The triple fisherman's knot is a bend knot

Knot

A knot is a method of fastening or securing linear material such as rope by tying or interweaving. It may consist of a length of one or several segments of rope, string, webbing, twine, strap, or even chain interwoven such that the line can bind to itself or to some other object—the "load"...

, used to join two ends of rope together. It is an extension of the double fisherman's knot

Double fisherman's knot

The double fisherman's knot or grapevine knot is a bend, or a knot used to join two lengths of rope. This knot and the triple fisherman's knot are the variations used most often in climbing, arboriculture, and search and rescue...

 and is recommended for tying slippery, stiff ultra high molecular weight polyethylene

Ultra high molecular weight polyethylene

Ultra-high-molecular-weight polyethylene , also known as high-modulus polyethylene or high-performance polyethylene , is a subset of the thermoplastic polyethylene. It has extremely long chains, with molecular weight numbering in the millions, usually between 2 and 6 million...

 (UHMWPE) and aramid

Aramid

Aramid fibers are a class of heat-resistant and strong synthetic fibers. They are used in aerospace and military applications, for ballistic rated body armor fabric and ballistic composites, in bicycle tires, and as an asbestos substitute. The name is a portmanteau of "aromatic polyamide"...

 core

Kernmantle rope

Kernmantle rope is rope constructed with its interior core protected with a woven exterior sheath that is designed to optimize strength, durability, and flexibility. The core fibers provide the tensile strength of the rope, while the sheath protects the core from abrasion during use...

d ropes.

Tying the triple fisherman's knot is nearly identical to the double fisherman's, except for a third wrap before passing the end through each half of the knot.

Testing has shown that a failure mode

Failure mode

Failure causes are defects in design, process, quality, or part application, which are the underlying cause of a failure or which initiate a process which leads to failure. Where failure depends on the user of the product or process, then human error must be considered.-Component failure:A part...

 exists at very high loads with the double fisherman's knot in ropes using Spectra

Spectra

Spectra are conditions or values that vary over a continuum.Spectra may also refer to:* Kia Spectra, a car developed by Kia Motors from 2000-present* Optare Spectra, a bus body built by Optare...

 and Technora

Technora

Technora is an Aramid that is useful for a variety of applications that require high strength or chemical resistance. It is a brandname of the company Teijin.-Production:...

 cores. The sheath of the rope separates at the knot and the high lubricity core slips through the double fisherman's knot. Although the increase in ultimate strength is small, the triple fisherman's knot does not exhibit this behavior. This has led to the recommendation to use the triple fisherman's knot in to avoid this particular failure mechanism.

The triple fisherman's knot should not be confused with the "triple-T fisherman's knot", which is more akin to a one-sided overhand bend

One-sided overhand bend

The overhand bend is a knot used to join two ropes together. The overhand bend is formed by holding two rope ends next to each other and tying an overhand knot in them as if they were a single line...

and has significantly different properties than the triple fisherman's knot.