What's a worst case scenario force during a guided rappel in canyoning?
Well, I thought it would be during a rescue from the bottom. There are a lot of factors that come into play when calculating (guessing) the expected forces in rigging a system like this. So many factors that it's almost impossible to determine in the field. This is one type of rope systems that can generate a lot of force.
We wanted to know how much force and what our margin of safety really is.
This system was rigged from two 55mm Triplex bolts in shear "equalized" to a master point at the top. The bottom anchor was equalized with a Dyneema 60cm sling to two 55mm Triplex bolts in shear. All bolts were placed in solid granite. The rope we used for the guide-line was a BlueWater Canyon DS pro. The rope Joe was rappelling on was the 6mm Petzl PUR line which gives a nice smooth decent on a system like this.
If you are curious about how strong the Triplex bolt are, check this video out 👉🏼 👉🏼
I used two different techniques (one poor technique 😂) to simulate what might actually happen in a bottom up rescue. Since more force is created when ascending, we did not run a rescue from the top. During the simulated rescue, the top anchor saw a peak force of 4.8kn both times, the bottom anchor saw a peak force of 5.07kn.
There are more ways, and better, to execute a rescue on a guided rappel. Rigging using releasable systems is a good place to start. The best option is not to need a rescue at all.
Tensioned systems like these are high risk and you should have good training and an understanding of rope systems before using a tensioned system like this.