On Thursday the low pressure weather system Dieter dumped quite a strong winter storm on us, which in combination with snow on trees caused a number of failures. Consequently Friday turned out a bit busier than I had anticipated, clearing storm damage.
One call out was interesting, part of a fir tree had broken out at the base due to included bark and was leaning on a three storey building. I only had photos to go on beforehand, so we loaded up plenty of gear to cater for a range of eventualities.
The part of the tree which had failed turned out to be reasonably sizeable and the inclination in which it was learning against the building was quite flat. Luckily the remaining part of the tree was sound at the base and high enough to place rigging gear – whilst still retaining an efficient angle to winch the piece off the roof. I placed a large Impact Block at the high anchor point, attaching an arborWINCH line though the hollow spindle, then down to the failed failed part of the tree, to which I attached a small Impact block, making sure the angle between the line and the axis of the stem was more or less 90°, to ensure maximal efficiency when winching. From there back up to the high anchor and down to a GRCS.
Next, before moving anything we secured the base with 16mm Sirius rigging line, rigged a floating anchor on which we had a Port-a-Wrap to blocks of concrete on the roof, from this we rigged a control line down to the tree on the building and in the other direction we installed a further rigging line, with a mechanical advantage system rigged to it.
Then we tensioned up all the lines, lifted the tree off the roof, used the control line and the MA system to move the tree to one side and lower it.
Not rocket science, admittedly, but none the less something you could come unstuck on. A couple of observations here: I love working with arborWINCH in non-dynamic rigging situations: This 12mm rigging line with a braided Dyneema SK78 core is super-lightweight yet strong and adds an extra level of control to a job like this. Using conventional Polyester rigging lines, you would spend more time winching to tension the line, the whole rig is more spongy and less responsive. Using arborWINCH, once you have taken up tension and the knots are cinched up tight and bedded down, you have a very high degree of control when lifting and lowering.
Where possible in a rig like this it can be a good idea to do away with knots, to secure the butt of the stem, for instance, we simply took wraps with the rigging line around the base of the remaining fir before ending the wraps with a clove hitch. In case the butt did kick out, this would dissipate the energy in a much more rope-friendly fashion, compared to a knot.
Finally, storm damage is notoriously fraught with risk. Ensuring the highest degree of control possible makes a lot of sense and allows you to take a step backwards if things do not move forwards as planned. In this case the two lines either side of the stem allowed controlled lateral movement, the arborWINCH controlled the up and down movement.
Add to this the fact of having enough competent people on site, taking the time to talk the plan through, designating roles, defining danger zones, considering what might go wrong and not rushing it, then indeed, it is not rocket science. On the other hand, if you did cut corners and tried to simply bosh it out, things could quite easily get… dynamic and dramatic – not my idea of an ideal end to a Friday…
Thanks to Flurina and Vito for the photos.