ART of Canyoneering

Saturday, 5 Feb 11. Spent much of the day in St. George playing with some new toys and new ideas. Borrowed a friend’s dynanometer to do some pull tests on the Canyon Cordelette. No intention of breaking the cord; just wanted to see how much load the hitch could hold before slipping and whether or not the hitch could be released under load. Pulled on Canyon Cordelettes made with three different types of cord, plus two standard Purcell Prusiks.

Single Strand Canyon Cordelettes
3/2 wrap Prusik, 7mm Nylon Cord (New England) Rated: 2300 lbs
3/2 wrap Prusik, 7.5mm Hybrid PER (BlueWater) Rated: 3372 lbf
3/2 wrap Prusik, 8mm Technora PER (BlueWater) Rated: 4046 lbf

Standard Purcell Prusiks
3/2 wrap Prusik, 6mm nylon (New England) Rated: 1650 lbs X 2 = 3300
2/2 wrap Prusik, 6mm nylon (BlueWater) Rated: 1888 lbs X 2 = 3776

Premature Slippage
The 2/2 wrap BlueWater nylon Purcell Prusik slipped at approx. 140 lbs. Likely due to the 2/2 wrap Prusik. This Purcell was not included in any subsequent tests.

Releasable Under Load
We used a 4:1 MA to load each rig to 200 lbs, then 300-340 lbs. All of the hitches could be released under load. The 8mm Technora PER required the most effort to release. Likely because the Technora surface is not as sooth as the other materials. The ability to release under load is a useful attribute for things like transferring load when passing knots in haul systems, rescuer repositioning during tandem rappels and pick-offs, etc.

Maximum Load Before Unintentional Slipping
Surprisingly, all of the hitches slipped at approximately the same load, 660 to 680 lbs, except the Technora PER, which did not slip until 770 lbs. This slipping is not considered a bad thing as it acts as a kind of pressure relief valve. Better to have the hitch slip under load to absorb energy than to have the cord break.

The hitches all slipped approximately 2-3 inches, then stopped slipping on their own because the slippage caused some of the tension to come off the system and reduce the load. The slippage also created enough heat to fuse some of the hitches to the cord. The nylon fused and could not be moved without completely untying the hitches. The polyester portion of the Hybrid PER fused, but could be moved upon partially untying the hitch. The Technora portion of the Hybrid PER did not fuse due to its high heat resistance. The Technora PER did not fuse at all, but the hitch had cinched down tight enough to require partial untying to move it.

If slippage occurred under a continuous static load, the hitches might continue to slip until fusing stopped the slipping or until the loop closed completely.

If slippage occurred under a dynamic load, the hitches would be expected to perform like a normal Purcell Prusik – the slippage would absorb some of the energy. As the load is reduced, the hitch will stop slipping.

And … it was fun.

Rock Exotica developed two new figure eight devices – the mini and the micro – for special ops teams. I managed to get my hands on one of each and have been experimenting to see if I can come up with canyoneering applications.

The photo shows the mini eight rigged as a releasable block. Haven’t rappelled on it or lowered anyone with it, but it seems quick secure even without a safety carabiner added.

The loop going over the neck would be the lowering mechanism. I made a twist in the rope on the brake strand before looping it over the two horns. Kinda like a cleat hitch.

Uploaded instructions for Rigging a Releasable Block using the Totem.

Rigging the rappelling rope with a releasable block provides some distinct advantages: (1) setting the rope length allows for simple disconnects at the bottom of the rappel, (2) the releasable system can be used to lower a rappeller from the anchor if the rope is not long enough to reach the bottom, or if hair or other material becomes stuck in the rappelling device.

The stone knot (AKA stein knot) is used to isolate two strands of rope. It is useful to gain efficiency on short rappels where more time is spent by people rigging and de-rigging their rappel devices than is spent on the actual rappel. Using the stone, while one person is rappelling, another person can be rigging. As soon as the first person is on the ground, the second person can start rappelling and a third person can start rigging.

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