Sometimes when setting a up a top rope anchor, you may have great anchors that are far back from the edge of the cliff. A good solution here, especially in a teaching setting where there are probably extra ropes lying around, is to use two completely different ropes, one for the anchor (also known as a “rigging rope”) and one for actually climbing.
This is also known in some circles as the “Joshua Tree System”. Joshua Tree is a wonderful climbing area where this rigging is especially handy, because good anchor points are often far back away from the actual edge of the cliff.
While you can use a normal dynamic climbing rope, ideally this anchor rope is static, to limit any significant stretch. Even so-called “static” ropes have a little bit of stretch; they are actually about 25 percent dynamic. (So it’s not like you’re climbing on a steel cable, a common misconception.) You can get quality static rope sold by the foot / meter. To start, 30 meters may be a good length. If you often find yourself in an instructional setting, it can be a worthwhile purchase.
Here’s a sample of various flavors of static rope sold by the foot from a major online web retailer. 30 meters of rope should run you about $60-$70.
A static rope is preferred because as the weight of the climber goes on and off in the rope, the rope will stretch and contract, moving up and down over the edge of the cliff. If the rock is reasonably worn or rounded, that's probably not going to be a problem. But if it's something more abrasive, it could potentially damage the sheath of the rope. (Static ropes also tend to have a more durable sheath.)
You can mitigate potential rope damage by putting an empty backpack or tarp or something similar under the rope at the cliff edge; see image below.
Or, if the rock you're on is especially sharp, such as Joshua tree granite, you might want to use a designated rope protector. Cutting up an old garden hose or using some bulk 1/2 inch heater hose from the car parts store is a sturdy and inexpensive way to protect your rope.
If you don't have a static rope, no worries, a normal dynamic climbing rope is usually going to be fine.
Here’s one way to set this up:
Attach each rope end to a super strong anchor, which could be a multi piece gear anchor, stout tree, or a large boulder. (If you have a single absolutely bomber anchor, such as a large tree, it's fine to use that single point also.)
Holding both rope strands, carefully approach the edge of the cliff properly backing yourself up with a friction hitch.
Tie an overhand on a bight in BOTH strands, also known as a BHK (Big Honking Knot). Tie the BHK just past the cliff edge, so the loop hangs down toward the base of the route. Put some padding under the rope as it runs over the cliff edge if you think there’s any chance of abrasion. (See photos below.)
The BHK is the key move. The BHK is an elegant solution, because it distributes load equally onto the two strands, along with being entirely redundant. (If you try to set this up without tying a BHK, and instead start fiddling around trying to equalize separate figure 8 on a bight knots or clove hitches in each strand, you’ll soon realize how frustrating this can be.)
You will probably have a good sized loop of leftover rope after you tie the BHK. You can ignore this, just toss it off to one side. That is another elegant subtlety to this anchor, you really don't have to worry about how long your rope is. Fix the ends each to something solid, tied the BHK at the cliff edge, and ignore whatever leftover rope you have. Done.
Now, while you’re at the edge of the cliff, properly tied in, you can add a couple of opposite and opposed locking carabiners, thread the second actual climbing rope through them till you get to the middle, and then toss both rope ends down to the bottom. You’re ready to top rope.
OK, not a real cliff here, but use your imagination. The “cliff edge” is the wooden fence. (And yes, I am using a dynamic rope.) Each end of the rope is securely attached. A sling and locking carabiner is around the blue bike rack, and a bowline is around the huge tree.
Stand at the “cliff” edge, tie a BHK in both strands, add a stout locking carabiner or ideally two, and you’re done. Ignore the extra rope that’s looped off to the left. To make your anchor a little more tidy, you could pull the extra rope back from the master point and just tie it off with an overhaNd knot on one of the strands to get it out of the way.
Close up of the BHK and carabiner. Ideally, you can use two opposite and opposed locking carabiners at the master point. (But many people are fine with one.)
Briefly, let's run this anchor through the anchor acronym checklist of SRENE (Solid, Redundant, Equalized, No Extension)
Solid? Check, you're using the climbing rope and each end is attached to something bomber.
Redundant? Well, this is kind of interesting. We're only using one rope, but because of the BHK, it isolates each strand and makes it perfectly redundant.
Equalized / Distributed? Yep. Force on the anchor is shared between each strand of the rope.
No Extension? Got that too, it's tied like a huge cordelette so there will be no extension if any aspect of the anchor were to fail.
Let's look at a couple of instructional photos / diagrams of similar setups, and compare them to the rigging above.
In the photo below, the two rope ends are properly secured, with a BHK at the master point. But look what's happening with all the extra rope - it's piled up next to one of the anchors. What if you need to move the master point a foot or so in any direction? You're going to have to mess with the knot on the two cams on the left strand, which is going to change the amount of slack in that strand, which is going to affect your load equalization / distribution. Not so good.
(This set up would work if you attached the right rope strand around the boulder first, then walked down the right strand to tie the BHK, and then went back to secure the left strand to the 2 cam anchor. This set up works fine, but it’s an extra step compared to the method above.)
The set up used in the photo below would be a good choice if you wanted to use the extra rope on the left to make some sort of tether for an instructor, so they could belay themselves close to or even over the edge to keep an eye on the climbers coming up. But, if you are a top roping exclusively from the bottom of a route, this is not needed.
The diagram below has most of the core components correct, showing use of a static rope, a pad at the lip secured with a prusik, and two carabiners at the master point. Overall, this anchor is fine as shown.
But there’s no BHK at the master point. Instead, there’s two figure eight knots, then a clove hitch on the tree. Trying to dial in the load equalization / distribution is going to be a bit more of hassle, but overall this anchor is looking pretty good.
If you try setting it up like this, remember to do it in order. 1) fix the left strand of rope around the boulder, then walk to the edge and tie in this case the two figure 8 knots, and then step three, walk to the tree and tie the clove hitch to equalize the right strand.
Personally, I find just fixing it and then walking to the edge and tying a BHK to be the simplest and least fussy, but there are several ways to approach this. The important thing is, be creative and use that extra rope if you have it.