Updated and revised by Grant Prattley, OTE Rescue 2014.
Based on original work by SARINZ Trust 2005.
We started to research 3-point anchor loading as a result of questions asked by both instructors and students. At the time we could not find any articles or testing on this subject area. To date we have undertaken a small number of tests but enough to give some indications of what works.
The post tackles a practical question for backcountry rescue teams: is 16mm tubular webbing strong enough for anchor rigging, given the appeal of reducing weight in a rescue kit? To find out, the team ran a series of pull tests comparing different wrap-and-pull configurations — Wrap 1 Pull 1, Wrap 2 Pull 2, Wrap 2 Pull 1, and Wrap 3 Pull 2 — across several real-world surfaces: pins, carabiners, smooth rock, sharp rock, and edge-protected sharp rock. A baseline was first established using 25mm webbing before switching to the thinner 16mm webbing to see how it held up.
The post tackles a common assumption in rope work: that a smaller-radius device — a carabiner, mallion rapide, or belay device — produces more friction on a rope than a larger one, since the rope is thought to have more internal resistance as the radius decreases. To find out if this holds up, the team ran friction tests comparing stainless steel mallion rapides at 12mm, 10mm, 8mm, and 7mm, all using the same 8mm static rope. The results are checked against the Capstan Equation, which doesn’t include radius as a factor in the first place.
With rope diameters trending smaller, there’s a common claim that two carabiners create more friction than one for a Munter hitch or a belay device like the Reverso. This post tests that claim across three stages: measuring the coefficient of friction directly, running slow-pull tests on different devices, and finally trying it out on a practical 10m abseil, using both round and frame-style carabiners.