How MRT systems work
MRT systems will be familiar to VR operators from counterbalance systems , skate blocks and similar techniques .
In an MRT system , the climbing rope is thrown over an anchor and is secured back to the climber forming a loop . An adjustor such as a friction hitch or belay device is attached to the climber and set on the standing part of the rope to control the size of the loop above the climber .
To descend , the climber lets slack through the belay device , the loop becomes larger , and the climber descends . Two metres of tail is taken through the belay device for every metre of descent . If the rope has been cut or damaged , or is too short , the climber may fall off the end of the rope before reaching the ground . Climbers should always have a stopper knot in the tail end of their rope to prevent this .
To ascend , the climber hauls on the standing part of the rope to make the loop smaller and then ‘ takes up the slack ’ with their hitch or device . As should be obvious to experienced VR operators , with a low-friction anchor point the climber will have a rough 2:1 mechanical advantage for this ascent .
MRT systems remain popular with arborists despite the widespread adoption of other approaches . There are several advantages to using MRT systems in trees , including :
• The tree ’ s structure generally offers a wide range of potential anchor points , and it is easy and quick to change between anchor points whilst working without needing to climb to each one .
• The arborist can ascend , descend , and work position easily using a very simple system . At the most basic , just a climbing rope tied back on itself with a Blake ’ s hitch can be used to reach most parts of any tree .
• The 2:1 mechanical advantage makes it easier to for the climber to minimise the load placed on branches they are working on , or to make minor adjustments to work position without adding additional components to the system .
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