11/17/2016 10:53 PM
The offset bound overhand bend is utilized to join ropes together. It is a variant of the EDK or simple overhand, by adding an additional choking turn, which enhances the stability of the knot. What is normally critiqued concerning the EDK is the potential for the knot to capsize (roll). It is because of this potential for rolling that it is recommended that the tails are at least 12”-13” in length. We have used the EDK quite a bit, mainly with one-person loads, but occasionally with two-person loads, and have never had it roll once. The instances often quoted of EDK failures that resulted in death (4 total), have been shown to be a flat figure 8 in at least 3 of those cases. Anyway, research for yourselves, look at the amount of kN’s that it requires for the knot to roll and examine whether you would ever place that much force on your specific system (usually just a one-person descent). When examining the pull tests, also note what kind of rope is being used, dynamic vs. static.
Okay, back to the offset bound overhand bend… it adds another choking turn that helps resist capsizing, increasing the stability. We have added a couple published tests for your review, one involves dynamic rope and the other static lines. Look at the kN’s for rolling and breaking…and remember 1 kN = 224.8 lbf.
Why we dig it… It’s fast, strong & secure for its intended use, and easy to untie after loading.
As discussed in the video, there are a bunch of different “offset” knots. Offset refers to the way the knot / nub is non-linearly loaded when force is applied. When this knot is loaded, the nub is to the side of the axis of force, the benefit is that the knot tends to turn inward to present the flat side of the bend to the rock edge. This reduces the potential for stuck lines when retrieving or lowering a casualty. We also mention that offsetting the tails assists in the manipulation of the rope around a DCD without having to “pass a knot” when using lower diameter ropes (video coming soon).
Last comment, whether using the EDK or the Offset Bound Overhand Bend, dress and manually pretension (set) your knot before loading. Most recommend having the tails at least 200mm or ~8 inches.
Element Rescue, Knot Series 11/17/2016