Windy conditions for observatory

[Dwarf Nova]

Location: Orkney and exposed.

Since I got the concrete base down for my 2.2m pulsar dome I have experienced some very strong winds (averaging 50mph and gusting 70mph) - and I believe it gets stronger.

This has caused me to pause  for thought (panic) before I assemble the dome.

I would appreciate any advice on offer about how to ensure that the cupola is not ripped when the wind gets up.

So far I have obtained a set of four M12 anchor-bolts and am fiddling with ways to shackle the  cupola to the concrete base; and I would love

to hear from anyone who has a feeling for how to get a strong connection to the fibreglass.

[Stub Mandrel]

Do the makers advice on the best fixing points, or do you just have a  broad flange and a choice of where to drill for hold-down bolts?

I would make sure you use large washers, or even better long spreader plates between the bolt heads and the fibreglass flange, to ensure that the holding down bolts spread their load over a good section of flange. The anchors should be flush or even slightly below the top of the concrete.

Try to place them near reinforcing seams where any flexing will be minimised. I would be tempted to consider extra bolts.

Use a waterproof silicon in a thick bead between the concrete and the base of the dome, but consider having a drain at some point because water will get in!

[Peter Drew]

Can't really add anything to the good advice already given but I would emphasise the need for large washers or spreader plates to give a better load spread on the fibreglass which can be prone to splitting. 

[Dwarf Nova]

Thanks for reassuring advice.  Perhaps it would help to insert flexible gaskets between fibreglass and metal of washers/spreaders to mitigate pressure points.

[Peter Drew]

Sounds a good plan. 

[Ibbo!]

I think I would want more than 4 bolts holding it down TBH

[Stub Mandrel]

Bicycle inner tube would probably be a good sources of material - too thick and flexible and you'll undermine the benefit of a spreader.

[steppenwolf]

For what it is worth, I have the very same Observatory and although I am not on Orkney, we have had some lashing storms here in West Sussex and the dome roof has been solid as a rock. I have two lock-down bars inside the dome (standard supply but you could always fabricate a couple more or order an extra pair from Pulsar - I'm sure they'd supply them if asked). In the strongest of storms, I did note that the aperture cover itself did rattle under very strong gusts but that's all and I have never had any water ingress.

For my money, I'd dispense with location points and simply buy two caravan awning straps (for my sins, I am also a rough weather caravanner) and attach them crossing over either side of the aperture to spread the load.

[ollypenrice]

Yes, I think that, since you won't be imaging or observing in a hurricane, a hurricane-proof*  'exceptional circumstances' system is probably the answer and something like hefty straps or webbing over the outside removes the worry of localized stress on the attachments. 

Olly

*I do realize that nothing but a deep cave is ever likely to be truly hurricane-proof!

[steppenwolf]

*I do realize that nothing but a deep cave is ever likely to be truly hurricane-proof!

Olly, I thought the Les Granges storm caves were a closely guarded secret? Did you mean to disclose this?

[Owmuchonomy]

I can vouch for the Awning straps described by Steve.  Together with the angle iron pegs and damping springs they offer great wind protection.  We have to use them on our Autumn trips with the tin snail to the Northumberland cliff site we use.

[Horwig]

I've been out checking the obsy tonight. Might not be Orkney rough, but it was bad enough here. The clatter of the shutter was not good!

I also use a strap over the whole dome, better safe than sorry.

H

[Pompey Monkey]

Even down here on the South coast it's been a bit rough. I am only slowly building confidence in my Keter 6*4 shed, even though it's well anchored down!!!     

[laser_jock99]

My neighbour recorded gusts of 70mph last night. And yet another 'farm subsidy sized'  wind turbine burned out (second time in twelve months for this one....) last night. They seriously need to think about sighting these things in less exposed sites!

[michael8554]

If you go down the large steel washers and gaskets route, make sure the straps are at 90 degrees to the bolts, to minimise the load pulling the bolts and washers out of the dome surface.

Michael