Dome build: The Deluge!

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After a night of heavy rain I went out to check the dome under its tatty, old,  lightweight tarpaulins. The rain was still falling like stair rods but I had donned a waterproof jacket for protection. I climbed up into the dome and looked around. All seemed to be well apart from the constant dripping from the bare, tarpaulin area over the open slit.

A smaller tarpaulin, which I had carefully placed across the top of observation slit as extra insurance, was literally full of water. A huge bulge had collected at the very top inside the dome!

My mind immediately flashed back to when I was a toddler. A neighbour had kept his motorcycle under a tarpaulin stretched between two outbuildings. Not the wisest policy given the material's ability to collect heavy rain. I clearly remembered that he had pushed mightily upwards with a large wooden pole. In a desperate bid to clear a vast lens of bright water over the nearest available edge. This had not ended well. 

The pole had instantly penetrated the tarpaulin resulting in a huge deluge in precisely the wrong place. The poor pole bearer and his motorcycle were thoroughly drenched! The elapsed time and increasingly fuzzy memory does not retain the exact details of his verbal cries of consternation. 

With all this firmly in mind, I climbed the tall, guyed stepladders to the zenith. There must have been easily ten gallons suspended just beneath the still roaring roof. I tentatively removed the crossbar which had caused the temporary dam. With the quite unexpected result of receiving an early, very cold shower! There was also an immediate and thorough wetting of the previously dry observatory floor. And so on down to the ground floor through the once carefully spaced floor boards. Ah me.

I retired indoors across the heavily puddled lawn/outdoor workshop/parking space to replace literally all of my clothing. Needless to say The Head Gardener was not well pleased. Having to supply two complete sets of clothing, to the overgrown child, is quite beyond her formal job description.

The moral of this story is to build some shutter doors to close off the large gap in my protective adns supportive dome. A proper, heavyweight, PVC tarpaulin would have been a good idea, earlier on, but cost and weight had been a major worry. 

The circumference of a hemisphere is Pi x D/2. Or Pi x R if you prefer. 3.142 x 3/2 . So [say] about 5m per side of a square tarpaulin to only just cover the dome. 6x6m would have been about right to cover the bare midriff but nobody lists a square tarpaulin except as made to order. Not to mention the weight at nearly 3/4 of a kilo per square meter. Then the heavy friction of the tarpaulin on the dome as I heave it upwards via a rope. While simultaneously perched atop the soaring stepladders, in the open observation slit. As exposed as some WW1 flying observer in a string-bag "kite" over the Front Line.

Even lifting two lightweight 4x6m tarpaulins, tied together via the eyelets on their long sides, are near my physical limits. This is due to heavy friction on the bare and bristly plywood with the woven material. Any damp raises the grain and then there are the sharp angles between the facets. Add some wind and it all gets very silly, very quickly indeed!

Yet, if I don't keep the dome completely dry I can't seal, nor prime and paint it before winter really sets in. I could arrange a heavy tarpaulin into two opposing rolls and then shove it out of the slit. So that the tarp unrolls itself naturally in opposite directions. Except that, increasingly cold PVC tarpaulin is stiff and a dome is nothing like a normal, double-pitched roof. The friction of unrolling itself, largely unsupported, might actually be worse than dragging the whole thing upwards with a rope from the veranda!

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