Observatory de Gonneville

[The Thing]

Hi All,

A long post and long overdue.

Some of you will know I have moved to France, and some of you will know that I have been intending to build an observatory. This summers project has been to get started while the builders (another story) were off site for their August vacation. While they are working it's not possible to get access to the garden so as soon as they were gone I got digging.



As you can see one of the problems on the site is a lot of groundwater. The Obsy site is about 20m from a stream at the bottom of the garden. When it rains for a period the ground becomes saturated. It is sandy loam and drains well but also fill up well (did I mention we have a well?). The rebar rods are driven to the bedrock and are 3m long. The string is so I could tell if they had stopped going down when hit with the lump hammer.



The bottom of the hole was lined with a bit of hardcore and concrete and then builders rebar offcuts (very handy) assembled for the pier. The tube is 25cm x 2.5m aircon duct. The top is made of M16 rod and concrete formwork ply (thanks again builders) which is tough as old boots and has already been in the garden for 6 months unscathed. The length is wiggle room for roof angle, clearance and so on. When I am sure I will cut the rods down or fill in the gap with concrete using a tube offcut as a mould. I may also get a steel plate made up at that time to replace the ply.



You might be thinking 'I know Duncan is tall but that is a very long pier tube". The wall behind is 3.35m tall and to the north east. The floor of the Obsy will be 1m up. The front wall will be 2.9m-ish tall to the roof, a section of this wall will roll back with the roof. With this combination I will be able to a)see Polaris b) be above most of the wet layer of air that forms above the garden thanks to the stream. Also I can store stuff underneath.



This is where I am now, there are now also paving slabs on the gray marl. Because of French planning and tax rules the shed can only be 5m2 and temporary so no concrete base or you have to get planning permission and pay tax.

The structure is going to be made out of the pile of reclaimed joists you can see in the background. A frame flat on the slabs will spread the weight and I'm going to use adjustable legs so that if the shed starts to sink (a real possibility when the ground is very wet) I can level it up and keep the roof rolling. The front corner posts will be double thick joists so I can mount my StarAdventurer and possibly my HEQ5 on them. If I want a second permanent pier like Mark, I'll put  a twin obsy next door!

I'll have to work on the structure as soon as the builders have cleared off each day. Watch this space.

[MarkS]

Excellent report and great photos!

That pier is certainly a "Duncan height" pier!

I'm assuming that the big square hole is now full of concrete?

Mark

[Carole]

Interesting read this is going to be an obsy and pier with a difference.

Carole

[The Thing]

I'm assuming that the big square hole is now full of concrete?

Mark

Definitely full of concrete and steel. Topped with bubble wrap and polystyrene and overlain with weed proof garden stuff which I've used to wrap up the edges of the gray marl and keep it contained. The wet sandy ground is one reason I haven't gone for a concrete slab as it would need to be thick and may not be stable if it started to tip  -  we've had to have enormous house foundations to the bedrock for just this reason!

[The Thing]

Interesting read this is going to be an obsy and pier with a difference.

Carole

It will be different! The floor will be at the height of the ladder platform.

[JohnP]

Looks great Dunc - I also look forward to seeing the progress & on the upside if you get 'peckish' while observing you can always stick your arm out observatory roof & grab an apple    John

[The Thing]

Progress, the four poster is now formed and I have been playing with the rather over specified flooring (more joists!). As soon as I cut the floor bits (hard work cutting joists even with a motorised saw :{) I can use the pier!

The long beam on the ground will be the front rail support for the roll off roof. The back rail will have another 2m section added and be fixed to the wall using a French outbuilding door hinge piece about a foot long that is made to set in a stone wall. It has a vertical 1.5cm thick pin at the extremity which I will fit in a hole in the beam. I can then shim it up and down to get the level. I have found Brico Depot to be the place to get more reasonably priced rails and wheels (for sliding gates), otherwise they are twice the UK price. Trip to Cherbourg then.

I will make hinged frames around the bottom to allow access to the 'cellar' space, and fixed frames and the all important door in the top section, all clad in tongue and groove. The roof will come down around a meter vertically at the front so that section of the wall will roll away. Thus there will be clearance for the scope for those that were wondering.

Last night was very dewy and there was a definite low misty layer, up on the obsy floor I was above it! Design criteria one validated.

[MarkS]

Nice write up but the image didn't load

[The Thing]

Nice write up but the image didn't load

For some reason I am not able to get a working link off Google Photos like I could last week. So I've put the picture in the good old gallery!

[Rocket Pooch]

I'd knock that wall down and cut down the tree's if I were you.

Nice hole.....

[The Thing]

I'd knock that wall down and cut down the tree's if I were you.

Nice hole.....

I have plans for the trees and maybe a few copper nails next door to the south west , the daft old git seems to be trying to create a pinetum.

[Carole]

Can't get any sense of size Duncan, any chance of a photo of the construction with you in the photo?

Carole

[The Thing]

HI Carole,

The base is 2mx2.5m (6ftx8ft ish) to be within French shed planning regs. The pier is 2m high to the blue bag which is where the threaded bar sticks up and that is 25cms in case I have to have wiggle room to get the roof past the parked scope.  I will set the rods in concrete when I have the height sorted. The top of the wall is 3.35m and the roof will just be visible from the other side. The joists are 65mm x 175mm and despite being at least 30 years old and having been in the garden piled up for a year are in excellent condition. So it's very solid.

The walls will be filled in with battens and covered in T&G. The bottom sections will be hinged to allow access to the 'cellar' which will be a place for astro gear and probably the lawnmower. The beer fridge may be down there as well! Power will go in when and outlet is available on the side of our house.

I'm planning a roof sloping at 8deg which will be the same as our new house and of a similar metal sheet (but a lot cheaper than zinc). The front section of the shed will be able to roll away as it will be part of the roof. There will be hinged section to fold down at the SE end (trees at the back are NW, wall is angled NE so N is over the wall).

Hope that fills in the gaps!

[Fay]

Well done Duncan, great progress and the tallest pier in the land!!!!

[The Thing]

A quick update. I have lowered the floor 20cms since I wouldn't have fit under the roof - don't quite know how my plans and measurements got me there! I have also nailed on a couple of bits to approximate the roof line to make sure I can stand under the roof!

I also used the pier with my HEQ5 Friday and Saturday nights. Being up off the grass is certainly a lot warmer and hardly any dew on things despite the grass getting saturated. Last night it was great being able to hook up the laptop and slew straight to objects with no messing about. Just shows how much tripods settle on grass, I could have it polar aligned one night and off the next. Maybe it was the moles.

I will be shortening the threaded rods by a lot as Polaris is way up over the wall and I can only just reach the top of the dew shield when parked. I will be setting a custom park position. I just need enough clearance to do up the bolt for the EQ6 or I can do as Mark does and bolt the baseplate to the scope and then fit it over the rods.

Next steps are order the lames (tongue and groove cladding to you and me) and some other bits of wood to make the roof and side structure, roof panels and fixings, rails and wheels. Then a couple of days banging and crashing it all together!

Some pictures later on...