Mechanical advantage systems for branch walking and work positioning
One reason many arborists prefer MRT is the 2:1 mechanical advantage that is provided when returning from a branch walk with a poor rope angle . Rescue climbing systems are not designed for this style of climbing : descenders such as the CT Sparrow or Petzl I ’ D operate with the tail emerging from the device on the opposite side from the climber . Tending this slack means pushing the tail away from the climber , increasing their weight on the branch .
Where branch walking must be conducted with a poor rope angle , the installation of some form of mechanical advantage system can assist with work positioning and returning along the branch .
In the image above , the climber has installed a 3:1 mechanical advantage system by passing the tail of the climbing rope back through a pulley attached below an ascender above them on the line .
Systems like this can be installed when required at the end of the branch , however in this case they must be adjusted every time slack is captured .
Recognising the need for a 3:1 mechanical advantage system and installing it in the correct place ahead of time can assist with returning from a thin branch , or in working with a poor rope angle .
Note that the tail of the climbing rope below the pulley must be captured and retained by the climber - if it is lost then no mechanical advantage has been gained . In the image above , the climber is using a short sling choked to the attachment point of their harness , which can be snapped on to the running end of the climbing line so that it does not pass out of reach .
Some devices do not allow slack to be captured when the handle is in the ‘ lock ’ position . If using this technique take care not to create a ‘ dead leg ’ – where the climber is hauling in on the tail of the line but not capturing the resulting slack . This could expose the climber to a dangerous shock load or pendulum swing .
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