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Unicender developments

Richard Tregoweth - Tuesday, October 13, 2009

Over the last few months Auckland contract arborist, Johno Smith has been trialing the Thompson Unicender introduced to New Zealand by Treetools. Johno is an SRT fan and had previously worked out a system using a prussic, figure-of-eightand a DMM Revolver to efficiently move about the tree - now, the Unicender has taken him to a whole new level.

Johno used the Unicender in the 'aerial rescue' at both the Hamilton and Wellington TCC events held recently and found it saved a lot of time not having to change rope systems. For these events Johno had the Unicender attached to the extendable bridge on his Treemotion but that configuration still required plenty of changes in position - lengthening and shortening the bridge. Since then Johno has trialled a chest attachment, originally with the Petzl Secur, to hold the Unicender in a constant vertical position while he footlocked into the tree. But the Secur kept lifting up under his chin so he has since changed to a 'used' bicycle tube. Don't laugh, it works! The stretch in the rubber allows for body movement without too much pressure on the shoulder blades. Once in the tree he unclips and he's away.

In his original configuration, Johno found extreme limb walking sometimes produced 'bounce' on the branch when returning. To overcome this he has modified the system by attaching a Wild Country Ropeman (or ISC Micrograb), a rated webbing sling and DMM Revolverto the line and converting to a double rope for the return. The pulley on the Revolver and the mechanical advantage gained through the double rope technique ensures an effortless return, no rope slack in the system and therefore no branch 'bounce'.

While developing the above configuration Johno noticed the rope sometimes slipped out of the Unicender rope guide and the friction on the bar was inhibiting smooth movement (Johno thought a Revolver style pulley would solve the problem). Morgan Thompson, the designer and manufacturer of the Unicender has made some modifications to accommodate these ideas (see picture below).

One unanswered question relating to the Unicender is its safety rating and possible use in a National Tree Climbing event. Morgan has advised Johno the Unicender tested end-to-end to a breaking strength of 7000 lbs - 2000 lbs above the industry ANSI standard. The tests were carried out by IMR TestLabs in the USA. The Unicender is designed to slip on the rope at 1200 lbs using SRT. This is a safety feature for the rope, the Unicender and more importantly the climber.



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