are trying to mimic, and how it broke. Note that both our setups put all the force on one side – in his case, on the 9 mm rope with a reported breaking strength of 5139 lbs, which broke where it bent over the quicklink for a max force of 2354 lbs (2082 at breaking), for 46% of the rope strength. Rich used a comealong to supply force (as did I); since his intent was to load only the 9mm rope (using the EDK as a knot block), he put the load cell on the other side of the quicklink.



Below is a schematic of my setup, followed by a figure to show the real setup after the webbing broke.



I was not sure the EDK would keep all the load on one side for the entire experiment, so in my experiment, the “load cell” (crane scale), and the source of force, was placed on the leg “opposite” the EDK, and the other strand of the webbing was fixed to a tree. The webbing was attached to the anchors by wrapping it 5 times around a ¾” shackle or hook and tying off the ends with a few half-hitches—effectively this is a capstan clamp for each strand on the west side anchors (the shackle was in the end of a tree-saver strap, the other wrap was on the power-puller hook).

The webbing broke just inside the knot, at the exit from the EDK, at 1236 lbs. The strength of the webbings is given variously as 2023 to 2300* lbs; using the latter, the webbing broke at 54% of the native strength, so “better” results than Rich obtained. But the effective diameter of 15mm webbing over a quicklink is only 2mm, so the 9mm rope saw much more stress at its sharp bend..

And now for the magic of geometry and forces. When I rap down two strands tied in an EDK above the quicklink, I put half of my weight on each strand— my EDK isn’t intended to act as a knot block; so the “strength” of the 15mm webbing setup can be as high as 2472= 2x1236 lbs, relative to my weight.

* Note ”15 mm” webbing varies quite a bit in mass/length; this particular webbing is actually 16 mm wide. Over the years REI has labelled the thin Bluewater webbing variously as 15mm, 9/16”, and 5/8” (the last is ~16mm).