Editing Knot (section)

==Properties==

===Strength===
<!--[[Knot strength]] and [[Knot efficiency]] redirect directly here.-->
Knots weaken the rope in which they are made.<ref name="Richards2005">{{Cite journal|title=Knot Break Strength vs Rope Break Strength|last=Richards|first=Dave|journal=Nylon Highway|number=50|publisher=Vertical Section of the [[National Speleological Society]]|year=2005|url=http://www.caves.org/section/vertical/nh/50/knotrope.html|access-date=2010-10-11}}</ref> When knotted rope is strained to its breaking point, it almost always fails at the knot or close to it, unless it is defective or damaged elsewhere. The bending, crushing, and chafing forces that hold a knot in place also unevenly stress rope fibers and ultimately lead to a reduction in strength. The exact mechanisms that cause the weakening and failure are complex and are the subject of continued study. Special fibers that show differences in color in response to strain are being developed and used to study stress as it relates to types of knots.<ref name="Greenfieldboyce">{{cite news |last1=Greenfieldboyce |first1=Nell |title=A Knotty Problem Solved |url=https://www.npr.org/2020/01/02/793050811/a-knotty-problem-solved |access-date=3 January 2020 |work=All Things Considered |date=January 2, 2020}}</ref><ref name="Patil">{{Cite journal |last1=Patil |first1=Vishal P. |last2=Sandt |first2=Joseph D. |last3=Kolle |first3=Mathias |last4=Dunkel |first4=Jörn |date=3 January 2020 |title=Topological Mechanics of Knots and Tangles |journal=[[Science (journal)|Science]] |volume=367 |issue=6473 |pages=71–75 |doi=10.1126/science.aaz0135 |pmid=31896713 |bibcode=2020Sci...367...71P |s2cid=209677605 |doi-access=free }}</ref>

Relative '''knot strength''', also called '''knot efficiency''', is the breaking strength of a knotted rope in proportion to the breaking strength of the rope without the knot. Determining a precise value for a particular knot is difficult because many factors can affect a knot efficiency test: the type of [[fiber]], the [[Rope#Styles of rope construction|style of rope]], the size of rope, whether it is wet or dry, how the knot is dressed before loading, how rapidly it is loaded, whether the knot is repeatedly loaded, and so on. The efficiency of common knots ranges between 40 and 80% of the rope's original strength.<ref name="hsok-ch10">{{Citation| last=Warner| first=Charles| year=1996| contribution=Studies on the Behaviour of Knots| editor-last=Turner| editor-first=J.C.| editor2-last=van de Griend| editor2-first=P.| title=History and Science of Knots| series=K&E Series on Knots and Everything| location=Singapore| publisher=World Scientific Publishing| volume=11| pages=181–203| isbn=978-981-02-2469-1}}</ref><ref>{{Cite journal |first1=J.|last1=Šimon |first2=V. |last2=Dekýš |first3=P. |last3=Palček |title=Revision of Commonly Used Loop Knots Efficiencies |journal=Acta Physica Polonica A |volume=138 |issue=3 |pages=404–420 |doi=10.12693/APhysPolA.138.404|year=2020 |bibcode=2020AcPPA.138..404S |doi-access=free }}</ref>

In most situations forming loops and bends with conventional knots is far more practical than using [[Rope splicing|rope splices]], even though the latter can maintain nearly the rope's full strength. Prudent users allow for a large [[factor of safety|safety margin]] in the strength of rope chosen for a task due to the weakening effects of knots, aging, damage, shock loading, etc.  The [[safe working load|working load limit]] of a rope is generally specified with a significant safety factor, up to 15:1 for critical applications.<ref name="grog-reliability">{{Cite web|url=http://www.animatedknots.com/reliability.php? |title=Knot & Rope Safety |publisher=Animated Knots by Grog |year=2010 |access-date=2010-09-14 |url-status=dead |archive-url=https://web.archive.org/web/20150407023208/http://www.animatedknots.com/reliability.php |archive-date=April 7, 2015 }}. "[http://www.animatedknots.com/safety.php?Categ=ropecare&LogoImage=LogoGrog.png&Website=www.animatedknots.com#ScrollPoint Knot & Rope Safety]", ''AnimatedKnots.com''. Accessed April 2016.</ref> For life-threatening applications, other factors come into play.{{Citation needed|date=October 2012}}

===Security===
Even if the rope does not break, a knot may still fail to hold. Knots that hold firm under a variety of adverse conditions are said to be more secure than those that do not.

The following sections describe the main ways that knots fail to hold.

====Slipping====
The load creates tension that pulls the rope back through the knot in the direction of the load. If this continues far enough, the working end passes into the knot and the knot unravels and fails. This behavior can worsen when the knot is repeatedly strained and let slack, dragged over rough terrain, or repeatedly struck against hard objects such as [[mast (sailing)|masts]] and [[flagpole]]s.

Even with secure knots, slippage may occur when the knot is first put under real tension. This can be mitigated by leaving plenty of rope at the working end outside of the knot, and by dressing the knot cleanly and tightening it as much as possible before loading. Sometimes, the use of a [[stopper knot]] or, even better, a [[backup knot]] can prevent the working end from passing through the knot; but if a knot is observed to slip, it is generally preferable to use a more secure knot. Life-critical applications often require backup knots to maximize safety.

====Capsizing====
[[File:Bowline (PSF).jpg|right|thumb|[[Bowline]]]]
To capsize (or spill) a knot is to change its form and rearrange its parts, usually by pulling on specific ends in certain ways.<ref name="hsok-ch10"/> When used inappropriately, some knots tend to capsize easily or even spontaneously. Often the capsized form of the knot offers little resistance to slipping or unraveling. A [[reef knot]], when misused as a bend, can capsize dangerously.

Sometimes a knot is intentionally capsized as a method of tying another knot, as with the [[Bowline#Tying|"lightning method"]] of tying a [[bowline]]. Some knots, such as the [[carrick bend]], are generally tied in one form then capsized to obtain a stronger or more stable form.

====Sliding====
In knots that are meant to grip other objects, failure can be defined as the knot moving relative to the gripped object.  While the knot itself is not untied, it ceases to perform the desired function. For instance, a simple [[rolling hitch]] tied around a railing and pulled parallel to the railing might hold up to a certain tension, then start sliding. Sometimes this problem can be corrected by working-up the knot tighter before subjecting it to load, but usually the problem requires either a knot with more wraps or a rope of different diameter or material.

===Releasability===
Knots differ in the effort required to untie them after loading.  Knots that are very difficult to untie, such as the [[water knot]], are said to "jam" or be '''jamming knots'''.  Knots that come untied with less difficulty, such as the [[Zeppelin bend]], are referred to as "'''non-jamming'''".