Double fisherman's knot

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Double Fisherman's knot

Names	Double Fisherman's knot, Grapevine, Double englishman's knot
Category	bend
Origin	Ancient
Related	Fisherman's knot, Triple fisherman's knot, Double overhand knot, Strangle knot
Releasing	Jamming
Typical use	Joining thin, stiff or slippery lines, backing up critical knots such as the Figure-of-eight loop or Figure-of-eight follow through
Caveat	Difficult to untie
ABoK	#294, #1415

Use the double fisherman's knot to tie together two ropes of unequal sizes. This knot and the triple fisherman's knot are the variations used most often in rock climbing, but other uses include search and rescue.

The primary use of this knot in rock climbing is to form high strength loops of cord for connecting pieces of the rock climber's protection system. It is favoured for being compact, and for arranging the line of force in a straight line through the knot.

Another common use for this knot is to back up a critical knot, such as a harness tie-in knot or single-line rappel rigs. In this use, the running end is tied around the standing end of the rope, so that it cannot slip back through the knot.

This knot is also used for tying necklaces. Instead of two separate ropes use one, and tie the two ends together. In this way, you can tighten and loosen the necklace without breaking the strand.

Dyneema/Spectra's very high lubricity leads to poor knot holding ability, and has led to the recommendation to use the triple fisherman's knot rather than the traditional double fisherman's knot] in 6mm Dyneema core cord to avoid a particular failure mechanism of the double fisherman's, where first the sheath fails at the knot, then the core slips through.^[1]^[2]