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Tensionless Hitch (No Knot Rig)

Description

The Tensionless Hitch is a great way to attach a rope to a tree or other anchor if you will be applying a large force to the rope and need to be able to untie it easily when you are done. 

To tie the tensionless hitch:

  1. Tie a Figure 8 on a Bight at the end of your rope. 
  2. Wrap your rope several times around the tree or other anchor.
  3. Attach a locking carabiner through the Figure 8 Loop and around the rappel strand of the rope.

Situations where you may want to use the tensionless hitch include:

If you want to calculate the force on the knot, you can use the Capstan Equation:

T1 = T2 * e^(μ φ)

Where:

T1 = The load force (rappel side), in pounds or kN

T2 = The holding force (knot side), in pounds or kN

e = A mathematical constant, 2.718281828...

μ = The coefficient of friction, probably about 0.25 for rope on tree (I'm guessing)

φ = The total angle that the rope wraps around the tree, in radians (remember that 1 full revolution = 360° = 2π radians and that the first wrap is actually only 3/4 revolution)

If you don't want to dig out your calculator, you can use this handy table. Just look up the value that matches the number of turns you have and the coefficient of friction you expect and that gives you the ratio of load force to holding force. For example, if you wrap the rope 3 times around a tree with 0.25 coefficient of friction, then your load is 75 times greater than the force on your knot.

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 1,739 7,735 3,025,434
6 1,374 8,367 50,945 70,010,638
7 4,829 40,250 335,524 1,620,094,652

 

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