Note - This post discusses techniques and methods used in vertical rope work. If you do them wrong, you could die. Always practice vertical rope techniques under the supervision of an experienced climber, and ideally in a progression: from flat ground, to staircase, to vertical close to the ground before you ever try them in a real climbing situation.
Scenario: You’re the last one rapping on two ropes tied together and you’re worried about the knot sticking on the corner of the ledge or in a crack near the anchor. (In the Portland Oregon area, the rappel off of Rooster Rock in the Columbia River Gorge has a notorious knot-eating crack at the top, and is a great place to use this technique.)
Try this Crafty Rope Trick (CRT) to move the knot past the obstacle.
Move the knot as close as you can to the ledge, obstacle or crack you’re concerned about.
Girth hitch a two foot single runner above the knot, clip the other end to your belay loop with an extra carabiner (not the big locker to which your rap device is attached), and begin to rappel.
The knot will move along with you as you rap down. Once the knot is past any ledges or cracks where it might hang up, unweight the rope for a moment, unclip the runner from your harness, remove it from the rope, and continue your rap to the bottom.
This may be a little hard to visualize when you first read it, but try it once or twice and it should make sense.
A few cautions:
1) Practice this in a safe place! A staircase is a fine place to learn. It’s a little unnerving to see one side of the rope NOT sliding through your rap device, and the other strand sliding through twice as fast!
2) Note that doing this will cause one end of the rope to rise, so be sure both ends of the rope touch the ground or reach the next rap station with room to spare. Follow the best practice of always having a stopper knot in the end of your rappel rope. The first person down has the task of managing the rope ends. On a multi pitch rappel, a good way to do this is threading one rope end through the lower anchor and then tying the ends together to be sure the rope strands stay connected to the lower anchor.
3) This trick is more complex on a free hanging rappel, as this make unweighting the rope a harder maneuver. If you see that the first few feet of your rappel is completely free hanging, then you want to add a load releasable hitch, such as a Mariner’s knot, or maybe a Purcell prusik (which can extend under load) to the system so you can release it under tension.
4) Be sure and use a single length / 60 cm runner. Using a longer runner may cause the knot to be out of reach when you want to remove it from the rope.
5) Only do this when you have a metal-to-rope (carabiner, rap ring, chain, or quicklink) connection at your anchor. This technique causes the rope to slide through the anchor under load. This is something you NEVER want to do with a webbing connection, even if it's only for a few feet.
6) Hopefully this is obvious, but this maneuver only needs to be done by the LAST person coming down the rope.
1 - Rig for normal double rope rappel.
2 - Girth hitch a single length / 60 cm runner above the knot connecting the ropes.
3 - Clip the runner to your belay loop. (Note: in the photo below it’s clipped to the belay carabiner; the belay loop is better.)
Now as you rappel, the knot will move along with you. When the knot is past the obstacle, unclip the runner from your harness, remove the girth hitch, and continue your rappel.