11/9/2016 2:25 AM
The Water Knot is the traditional knot used to join the ends of webbing, but as stated in the video, “can take an act of God to untie”. Untying is a big deal. Why? You may not always want your webbing tied in a loop. You may need to join multiple lengths of webbing and use to bail-out, lower a casualty, assist with edge transition, or perform a nuisance rappel. Also, there was a great study of the water knot by Tom Moyer presented at the 1999 ITRS conference. Basically it stated we really do not have to worry about a single dynamic failure of the water knot, but rather be concerned with a cyclic failure. With a 250-pound load, the tails of the water knot slipped 0.0035 inches per cycle... so with the typical 3” tail, the magic number was 806 cycles before one of the tails (Top) slipped through. Interesting to note, it was cycles...not creeping.
Tom’s conclusions were as follows; “Water knots definitely fail by slipping under cyclic loading. Low loads, such as body weight, are sufficient to cause failure. Other knots (such as a single fisherman's) tied in the same material do not exhibit this kind of failure. Overhand safeties tied on top of a water knot may prevent the failure, but do not guarantee it. This is not all bad news for water knots. I now understand the mechanism of failure and know how to prevent it. This is a lot more comforting than using a knot about which I have suspicions. I will always check the length of the tails on every water knot - and particularly every fixed rappel anchor tied with a water knot - before trusting my life to it. We will continue to use water knots in Salt Lake County, and continue to require long tails on this knot as we always have.”
Element Rescue, Knot Series (09/06/2015)