The sessions in Japan last week were interesting.
The suggested topics were anchor points for the sessions in Ina and rigging systems for the Maruichi training in Ooka. I went into the events with an outline, an introduction, a whiteboard, as well as various bits and pieces of gear. I also had a PowerPoint presentation for the anchor points session as a plan B, but actually today I really prefer to use PowerPoint in homeopathic doses – if at all. However, I was glad in this case of having it there, as the prequel to typhoon Trami dumped copious amounts of rain on the venue in Ina, so we split the day into an indoor session in the morning, with discussion revolving around the PowerPoint, in the afternoon we installed various systems in the space above the ODSK shop.
The interesting thing I find about running workshops with only a rudimentary framework in place is that they force you to be reactive to the location and people around you, as well as taking you places you do not expect to end up in.
For the rigging session in Ooka, we went on site the day before and discussed what we could install where. Based upon that, I came up with an outline, which was to build a “simple” system on the first day and a complex one on the second day. The simple system would involve snatching a log onto a block, the complex system would be a full-blown high line. The idea was to explore how we plan and configure each of these options, the components we use and to discuss the challenges that each presents. On the first day we set up a test-bed, took a 200 kg log off the top of a spar and spent the afternoon doing fully static drops into the rigging system, using 10 and 12mm Teufelberger Sirius, as well as a 12mm HMPE rigging line. I was interested in seeing what kind of forces would occur, how the rigging system would respond the repeated loading, whether we could induce a failure – and if so, where this would occur.
We also filmed the drops, this was only partially successful, the GoPro filming side-on proved to be a bit temperamental, but we got some good footage regardless. A number of interesting observations were possible based on this:
- Peak forces were around 15kN, with the HPME line producing lower peak forces, which was unexpected. However, it seemed that due to the material being slippery, the line slipped through the attachment knots, buy doing do dissipating force.
- The Port-A-Wrap was all over the place during the first part of the drop, lots of movement going on there. Obviously, if you are trying to generate as high a forces as possible, a fixed bollard would be preferable, however, we did not have a suitable one at hand. This footage certainly emphasises the need to get Port-A-Wraps as tightly snugged up as possible.
- The shots from below clearly show the pushing-backwards movement of the stem as the log pushes off and how it is pulled forwards as the log is caught by the rigging system. A further interesting observation is how the slow oscillation during the first part of the drop is cancelled out by the counter-oscillation when the movement travelling down are cancelled out by the movement travelling upwards. This happens after the log impacts onto the base of the stem.
- The shots of the base of the tree clearly show the shock waves travelling outwards through the root system, the energy being dissipated into the ground.
This in itself was interesting, as there was all kind of variability that was unexpected. This was not least due to the fact that the stem had a bit of a lean on it. Without a doubt this in itself soaked up a lot of energy. We dropped three times onto each line, the 10 and 12mm Sirius, i.e. a polyester double braid, as well as onto the HMPE line, which was a 12mm hollow braid. None of the drops resulted in a failure, there was some glazing, but nothing overly dramatic.
What this demonstrated though is that something that is superficially simple may not be. When dynamically snatching onto an anchor point below the mass, there are so many variables in play that it can be hard to predict how it is going to play out. The first day in Ooka cleary demonstrated this.
The second day, we discussed the plan of how we were going to rig the high-line…
Then we went out onto the site, laid the components out on the ground and started to build them into the two anchor trees. We were using one of DMM’s Offya trolleys on a 16mm polyester high line, with a low-elongation pure polyester line for lifting and lowering, the control lines were non-descript 12mm lines. The plan was to use the high line to dismantle the spar we had left standing the day before from the rigging system testing.
Visibly, people were struggling to wrap their head around the set-up, however, when we broke it down into its constituent components, step by step, and started running lifts, with two people on the control line top and bottom, one person on the lift/ lower line, one person cutting on the spar and one person coordinating the lift, things came together nicely, by the end running smoothly, with the mass being moved in a coordinated fashion laterally and down simultaneously.
What these days demonstrated clearly was how simple systems, depending upon how closely you examine them, may well turn out to be not quite that simple – and that complex systems can be broken down into sub-systems, which are neither that complex, nor that hard to understand.
A big thank you goes out to all who attended these sessions and to those who made them possible: Kinshita-san at ODSK and Iwasa-san at Maruichi, as well as the Poynter family for their hospitality and Takashi Osaka for his fantastic translation skills. It would not have been possible without you all…