Traveling double rope
Often useful only for LAMAR, this technique involves rappeling double rope occasionally locking one of the strands and leaving the other move.
The construction is essentially the same as a double strand rappel (toss and go). However, the rappel is controlled with both hands, one hand to control each strand independently.
Every few seconds one of the hands grips tightly while the other lets go smoothly. This will cause one strands of rope to move down with the rappeler and the other to move up, changing the abrasion point in the process.
This system is useful to move the abrasion point and protect the rope.
It may also be very useful to facilitate the pull in difficult rappels where ropes tend to get stuck. The last man down can have the block/knot travel along with him until it gets over the edge and out of risk of getting stuck, then rappel double strand as usual.
It requires using both hands, which can be both difficult and risky in some circumstances.
- Alternately, girth hitch a runner between the knot and the anchor and clip the other end into your harness belay loop. As you rappel, the ropes will slip and bring the knot with you. As soon as you are clear of the edge, unclip the runner from your harness. Con: the runner will come down during rope retrieval, but increases the odds of it getting caught on any obstructions on the way down.
This technique should NEVER be used when landing in a swift water pool because of the danger of rope entanglement.
Because it requires using both hands, great care should be taken to not let go of the rope with ANY of the hands.
Make sure to dress the descender accordingly for which strand of the rope you want to run. For most Figure 8 shaped devices, only the front rope at the 8 bend will be able to run, the other strand (the one that lies behind) will not.
In some circumstances, shifting the rope via this technique may result in a rope that no longer reaches the ground.