Treetools has seen a couple of very dramatic 'tests' recently which demonstrate how easily the Rope Wrench can be pulled down onto the friction hitch, in theory sending the climber plummeting to the ground.
Try is yourself. Set up the Rope Wrench system anyway you prefer, without any load applied.
Now imagine a branch dropping onto the Rope Wrench pushing it down onto the friction hitch.
The Rope Wrench acts like a tending pulley in reverse, releasing the bite of the friction hitch from the rope. You'll soon see how easily the whole system slides down the climbing line.
This is a VERY DRAMATIC demonstration, hence its regular use by Rope Wrench critics!
Unfortunately, while the theory is sound, the Rope Wrench actually behaves quite differently in practice.
As soon as the Wrench is correctly set and a load (your body weight) is applied to the system a 'kink' or 'bend' will appear in the climbing line.
This is a result of simple physics in action (if there is such a thing as simple physics?).
The 'bend' is produced in the climbing line when leverage is applied to the Rope Wrench via the tether attached to its outer 'arm'. Downward force is applied to the lever when the climber puts his weight into the system.
The 'bend' provides the necessary friction to stop the friction hitch from binding onto the single leg of the stationary line during descent.
The same 'bend' also stops the Rope Wrench from sliding down, tending the friction hitch in reverse (as experienced in the dramatic test described above). The friction generated at the pins is so great you could almost use the Rope Wrench as a hand ascender.
Throughout all the tests conducted by DB Tree, in conjunction with Treetools, we have not been able to replicate the results of this dramatic demonstration with a climber on-board.
Some 'Wrenchers' have told us of friction hitches not setting during ascent with the Rope Wrench (when load is applied).
The solution appears to be in the 'setting' of the Rope Wrench before any load is applied (assuming your friction hitch is correctly tied, dressed and set).
Ideally, climbers should get into the habit of sliding the pin-end of the Rope Wrench up the climbing line until it can go no further - BEFORE they load the friction hitch - this seems to work every time.
>Thanks to Drew Bristow from DB Tree Splicing for the above Rope Wrench set-up using the DMM Ultra O, DMM Pinto, Ocean Polyester 76cm 8mm e2e and the DB Tree Quick-Release Tether