A new technique for bolted anchors
The open-ended quad
There are many safe ways to attach a highline to bolts, but for a long time I’ve been dissatisfied with the style and efficiency of all the usual techniques. I've finally found a solution I'm happy with.
This concept is adapted from an anchor that Pierce Kenji showed me at Smith Rock. I got the basic idea of individually adjustable legs using a girth hitch overhand from him. His version used two sections of rope instead of four, could only attach to three bolts, and was a bit more complicated to tie. This idea also owes something to the quad anchor described in John Long’s climbing anchors book.
Here's a picture of the open-ended quad used in a rig:
How to tie
The open-ended quad is made from four parallel strands of rope, each about 10 feet long. Near the center are two overhand knots tied about 12 inches apart, which define a masterpoint and limit extension. Two strands go to each bolt, and attach with a girth hitch overhand (defined below).
Attaching to the masterpoint
The mainline and the backup can be joined to all four strands in the masterpoint by attaching the connectors like this:
Girth hitch overhand
The open-ended quad has four legs, each being a pair of strands with loose ends (hence open-ended). Each leg gets attached to a bolt using what I'm calling a girth hitch overhand knot. Here's how to tie it:
IMPORTANT NOTE:
DO NOT USE A FIGURE-8 IN PLACE OF THE OVERHAND IN THE GIRTH HITCH OVERHAND! The overhand knot in the girth hitch overhand may seem overly simplistic, but this is a case where more is not better. In particular, do not be tempted to use a figure-8 instead of an overhand, which would result in a much weaker knot! See the discussion and linked test results here: https://www.climbing.com/skills/in-defense-of-the-european-death-knot/
Tie off the tails
As a final precaution, I strongly recommend tying the tails of the girth hitch overhand knot together with the tails from another bolt, using a sheet bend or a water knot. The tails from the four bolts can be tied together in two pairs as convenient. The reason for this is that overhand knot can creep and roll a few inches under very high loads. If the tails are long enough, the knot will break before the overhand rolls to the end (and the strength retention is good, see discussion below). Tying the tails together makes the whole anchor more fully closed and connected, and making sure you have enough tail to tie together also insures that you have enough tail that the overhands rolling wouldn't be an issue anyway.
Testing the girth hitch overhand
Jerry Miszewski of Balance Community graciously performed some break tests of the girth hitch overhand knot. In three trials, he found greater than 80% strength retention compared to the minimum breaking strength (MBS) of the two strands of rope:
Trial 1:
Rope: Sterling 8mm Accessory cord (the rope used in my pictures)
MBS: 16.6 kN per strand
Attachment: 1/2" BC Shackle
Peak Force: 25 kN
Strength retention: 80.4%
Trial 2:
Rope: Sterling 9mm Safety PRO Static Rope
MBS: 19 kN per strand
Attachment: 5/8" Van Beest Shackle (3/4" Pin)
Peak Force: 32.5 kN
Strength retention: 85.4%
Trial 3:
Rope: Sterling 9mm Safety PRO Static Rope
MBS: 19 kN per strand
Attachment: 5/8" Van Beest Shackle (3/4" Pin)
Peak Force: 33.9 kN
Strength retention: 89.3%
Discussion:
Why do I like the open-ended quad so much? Here's a comparison to two other commonly used anchor types. I'll be measuring each technique against these criteria:
- Solid (above all else, should be sufficiently strong connection to sufficiently strong bolts)
- Redundant
- No Extension
- Equalized
- Simple (Easy to rig, easy to inspect, easy to derig)
Backed up sliding-x:
A 4-point sliding x, with individual backup connections to each bolt made with whoopie slings, 11/16” webbing, or similar.
In the normal course of events, only the sliding-x is loaded, providing a nominally equalized anchor. The individual bolt backups prevent extension and provide redundancy for the sliding-x, which otherwise is a single point of failure.
Pros:
- Satisfies all criteria
Cons:
- Not efficient use of materials. The sliding-x provides equalization, but is not redundant and does not prevent extension. The individual bolt tie-offs cover the same ground, so to speak, as the sliding-x. This solves the redundancy and extension problem, but ends up with more total material strength than should be needed.
- Depending on the material used, a 4-point sliding-x may have too much friction to equalize in practice
- Individual bolt backups can be fiddly to install. If tension was ever switched to these backups, they would likely not be equalized
- Does not always keep the weblock horizontal
Big Effing Knot (BFK):
Start with a 4 point sliding-x, then tie a big overhand knot to create a masterpoint.
Pros:
- Simple to tie and inspect
- Efficient with materials (each anchor leg is sufficiently strong, and isn’t doubled as in the backed up sliding-x)
- Fairly idiot-proof (until they invent a better idiot)
Cons:
- NOT simple to adjust. I see people spending way too much time tying and retying the masterpoint knot to get the legs mostly equalized
- Rarely or never fully equalized
- Does not always keep the weblock horizontal
- Can be a BIG pain in the ass to untie if people have been bouncing and whipping on the line
Open-ended quad:
Pros:
- Satisfies all criteria
- Efficient with materials
- Real equalization (at least between pairs of bolts)
- Easy to adjust each leg length individually
- Easy to untie from bolts, even after high loads (I assume that the extension limiting knots are never untied)
- Does keep the weblock horizontal
- Adapts well to unusual bolt patterns (as long as the anchor legs are long enough to reach the bolts)
Cons:
NOT totally idiot proof. The girth hitch overhand knots need sufficient tails, and the tails should be tied off to each other. Catastrophic failure is possible if all of the tails are very short.
Requires dedicated rope that won't be much good for anything besides bolted highline anchors (compared to a BFK that can be tied with a single longer piece of rope that can be repurposed for many things)
Conclusion
The open-ended quad is the most elegant and easy to rig of any bolted highline anchor I've seen. I've switched to it for all of my bolted highline anchors. My only reservation about the technique is that it is possible to leave insufficient tails for the girth hitch overhand knot. Use the open-ended quad at your own risk. If it seems overly complicated to you, the BFK is still a great option.
Questions or comments? Email Ben (at) benps.com
