Specialised Stage Engineering: Picture an average gig. The truck doors open, a bustle of activity explodes around the truck as stage hands push boxes to where they need to be and the riggers are in the air rigging chain hoists for the truss. It’s a simple show, 1 span of truss upstage and downstage with moving lights suspended by two 500kg hoists each.
Except, today, they added 2 LED screens to the upstage truss. Nobody mentioned to the head rigger that this was happening and the schedule is tight already. He eyeballs the screens, figures that his truss might be overloaded with that load on such a long span and so he adds a third hoist to the centre of the span to take up the extra load.
3 comments:
I was working on a crew rigging a 30' rig to the ceiling in a lobby, with moving lights and light bars and a bajillion feet of socapex cable. We realized that the socapex and light bars combined weighed more than we had anticipated, and we would need to rig extra chain motors. The TD had an extra chain motor around, but had to call his contact at the rental company to get two larger chain motors because of this exact rigging problem. Handy things to know.
This is one of those things in physics that defies what a common sense solution may seem to be. This just goes to show how letting unqualified people rig things overhead is just a really bad idea that could quickly become catastrophic. I wonder if this means that there are no fly system with only three points attached to the batten? This is something I'd be interested in further exploring.
This just reinforces some information I was given when we had a guest speaker Bill Sapsis. He referred to this exact situation as a indeterminate structure, and from the information we were given can be very dangerous. He did not have a clear answer to handle a multi wench rig which is in every day use around the world in all kids of applications of entertainment. This issue is something that should be taken very seriously, research should be done, and ones du-diligence should be done when entering into a multi-hoist situation. The chart was quite helpful but I wonder how accurate the chart is in everyday use. So currently I will be calling and refering to someone else if I personally confronted with a multi-wench situation.
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