The following article is courtesy of Kolin Powick (Rock and Ice Magazine)
There are advantages and disadvantages to each type of rap knot, but is there one that is superior in strength to the others? I put all three knots (with three different rope diameter scenarios) through a quick-and-dirty series of pull tests and have provided below some basic strength testing data based on my limited testing of the three most common rappel knots. (Note: only two data points per configuration.)
- The Double Fisherman’s and Ring Bend had similar strength results
- The Euro Death Knot was the weakest: ~20-30% less than the Double Fisherman’s and Ring Bend.
- The Euro Death Knot slipped a bit before failure at ~4000 lbf with the 10.2 and ~2000 lbf with the 8.1 in the system.
The reality is that all three of the methods for joining two ropes for rappelling that I tested were PLENTY strong for the forces seen during a typical rappel (i.e., bodyweight-plus, taking into account some shock loading when bouncing around, jiggering with tangled lines, not smooth rappelling technique, etc).
For what it’s worth, when I started climbing I always used the Double Fisherman’s, but now I’ve fully converted to the Euro Death Knot—it’s fast to tie, plenty strong, less likely to get hung up when pulling and easy to untie. And finally, no matter what rap knot I tie, I always leave long tails (like at least 12 inches).