Avoiding snags when pulling a rappel rope
When rappelling, you always have a choice as to which side of the rope to pull. While on many routes it doesn’t matter, on some raps it may be the difference between having a stuck rope and/or a very difficult pull. Look carefully at every rappel you do, and try and identify potential problem points before pull the rope.
Generally, try to pull the rope AWAY from any obstacles it may hang up on. For example, say you’re about to pull a single rope rappel, and you look up and notice a potential rope-eating shrub, block or crack below and slightly to the right of the anchor above you. Pulling on the left strand of the rope will cause the rope to fall to the left a bit, hopefully away from the potential hang-up point.
If you’re doing a double rope rappel, you need to anticipate problems BEFORE you rig your rope. Get into the habit of looking down at the cliff below you before you thread the rope. Do you see a shrub or rope eating crack to the left? To keep your rope away from that, you probably want the knot on the side on the anchor away from that obstacle (or, to the right as you’re looking down.)
Look up at the rope as you're pulling it. If the rope gets hung up on something, you might be able to see how it got hung up, which could help you solve the problem.
If you’re on the ground when you pull the rope, you’ll almost always get a better angle of pull if you walk as far away from the wall as possible. If there's a snag point, say on the left as you're looking up, step away from the wall and to the right as far as you can. This can decrease risk from falling rock, and minimize friction.
image: From the book “down”, by Andy Kirkpatrick. Used with permission. andy-kirkpatrick.com
On steep terrain, give the rope an extra flip or sharp tug just AFTER (not before) it slides through the anchor. This can cause it to fall farther away from the rock, further avoiding snags. Avoid the common mistake of giving a tug on the rope BEFORE it goes through the anchors. Doing this can cause the free end to whip around the other strand and make some random evil friction hitch that can block your rope. (I know this from painful experience . . .)
But on lower angle blocky terrain, (or in high winds), it might be better not to do this and just let the rope slither down the rock under its own weight.
If the anchor below you is off to one side, say the right, you should set your rope so the pull is in that direction. If you don't, the ropes can cross at the anchor and create a lot of extra friction.
image: From the book “down”, by Andy Kirkpatrick. Used with permission. andy-kirkpatrick.com
If the wind is coming strongly from a certain direction, rig your rope to pull it into the wind. Or, in other words, if the wind is coming from the left, pull the left strand. Doing this makes the tail blow away from the pull strand, which reduces friction and hopefully avoids wind-induced rope mayhem.
If you’re rapping in terrain where rope snag potential seem to be everywhere, you're probably better off doing a series of shorter raps using a partial length of the rope. It can be a better choice to have more rappels, but less chance of getting your rope stuck.
Maintain control of the “up” strand until the last possible moment. This can be especially important on overhanging, traversing, or windy situations. If you get lazy with this, it's all too easy to have a stopper knot still in the end of the rope, you losing control of it, and having it swing out of reach. Big problem.
In terrain with high snag potential, another option is lowering the first person and having the other end of the rope tied to them. This of course does not help with pulling the rope, but it can get it down more efficiently.
If you’re doing short rappels in terrain with a lot of rope snag potential, try this: If you have plenty of rope at the lower anchor, pull down as much rope as you can before the final person goes on rappel. This reduces the chances for a hangup or rockfall when the rope is pulled and before it goes through the anchor, because less rope overall is moving through cracks, over blocks, around shrubs, etc.