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Sunday 1st 12.00 54/52F. In the time it took me to set up for a sunny clearing, it had passed into solid overcast. The weather is windy and coming from the south west. Two very distinct layers. A fast moving lower layer and higher one moving much more slowly.
I cleared the collection trays of over 12 litres of water into two buckets while I waited for the cloud to clear. The rainwater was spread on the ground to feed all the willows to the west of the observatory. Any shelter is welcome and they are very dense.
14.00 The imaging never happened. Constant overcast. I can see the telescopes have stopped automatically at the meridian. As I look across at the open dome after lunch.
A storm is crossing the North Sea overnight and will provide SW then Westerly gales and solid rain for Denmark tomorrow. Some sunshine is promised for Tuesday but still quite windy.
14.30 Teaser blue patch. I manually flipped to Home and then onto the other side of the pier. More hours passed without a sign of the sun.
Eventually I gave up and prepared the dome for tomorrow's promised 45-50mph gusts. First I point the closed and heavily clamped shutters into the expected wind direction. [SW.] Pointing the shutters downwind might cause them to lift with suction. Then I hung four ratchet straps from the zenith board's, heavy eye bolts. The other ends are hooked under the bottom of the 18mm [3/4"] plywood, pier cladding before tensioning. The pier cladding adds up to a full 8'x4' sheet of heavy ply. [2440x1220]
The combined 56' of splayed, timber, pier legs are heavy lengths of 4"x4". There are also four, hefty, concrete anchors buried in the ground and bolted to the four timber "feet." Not to mention the massive home-made equatorial mounting with its 50mm shafts and counterweights. Plus at least 50lbs of telescopes on top of the mounting on top of the pier.
The dome is always secured against lifting by eight, thick disks attached to the steering wheel brackets with strong bolts. These are arranged around the massive base ring so very unlikely to let the heavy, plywood dome lift. So the tensioned ratchet straps are just extra insurance. A heavy PVC tarpaulin is draped over the horizontally parked telescopes and upper pier. Just in case of a dome, panel failure. Again only likely through wind suction. There are multiple screws and adhesive holding each panel in place on its sturdy framing.
The severity of forecast gusts has now been reduced. Peaking at 18ms as of this evening's forecast. With a conversion multiplier of 2.2 that's about 40mph.
I was looking at screw type, ground anchors by Indusfix Helankers. My tall observatory has quite a small footprint [3m Ø] for its considerable height. It rest on eight, equally spaced concrete anchors around the circumference. These have steelwork to screw to the eight, 4"x4" timber uprights.
A couple of ground anchors and sturdy cables, at an appropriate angle, might be well worth the relatively small investment. The area to the west of the building is heavily populated by densely planted, multi-stemmed willows of several colours and varieties. So would provide ideal ground conditions without ever impeding foot traffic. The area is now all but impenetrable on foot after several "haircuts." Though it would not be too difficult to trim the willows just to clear the tensioned cables.
The idea of ground anchors has been on my mind since I first built the observatory. I could fix some hefty eye-bolts through the exposed, veranda joists to carry the load into the structure. We have never had another "Storm of the Century" like we did back in December 1999. That did severe damage with 35ms gusts. 75mph+.
With the forecasts for ever more severe weather, in future, it might be well worth beefing up the building's resistance to wind. Sou-westerly and southern winds are most common. Though [presumably] a storm has the potential to blow from any direction.
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