The Bowline on a Bight, an Introduction
The mention of a bowline in climbing circles can be contentious. Either it’s a dangerous knot banned by gyms that you don’t know how to confidently inspect (and therefore shouldn’t use), or it’s the saving grace that allows you to untie from your harness after whipping on your project. But I’m here to introduce you to the single bowline’s cousin, the bowline on a bight, or the BOB
why a bowline on a bight?
There are many ways to create a fixed eye, so why use a BOB anyway? Firstly, it’s much easier to untie than an overhand, figure-8, or even figure-9. If we’re expecting high loads, using slick material, or tying with webbing or slings a BOB is going to come out without resorting to gnawing at the knot with your teeth or smashing it with a hammer. Second, the BOB doubles the number of eyes compared to most bight knots. This can be helpful because it creates redundancy and uses more material (useful for raising the height of masterpoints).
on a bight or with a bight?
A very common point of confusion when the word “bight” is mentioned is the distinction between on a bight and with a bight. First, let’s define a bight. A bight is a section of rope that forms a 180° curve . It is created in the middle of the rope. When you tie something on a bight (also referred to as “in the bight”) you are tying it without access to the ends. Doing so creates a stable circle of rope of unchanging size. In contrast, knots tied with a bight are creating an artificial end with a bight. The knot is then tied with the bight as if it is end of the rope, with the strands forming the bight always staying together, acting as one. If you like mnemonics, you can think about the “O” in “on” creating a circle you can clip (just like the knot); the parallel lines found in the word “with” remind you a knot with a bight is tied with twin strands.
bowline anatomy
Now that we have the on vs with distinction taken care of, let’s talk a bit about bowlines themselves. A simple bowline has a nipping loop, an eye, a collar (which I call the tongue), a loaded strand, and an unloaded tail. The nipping loop is the part that cinches down. The eye is the part you could clip with a carabiner or place around a tree. The tongue wraps around the loaded strand of rope exiting the bowline. The tail is the end of the rope within the bowline. There are numerous variations on bowlines, from ways to lock them, to handedness, to even the orientation of the components. For us right now, it’s just important to understand the individual parts so we have a shared starting language. If you care to learn more, you can read an excellent analysis on bowlines from the Professional Association of Climbing Instructors, an Australian organization, as well as a variety of papers on other knots.
how to tie the BOB
The simplest way to tie the BOB in my experience is to start with an overhand on a bight. Once made, flip the loop over the body of the knot. This loop will become the tongue. Examine the knot to determine which strands of the core lead to the tongue. Pull these while also applying tension to the standing ends (the rest of the rope). If done correctly, the eye will be stable. If you made a mistake, the eyes will either shrink or expand.
Start with an overhand
Flip the bight
Pull strands to make the bight smaller. It helps to also provide tension on the standing ends.
A finished BOB
considerations when using the BOB
Make sure you actually tied a BOB! It is extremely common to pull the wrong strands when attempting to cinch down the tongue of the bowline. If done incorrectly, you essentially make a girth hitch (which could be catastrophic depending on how you’re implementing the BOB) instead of a pair of stable fixed-size eyes.
It is best practice to always clip both eyes of the BOB. The eyes can be of different size and can be clipped to different things, but they both must be loaded in unison. In certain circumstances clipping only one eye can lead to failure of the knot (most notably ring loading the eye leading to the tail).
It is permissible to ring-load the BOB, despite the same loading profile leading to failure in other bowline variations, including the commonly used simple bowline. The BOB can handle a single load in the eye, a load in two locations across the eye (while no load exists on the standing end), as well as many loads pulling the eye in multiple directions.
However, the BOB cannot handle loads if the standing ends are pulled in opposite directions. This makes the BOB a poor option when loads are expected in different directions (think glacial travel).
possible applications of the BOB
I’m finding more and more uses for the BOB in my both my personal and guided climbing. Here are a few examples to get the ideas flowing for where you might want to implement a BOB yourself.
Limiter knots on quad anchors
Masterpoint for V and W-style anchors
Banshee belay anchors using both slings and the rope
Rappel Extensions
Lowering from single-pitch climbs
Tying into the middle of rope when both standing ends are loaded either in parallel or independently (e.g. for the leader climbing in parallel)
