The bowline on a bight, sometimes called "bowline on the bight", is a double-loop knot that makes a pair of parallel, rigid loops that may be used individually if desired.
The knot originated from the bowline, a centuries-old maritime knot still used in activities like sailing, climbing, and rescue operations.
Advantages
The bowline on a bight can be quickly and easily removed by first loosening it and then rolling it back away from the standing end, or the non-working portion of the rope.
It is also reasonably easy to untie after being exposed to a load, as in rock climbing. It is one of the two tie-in knots that are being taught by the German Alpine Club (DAV), generally being considered secure.
Dangers
2011 testing shows that the knot might slip when only one loop is loaded. Cavers and canyoneers ought to fasten their cow-tail carabiner through both loops. European cavers widely advocate the use of a figure eight twisted version of the bowline on a bight.
Applications
This knot can be used to provide a toe hold in the middle of a rope; to make an emergency bosun's chair; and to create an upper rope "block" to make a crude purchase by threading the rope round an anchor point and then back up through the loop. It is sometimes used in sport climbing to tie into two anchor bolts independently, or around a tree while rappelling.
This knot is convenient when a dependable loop is required but neither end of the line is available. It's also commonly used as a seat while being hoisted as there are two secure loops as opposed to the traditional one loop bowline. In theory, this knot would make hoisting many people with one line possible. This knot is very popular in caving as it allows the load to be spread between two anchor points, reducing the stress placed on them and providing a backup should one fail. Commonly known as the Y-hang it allows for a free-hang descent and can be easily adjusted to avoid waterfalls or rub points.
As mentioned earlier, this knot can replace the figure-eight knot when tying into a climbing harness by tying a regular bowline knot and then re-threading it, such as is done with a figure eight knot. However, it is critical to use a strong backup knot with plenty of tail beyond the knot, as the knot may untie during long climbs.<!-- Source? The German "Alpenverein" recommends this knot as a save knot for tying in. --> The advantage of using this knot instead of the figure eight knot is that it can be easily untied after a severe fall.
Technique
To tie a bowline on a bight, take the curved section between each end (the bight) and create an overhand loop where the knot will be (see Step 1 below). Pass the bight through the loop on the opposite side it came from, so that it crosses over the standing end of the rope (Step 2).
Next, pull the bight through until it is large enough to engulf the knot and fold it up over the front to allow the entire knot to pass through (Step 3). Hold onto the parallel loops and tighten the bight over the neck of the standing end.
<gallery perrow=4>
Image:Doppelter Palstek-1.jpg|Step 1
Image:Doppelter Palstek-2.jpg|Step 2
Image:Doppelter Palstek-3.jpg|Step 3
Image:Doppelter Palstek.jpg|Step 4
Image:BowlineBightStep1.jpg|View of Step 2 from opposite side
Image:BowlineBightStep2.jpg|View of transition between Step 3 and 4
Image:BowlineBight.jpg|Fully-tightened bowline on a bight
</gallery>
Notes and references
See also
- Double bowline
- List of knots