The BOB in anchors
If you don’t know what I mean by BOB, the intro post is required reading.
Anchor options with the BOB
There are four main types of anchors I construct using a BOB.
V and W-style anchors
Quads
Banshee belays
SWAMP anchors (while a possibility, there are better options)
V and W anchors are what they sound like: you make a V (two pieces) or a W (three or more), then tie a masterpoint. Overhands, figure-8s, and even figure-9s are common masterpoints. However, a BOB is an option as well.
V-style BOB anchor
Start with an overhand, then flip it into a BOB.
The quad is ubiquitous by now, but it is almost always tied with overhands serving as the limiter knots. These are incredibly hard to untie. Additionally, quads are commonly tied with a 240cm sling, aka a quad length. This name doesn’t come from the anchor style, but instead because it is four times longer than a shoulder length sling (60cm). In fact, tied with overhands, the quad is best constructed with a triple length sling (180cm). But with BOBs on either end, a quad tied with a 240cm sling lands at an ideal length for belaying from above.
Quad with BOBs
This anchor is tied with a 240cm sling. When using overhands, I tie my quads with a 180cm sling.
Banshee belays aren’t the standard in the United States, but they are popular in other parts of the world. A BOB tied in one end of a double length sling (120cm), provides enough space to clip everything you want, plus enough tail to reach the other bolt. When using this method, I tie a clove hitch with both strands of the standing end, then clip back the bight to keep it out of the way.
Banshee belay
Note the necessary locker attaching the BOB to the lower bolt. This primary bolt must be solid. A clove hitch to a non-locker can be used for the secondary component. There should be minimal slack between the components. The tail of the clove hitch is clipped to the non-locker to keep it out of the way.
The SWAMP (shelf without a masterpoint) is an anchor that has fallen out of favor recently, being replaced by the much easier to untie options provided by clove hitch and girth hitch masterpoints (at least when tied with slings). However, if you want to create an anchor with extremely limited materials, the SWAMP made with the rope still shines. While you can use a BOB for this purpose, I highly recommend only doing so when both standing ends are loaded. The bunny-ears figure-8 is a better choice for situations like leaving fixed lines. Both knots are reasonably quick to tie, easy to untie, simple to adjust, and use minimal materials. The BOB however has a failure mode that occurs if the secondary eye is transversely loaded without the primary eye also clipped. For this reason, I advocate for the bunny-ears figure-8 since the BOB only offers marginal advantages while introducing a costly failure mode.
Pros of the BOB in anchors
The main advantage of the BOB is its ease of untying. No longer will you have to gnaw at a knot to break down your anchor. Another benefit is getting your masterpoint higher, allowing for a more ergonomic belay from above. Finally, a BOB creates twice the number of strands at the masterpoint compared to a traditional knot. This means you can have two (or more) independent full-strength and redundant clip-in points; you can even offset them to create separation if you wish. These additional points for attachment means your anchors can be less cluttered and nothing will be trapped when you attach multiple people, ropes, or bags to the anchor.
W-style anchor
A BOB doubles the number of strands at the masterpoint. With three components, it creates six loops which allows for three independent masterpoints.
V-style BOB with offset masterpoints
You can adjust the length of the eyes to further separate your masterpoints.
Cons of the BOB in anchors
Of course, nothing good comes without compromise. A higher masterpoint and those multiple clip-in points use up more material, meaning you may not be able to tie a BOB given the position of your components and the length of your sling or cord. The BOB is also notably more difficult to tie than an overhand. If I use overhands, I can tie a quad in maybe 10 seconds. Using BOBs for the same task takes more time and concentration. It’s pretty hard to mess up an overhand, but a BOB requires you to pull the appropriate strands to tie correctly. Under stress this may be challenging. Again, while the BOB can be used for a SWAMP anchor I recommend a bunny-ears figure-8 instead to avoid a potentially catastrophic failure.
