Tensionless Hitch

[burnsdye]

I recently got an email asking for some elaboration on how the tensionless hitch (http://dyeclan.com/outdoors101/canyoneering101/?page=tensionless-hitch) works. I understood the concept, but I didn't fully understand the mathematics behind the setup. So after some research and thumbing through my old calculus textbook, I am happy to report this simplified load table that I calculated out.




Number of Wraps
T1/T2



μ = 0.2
μ = 0.25
μ = 0.3
μ = 0.5


1
3
3
4
11


2
9
16
27
244


3
32
75
178
5,650


4
111
362
1,174
130,741


5
391
1739
7,735
3,025,434


6
1,374
8367
50,945
70,010,638


7
4,829
40,250
335,524
1,620,094,652




T1/T2 is the ratio of the force on the rappel strand to the force on the knot.
μ is the coefficient of friction.

When would you ever use this? I don't know. Get creative. Maybe at the bottom end of a guided rappel? Search and rescue situation? Thoughts?

[dougr]

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[Kuya]

I know you might think this is a "simple" table. but for the non-math nerds out there, can you explain this in kindergarten terms that I can understand haha :crazycobasa:

[Taylor]

In simplest terms: If you wrap the rope around the anchor(tree) once and have low friction, there will be nearly equal force on the knot and the load strand. If you wrap it seven times and have high friction, there will be practically no force on the knot and all of it on the load strand.

If interested in why this matters or in the concept of the tensionless hitch, I will explain further.

[oldno7]

I usually rig a tensionless at the top of Yankee Doodle with a 200' rope.
It allows you to get in the first 2 raps off this.
Although, I did have someone tie our rope to a tree at the bottom of the first rappel once.
Tensionless is non-retrievable, you are leaving a rope at a particular spot.
I usually go 8-10' down the rope(depends on diameter of tree)and tie a figure 8.
Then wrap the tail end around the tree however many times you wish and then re-thread the figure 8.

[2065toyota]

What is the advantage of something line this over say a stone knot


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[Bo_Beck]

In rescue terms, a high strength tie-off is used to maintain the integrity of "full strength" in a system. If a system is to be built to an inherent strength of 30kn, assuming that carabiners, rope, anchor and any other components in the system are 30kn. If the rope is rated at 30kn, and a knot is introduced into the rope then the rope strength at the knot is reduced by roughly 30%. By using a "high strength wrap (friction) " or prusik bypass to eliminate force at the knot, the rope then maintains its 30kn integrity and isn't a weak link in the overall system. Commonly, if not always this type of rigging is used when setting up "Highlines". The introduction of the "MPD" has sort of changed thinking in the rigging of highlines to a degree though, but the use of overall system integrity for maximum strength hasn't. A couple photos of prusik bypass, high strength tie-off, and highlines that require full strength integrity.

[ratagonia]

Using a tensionless hitch is fast and easy, and does not require untying a tensioned knot when breaking down the rig.

That said, it depends upon the rope/object friction. There are things out there with very low friction such as steel pipes and very smooth logs. More wraps will make this less of a problem.

Tom

[2065toyota]

A stone knot is not really a knot, but a hitch.
Would it not serve the same purpose and is easier to tie?
Does that type of hitch reduce the strength of the rope as knots do?
Just curious if anyone has any info on that. Not that it matters very much. Thanks

[ratagonia]

A stone knot is not really a knot, but a hitch.
Would it not serve the same purpose and is easier to tie?
Does that type of hitch reduce the strength of the rope as knots do?
Just curious if anyone has any info on that. Not that it matters very much. Thanks

A Stone Knot is relatively new, thus could take 50 to 100 years to work into SAR protocols. It would have the same loss of strength of a normal knot, so a loss of 20% to 40%.

Tom

[Bootboy]

A stone knot is not really a knot, but a hitch.
Would it not serve the same purpose and is easier to tie?
Does that type of hitch reduce the strength of the rope as knots do?
Just curious if anyone has any info on that. Not that it matters very much. Thanks

A hitch is technically a category of knots. The term hitch refers to a knot that is used for tying or terminating a rope to an object.

A knot is simply a manipulation of a rope, cord, webbing etc..., that serves a function.


LNT