The Unicender by Rock Exotica is an all-in-one ascender/descender that works in both single and doubled rope techniques (SRT and DdRT). This unique “mechanical split-tail” designed replaces the friction element (tied hitch) of a DdRT tree climbing system. Invented in 2005 by arborist Morgan Thompson and now produced by world-renowned machining phenomenon Rock Thompson of Rock Exotica, the T6 alloy Unicender also functions cleanly on single line for abseiling and is not limited to use by professionals only— recreational or beginning climbers will find it a rewarding investment for occasional to regular use as well.
The Unicender is considered inherently less complicated than separate ascender and descender devices because there is no dangerous changeover at the top of the climb, affording seamless transitions from ground to crown and ground again.
Here’s how the Unicender works on doubled rope: With your climbing line attached to the top of the Unicender and the tether below attached to a saddle, weave the falling part of line as diagrammed on the device. From here it’s identical to the traditional technique except there’s no need to advance or even handle the Unicender until you’ve reached your destination. It magically advances with near frictionless motion, towed by the (upper) attached line. Descending is performed one of two ways—in “squeeze-to-go” mode or “rope slide” mode. In squeeze-to-go mode, you descend or limb walk by pinching the activation bars together. Squeeze hard—go fast. Squeeze soft—go slow. Release the device and it locks on line. Rope slide mode is most commonly used to descend single line (SRT) and is performed by lapping a bite of exiting line around the activation bars and tailing the device, much like tending a figure 8. Very simple, very smooth.
Under heavy weekly use by practicing arborists and with relatively grit-free lines (utilizing a friction saver above), the Unicender has been found to last 18 months or more before requiring replacement of the four clamping blocks or retirement all together. These parts naturally erode from rope abrasion.