Rope blocks 101
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 a qualified instructor, 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.
This article was written with collaboration from Ben Wu, AMGA Certified Rock Guide. Connect with Ben at www.benwu.photography.
Rope block. Knot block. Carabiner block. Static block. Reepschnur.
They all mean pretty much the same thing: creating an obstruction on one strand of your rappel rope, that cannot be pulled through the anchor master point.
The rope can slide freely in ONE direction, but not in the other.
Doing this lets you rappel a single strand on the “fixed” strand of rope.
Main climbing application: it allows a retrievable single rope rappel; you carry less rope and weight.
To retrieve your rope, typically you use a lighter line such as a 6 mm pull cord (like the Petzl PURline) on the free running strand of rope.
Like everything in climbing, there are some definite pros and cons to this technique. If you’re considering using it, it's good to be aware of all of them. So let's get into it!
Conceptually, it's pretty simple. In practice:
There are some subtleties to doing it correctly.
There are some downsides to it even when you do it correctly.
If you screw it up, you could die or get your rope hopelessly stuck.
For these reasons, I personally consider it an advanced technique that you absolutely should practice with a qualified instructor. And, even when you’re confident with it, I feel it should generally not be part of your regular practice. It can definitely get you out of a jam in certain situations, but there are enough moving parts that I feel it's not a routine technique for most recreational climbing situations.
Here are articles on two closely related techniques that use rope blocks:
Not to dwell on the potential problems, but here are two reports of fatal accidents from rope blocks gone wrong:
First off, let's be clear on the Golden Rule of a rope block: it absolutely, positively cannot pull through the rappel hardware.
If you have not closed the system by attaching the pull side of the rope to the rappel side of the rope and the block pulls through the hardware, you will probably die.
If you have closed the system and the rope pulls through, your rope will probably be hopelessly stuck.
Take a close look at the anchor hardware and the diameter of your rope. If there is the slightest chance that you think the blocking knot could pull through the anchor hardware, then don’t use a knot block! (Consider a carabiner block instead, more on that below.)
There are really only a few times in recreational climbing when you might want to use a rope block.
You’re using a pull cord to do full length rappels. In this case, a rope block is pretty much mandatory. (Yes, there are some advanced ninja rope tricks like using a Stone hitch and a Fiddlestick to use a pull cord a different way, but we're not gonna get into that here.)
Your rope is too short to make the rappel. Lower your partner to the next station, make a rope block, and then extend” the “pull” side of the rope with whatever extra cordelette, slings, etc. until your DIY extension reaches the next anchor station.
There are two other situations where people often think they need a rope block, but there are other techniques you can use instead.
You damaged your rope and need to rappel. You rappel on the good half of the rope and use the damaged half of the rope with a knot block as a pull cord. To avoid doing this, you can do a counterbalanced rappel, read about it here.
If both partners have a Grigri, and you both need to rappel. It's pretty unlikely that both partners will have Grigris and not a tube device, but I suppose it could happen. You could use the counterbalanced rappel technique described just above. If one person has a Grigri and the other person has a tube style device, there are lots of other options for getting both people down without using a knot block, see some of them here and a photo example below.
Potential problems of a rope block (and pull cords)
The big one was already mentioned, but it's worth saying again: if the knot pulls through the hardware, the entire system fails and you die, or your rope gets stuck.
You’re adding an extra knot and carabiner to your system, which are two more things that can potentially get snagged when you're pulling your rope.
There are increased steps and complexity, which can increase the chances of making a mistake. This is especially true because for most people, this is a non-standard system that doesn’t get used regularly. See accident reports at the top of the page.
If you're using a lighter weight pull cord, if you pull your rope and it gets snagged after the end of the climbing rope is out of reach, you only have a pull cord in your hands to deal with the problem. Not good.
Maybe you forget what side to pull, whoops. It can be good practice to establish which side you block and which side you lower off of and do this pretty much all the time. For example. “L”=Left=Lower, and “R”=Right=Retrieve.
If you're doing multiple rappels, you can’t do the standard trick of feeding the pull strand through the bottom anchor and then pulling the rope. Why? Because you’re pulling the skinny cord, but the thick rope needs to be the one through the anchor. This means you have to re-rig the entire system at each rappel station, which takes additional time.
Yarding on a 6 mm rope can be rough on your hands. Consider adding a Tibloc or Micro Traxion on the pull cord to make the pulling easier. Gloves are recommended.
Pulling the rope can be significantly harder, because you do not have a counterbalanced weight on the pulling strand to assist your pull.
You’re rapping on a single strand of rope, which might be uncomfortably fast. Be sure you know some ways to add friction to your rappel.
If you keep the safety carabiner clipped when you pull, it can add a significant amount of extra friction, making your rope pull more difficult. This can be especially true on a low angle slab.
If you keep the safety carabiner clipped when you pull, sometimes the ropes can more easily twist together, which can cause your ropes to get stuck.
If you keep the safety carabiner clipped when you pull, you've essentially created a closed loop that you then need to pull down. If the two sides of the rope making this loop happen to go on either side of some rock spike, boulder, shrub, ice blob, etc., the loop is going to get caught when you pull down your rope, causing your rope to get stuck. This is probably difficult to visualize, so check out the photo below. (Yes, it’s a flower pot, but I think you get the idea . . . =^)
Rope block backups, pros and cons
It's good practice to backup a rope block by clipping the blocking knot onto the rappel strand with a locking carabiner. In the unlikely event of the block pulling through the hardware, this will save your life.
The backup stays in place for everyone except maybe the last person.
If the block is closely inspected after being fully loaded, and you are 150% sure that it cannot pull through the hardware, then the last person has the option of removing it. In many cases, this is a good idea.
Removing the block for the last person eliminates several of the problems mentioned above.
This is a call that the last person gets to make. (Like most everything in climbing, this is a subjective choice, and not a black and white rule.)
What’s the best anchor hardware for a rope block?
Small-medium size quick links, chains or small rappel rings are the most secure hardware for knot blocks. The openings are small and it's pretty much impossible for a blocking knot to be pulled through them.
Lots of people like to hate on carrying quick links, but this can be an outstanding time to use one. Keep in mind that a 5 mm, stainless steel, CE approved, 25 kN rated quicklink from CAMP costs about $6 and weighs just 22 grams. So weight, cost, and strength are not issues with carrying quick links, provided you get the right ones.
Some not-so-great hardware for a knot block would be a carabiner or Mussy hook. These have larger openings and greatly increase the chance of the knot pulling through. Remember, the knot will shrink as it’s loaded.
Nice diagram from the superb Petzl website. Small quicklink on the left, probably good. Large ring on the right, bad, the knot could pull through.
image: https://www.petzl.com/US/en/Sport/Multi-pitch-rappelling-with-a-single-rope?ProductName=PUR-LINE-6-mm
What about a carabiner block?
Another option is to put a clove hitch onto a large HMS locking carabiner to serve as a block. This can work if the anchor hardware is something larger, like carabiners or maybe a Mussy hook. This is definitely an advanced technique that I recommend practicing with a qualified instructor.
Take extra attention to tie the clove hitch properly and dress it well. Test it when you're done by holding the carabiner with one hand and pulling hard on each strand of rope with the other. If the rope moves, you might have tied a Munter instead, and that is a Big Problem (photo below). If your rope is larger diameter (10+mm) or has an old crusty sheath, the clove hitch may not hold very well. This technique works best with newer ropes that are of standard climbing diameter around 9-ish mm.
A carabiner block looks something like this. Note that the block is backed up by a bight knot clipped with a locker onto the anchor, with a bit of slack in it. The slack shows that the carabiner block is properly behaving. The last person can remove the blue carabiner and untie the bight knot. Or, if they are feeling extra cautious, they could clip the blue carabiner onto the left strand of rope as a back up. Again, this adds more hardware that can get hung up when you pull your rope, so it's a trade-off.
Is it OK to load a carabiner like this? Yes, it’s fine. You are not putting any two or three way loading on the carabiner. It’s holding body weight only, and there's no way the carabiner will be damaged rigged like this.
With a carabiner block, be SURE you tie a clove hitch and not a Munter hitch!
What knot should I use for the block?
An overhand on a bight, figure 8 on a bight or a butterfly can all work as a knot block. In these examples I’m using a butterfly. Be aware that all knots will tighten under load and become smaller. Remember the Golden Rule: if you think there’s the slightest chance of the knot pulling through the hardware, then don't do it!
A flat overhand bend (formally known as the “EDK”) can work, depending on the diameter of your rope, and if you're using small anchor hardware, like chain links.
An overhand on a bight is slightly smaller profile than the figurine or butterfly. This could be a good thing as it's less likely to snag one pulling down your rope, or it could be not so great if there's a slight chance of getting pulled into your hardware. Pros and cons to everything . . .
Will the blocking carabiner get damaged when I pull the rope?
Probably not.
Some people seem to be concerned that the carabiner clipped to the blocking knot is somehow going to fall and maybe be damaged when you pull the rope. Why does this not happen?
With any rappel much less than the full length of the rope, the carabiner will be pulled to the lower anchor and be in your hand before the other half of the rope even starts to fall down.
However, it may bounce around a bit on the rock and get dinged up on the way down. If this concerns you, you can use an older carabiner or a steel quick link. Or, if you have complete confidence in the knot and the anchor hardware, you can remove the backup carabiner for the last person.
What about rapping with a Grigri, don't I have to use a block to do that?
Nope. There are lots of different ways to rappel with a Grigri that don’t require a block. I have a whole article about this, read it here. Below is a photo that shows one of several simple methods.
If one person on your team has an ATC, you can simply tie off one strand of the rope for everybody with a Grigri, have them go down on one strand and then the last person unties that knot and rappels normally on two strands.
There you have it: my thoughts on the pros and cons of rope blocks.
Under ideal circumstances with proper anchor hardware, they can work pretty well. But as you can see there are a lot of subtleties to doing it correctly. Once again: I consider this an advanced technique that I highly recommend you practice in a controlled environment with a qualified instructor before you ever try it in the wild. Choose wisely, my friends.