Dome build: A bit of a storm in a bucket.

 *

I have invested in a safety sling to use as a climbing belt. My multiple strands of rope belt was clumsy and uncomfortable. The sling needed a figure-of-eight knot to use up some slack but was fine after that. I put a caribener through both ends of the loop and clip my scaffolder's hook and tether onto that.

A great improvement on the rope but certainly not worthy of serious, professional use or rock climbing. I have no plans to fall more than a foot and am being extremely careful at all times. It just provides me with slightly more confidence when I am working right at the top of the ladder. I clip onto the top rung to limit any fall to an absolute minimum. My head is rarely above the top of the ladder and the tether kept short and taut.

Friday and it is already windy with showers promised. The gale forecast has dropped to 20m/s or 45mph gusts on a 12m/s or 25mph base. I have to cover the door openings with ply to stop the dome inflating and pushing off the shutter cover. I didn't want to cover the shutters individually because of the rain running between them.

BTW: Never trust tarpaulins to be remotely to the stated dimensions. There is a Chinese billionaire banking on your not measuring his ephemeral wares with a tape measure. My 3x4m tarpaulin was 10cm or 4" short of any consumer law worth the virtual paper it is written on. Ironically I needed exactly 3m to fit the shutters. So I had to cut it from the 4m length.

I also covered the veranda doorway and the main entrance with stapled, reinforced PE. I had to fix them on the inside so I could escape. So I added some crossbars to stop them blowing in during the storm.

Just for the fun of it I hung a 1lb weight on a thin cord from the obs. floor to see if the building was moving. Since it was so windy I hung the weight in an empty bucket to protect it from direct external influence. A real pedant perfectionist might have added damping fluid too but I forewent that finer detail.

The problem with this experiment is finding the resonant frequency of the building and matching the pendulum length [and therefore its period] for maximum sensitivity. I was limited by the presence of the ground but had no immediate plans to dig a deep hole for the bucket. Conversely I might have tried shortening the pendulum but that would have meant finding something on which to place the bucket.

It now occurs to me that I could monitor the building's longer term behaviour with a pointed plum bob over something immovable like a large nail point protruding from the gravel floor. There are plenty of non-trafficked areas to set this up. Any relative movement would suggest subsidence.

In the time since the building and pier have been standing I have only once felt the need to adjust the pier jacks for increased clearance from the observatory floor. This amounted to only 1/4" at 10' above the ground. So was hardly dramatic.

Click on any image for an enlargement.

*