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Friction Hitch Fundamentals

by Paolo Bavaresco for "Landscaper" magazine 2000.

Probably the most important component of a climbing system is the lowly friction hitch. It is needed for safety in ascent, work positioning and descending. It is cheap to replace and as of yet has no mechanical equal. It is often surprising to many that tying the same piece of line in a slightly different configuration can have such an effect on hitch performance! The aim of this article is to enlighten those that feel their ‘Prusik’ hitch offers the same performance as a ‘Machard Tresse’ (French Prusik).

"In the beginning, God created Herr Prusik, and Herr Prusik created a hitch that Arborists would use".

And so it is written in the Tree Climbers Bible. However, the Prusik hitch has disadvantages and innovative climbers have succeeded in overcoming them. It is difficult to credit any one individual as the inventor of a knot as like minds invent alike, name their invention differently and then argue about who thought of it first. The names given to hitches in this article are the ones commonly come by.

Before delving into the specific performance of each hitch, the basic physics of climbing systems must be understood:-

  • Imagine a lifeline passed over a branch and connected to a climber’s saddle with a bowline and friction hitch (as in the body thrust technique). The climber’s weight is supported by both the hitch and the bowline, meaning the friction hitch only has a force of half the climber’s weight acting upon it. This is likely to be reduced by the friction of the branch holding some of the weight. Using a friction saver will put more wear on the friction hitch.
  • If the same rope is now passed over the branch and the friction hitch is tied around both legs of the rope, the climber hangs only on the friction hitch (as in the footlock or single rope technique). All of the climber’s weight is applied to the friction hitch. Depending upon the type of hitch used, this climbing situation may require one or two extra wraps to be taken to hold the additional weight. Some hitches, when tied as an ‘open system’, should never be used in this situation. No friction hitch should be used as a sole means of descent if all of the climber’s weight hangs from it.

Open & Closed Systems

Some friction hitches can be tied open or closed, which affects performance. For example, a Prusik can be tied with a single length of rope and secured with a figure of eight stopper knot. This is an open system. It can also be tied into a loop or both legs tied onto a karabiner. These are closed systems.

Types and Diameter of Prusik Cord

The mountaineering rule of thumb is that whatever line is being climbed, a Prusik cord half the diameter is required for a positive grip. However, this rule is for climbing a single rope and only applies in arboriculture to the footlock and single rope technique. When using a friction hitch in the body thrust technique, only half the climber’s weight needs to be held, as already established. This enables a hitch to be effective using a cord of the same diameter as the climbing line. The American ANSI standards require a minimum hitch cord diameter of 12mm. This prevents the use of many of the better performing hitches that I shall mention later. However, FASTCo 401 recommends a minimum rope diameter of 10mm. Most of the hitches photographed for this article were all tied with a 130cm length of 10mm double braid and secured with a double fisherman’s knot. Friction heat wouldn’t be a problem in the footlock, so kernmantel rope can be used (not as hard wearing as braid). Smaller diameter braids suffer more from friction heat than larger diameters. This is not the case on an adjustable lanyard. With some hitches, this heat can be felt through the hand. Dynamic Kernmantle cords may offer better performance than static braids but typically don’t wear well.

The Prusik

This is the traditional hitch used by British climbers and popularised by Merrist Wood College by using a two-ended rope technique with Prusik loops. These loops aid hitch performance and safety. Loops also prevent the hitch from loosening too much when left hanging between changeovers. The Prusik grips somewhat better on 3-ply than it does with braided arborist rope. However, this can be remedied with 10mm diameter braids and by tying a 6-wrap Prusik instead of 4. Can be loaded from either direction. Prusik lock hampers slack tending with the fair-lead pulley. Can be used for the footlock with 6 wraps.

The Prusik Soube or Schwerbisch Hitch

Similar in performance to a Blake’s hitch but tied as a closed system. Doesn’t tend to lock up like the Prusik and can be loosened easily. Cannot be tied with a loop. Will only grip in one direction.

The Klemheist

Similar in performance to the Prusik Soube. Normally tied with a loop. Will only grip in one direction. Can be used for the footlock with 6 wraps.

The Tautline

Tends to roll when tied open. Tends to grip tightly but more difficult to loosen than a Prusik, hence poor fair-lead pulley performance when slack tending. Must not be used as an open system for securing the footlock. Cannot be tied with a loop but can be tied into a loop, or both ends can be secured, as in the photo, for a closed system.

Blake’s or Polish

Works well with 12mm braid, hence popular in America. Can be adjusted to any length for long body thrusts or branch walking. Grips without jamming and free slides with a fair-lead pulley. Cannot be tied in a loop or as a closed system. Will not roll out like a tautline but should be secured with a stopper knot. Works well with the footlock but should be tied with 5 or 6 wraps instead of 4. Will only grip in one direction.

The Distel

Tends not to jam or slip. Can be tied long or short. Must be tied in a closed system. Very responsive. Will grip equally well on a single line system. Will only grip in one direction. Free slides with fair-lead pulley for slack tending and grips positively. Can be tied with any length of cord.

The Machard Tresse (loop) / Valdotain Tresse (cord with eye each end) or French Prusik

Must be tied in a closed system. Can be tied with a loop. Never jams. Very free sliding – it’s either on or off! Doesn’t always grip instantly if tied to long or with too thick a cord. Never jams even in wet conditions. Will only grip in one direction.

The Bachman or karabiner jamming knot

Must be tied as a closed system. Must incorporate a locking karabiner. Normally tied with a loop. Good performance on wet ropes. Can be used with a fair-lead pulley. Will only grip in one direction.

One method of body thrusting using these short hitches is to pull hand over hand above the knot, and then hold with one hand whilst pulling under the fair-lead pulley with the other to remove slack. Semi-footlocking automatically slides the hitch up via the fair-lead pulley. Very easy to set up as an auto prusik system.

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