No.6 Rope Wrench
The Rope Wrench is a unique Descending device. It is important to think of it as a DESCENDING device when designing your SRT system. It plays no part in ascent. It does not form a 'back-up' in any way. The Rope Wrench becomes 'in-active' on ascent. It has a neutral mode.
On descent it functions like the Kong Robot (on the left). On ascent it automatically finds its neutral mode. The Robot has no neutral mode. We cannot ascend with the Robot above our hitch. The Rope Wrench is unique in this regard.
A single line hitch MUST be tied shorter and tighter than on a DDRT system. It says in the Rope Wrench manual that the hitch should be tied to reliably grab the rope but we must be conscious that the hitch may not do this.
In ascension the hitch is loosened by the upward motion of the hitch climber pulley. As we move from ascension our loose hitch should be tended to engage the rope. We consciously do this. If there is a fall from ascension and being that the hitch cord is our sole attachment it is prudent to bring another device into the ascension mode.
Left: Ascent Right: Descent
Here is one example. The back-up is a Kong 'Duck'. It trails beneath the hitch climber pulley automatically. The small rigging plate on the harness bridge stops the shackle and karabiner from clattering against one another.
Here is another. A traditional 'cow's tail' joins the upper ascender to the climber. The ascender is an open shell toothed cam, twigs and leafs are a pain for it but we can easily back the upper ascender up too with a short length of hitch cord.
We should look always for the safer way. As my old boss used to say:"Safety first and money second!"....or was it the other way around?!!