Page 32 - Rappelling

Cord Comparison. Top to bottom: Bluewater 5mm Titan Cord tied with triple fisherman’s knot
(Dyneema core/nylon sheath, tensile strength 13.7 kN or 3,080 lbs.); Sterling 6mm Powercord tied
with triple fisherman’s knot (Technora core/nylon sheath, tensile strength 19 kN or 4,271 lbs.);
Sterling 7mm Nylon Cordelette tied with double fisherman’s knot (nylon core/nylon sheath, tensile
strength 12.4 kN or 2,788 lbs.).

strand breaking strength of around 19 kN (4,271 much more quickly (losing strength) than good
lbs.); and the 5mm Tech Cord, sold by Maxim/ old- fashioned nylon. In his study, a flex cycle test
New England Ropes, with a 100 percent Technora was performed on various cordelettes. The cord
core and polyester sheath, rates at a whopping 5,000 sample was passed through a hole in a steel fixture,
pounds tensile strength. flexed 90 degrees over an edge, and loaded with a
However, at the 2000 International Technical 40-pound weight. The steel fixture was rotated back
Rescue Symposium, Tom Moyer presented a paper and forth 180 degrees for 1,000 bending cycles,
titled Comparative Testing of High Strength Cord that then the cord’s tensile strength was tested (single
revealed some startling deficiencies in Technora strand pull test) at the section that had been flexed.
and other high-tech cords. Testing showed that The Technora sample showed a remarkable loss
with repeated flexing aramid fibers break down of nearly 60 percent of its strength, while Sterling

Equipment 21

Rappelling_i-174_3pp_CS55le.indd 21 7/24/13 10:15 AM