Poly water tanks as Astro observatory

[Gargoyle_Steve]

I went to post this as a reply to the comment by Arthur (nightsky) in the "Little Prefab Dome" thread but realised it may be of interest to others who may not see this info there so I've set it up as a new thread instead.

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I've been investigating the polywater tank solution for ages now and it's too easy to NOT go ahead with using a poly water tank as the basis for an observatory if you really want or need one, and can't be bothered building it all yourself.

Thee's a wide variety of tank diameters, heights, and colours readily available, they are solidly built, UV protected and available all over the place from numerous, often local, suppliers!

This is one company that can have tanks delivered over a very wide area for instance.
http://www.polyworld.com.au/rainwater.htm
(scroll down to "medium tanks" for some interesting models)
Here's a few other interesting links with sizes, colours, etc:

http://www.rainkeepertanks.com.au/polytanks_bushmans.php

http://www.irrigationwarehouse.com.au/category284_1.htm

http://www.teampoly.com.au/Pages/main_products_tank.html
Apparently I can get a tank ith 2.55 metre diameter & 2.4 m height delivered to my location, inc GST, for approx $2000. I haven't seen a price on a proper dome that compares to that elsewhere and I think the mods to convert it to astro use per my requirements will be pretty darn inexpensive.

The ONLY reasons I don't have a tank observatory already is that my back yard doesn't have enough free space, and I don't really need it presently with my dob! When the day comes, I think this IS the way I'll be going.

Cheers!

[Orion]

I think using a water tank is a great idea.

[GrahamL]

I think you could probably build something for a fair bit less than 2 k steve.
Those tanks get there strength from the ribbing on the roof and base
If you were to cut through or remove any of the supports it would
likely get pretty wobbly and start turning into a major hassle to
make it work ..Imo:)

[Omaroo]

I'm with you Steve because I've seen it done. The guy left the bottom in, placed the whole shebang on a sandy base. This makes it a very stable and solid floor once its packed down. He used 6 deep star pickets inside through the bottom of the floor to then secure it to. He has cut the roof and rivetted a strip of steel inside the bottom edge (of what is now the roof) so that is sits on the outside of the rim below it. The whole roof weights 15kg or so so he just lifts it off when needed. A standard door and frame are screwed in to the side with a curved lintle at the top to match the roundness of the wall.

Downside is that it's not at all secure. I'd pour a few hundred inches of concrete inside the base of the floor to make it more solid if I were doing it, but it's all feasible.

[[1ponders]]

Sounds like a good idea, but try getting a rainwater tank up here atm. There is something like a 16 week wait. :eyepop:

[Dennis]

And tank manufacturing/holding sites are being broken into with new tanks being stolen.....

Cheers

Dennis

[nightsky]

No Worries Steve
G'Day,
As a after though,when I had bought all the material, :doh: I was thinking that I should have bought a Water Tank,a plastic one about 2.1 mt across and about 2.4 high, was $1100 incl shipping anywhere from W'Gong to Newcastle,then all you had to do was to cut the floor out,cut out a door,cut out a slit for the roof.You can get them in white and off white and will never leak,and with the floor that you just cut out,just cut a hold in the middle the width of your pier,slip it over the pier and Bob's your Uncle,so much easier and quicker and no hassle, with a few heavy duty casters on the bottom and thats it,put it on concrete or a wooden platform.BTW is does not have to be plastic,tin would be just as good, but would need a little more work than the plastic one's
Cheers
Arthur
P.S. Here's the thread http://www.iceinspace.com.au/forum/showthread.php?p=219337#post219337

[nightsky]

G'Day,
Yes you can get them cheaper than $2K (see above) in NSW anyway,to over come the support side of it.make sure that get buy one with no seems,but if you can't it don't matter,as you can always erect a small frame inside,after all most of the work has been done for
Cheers
Arthur

[Miaplacidus]

Maybe someone should talk to the poly people. If we could all agree of general specs, perhaps they could modify one of their designs specifically for use as an observatory.

[nightsky]

G'Day,
I did ask them and the reply was. "It's just not worth it,having to change over all there setup just to make a few Observatory's,besides there flat out with the demand for water tanks"also they would have to cope with different designs and colours and it's such a small market.Which is fair enough I suppose.
Cheers
Arthur

[ballaratdragons]

There is a Plastic Poly Tank factory just near me, and I asked them about getting them to alter the mold in minor ways and they said 'No Way'!

They sell seconds for about $2500!!!!! Too much!

[bojan]

Some time ago I did some calculations for DIY dome, based on frame and canvas approach (geodome)....
For 2.5m diameter, this looks like in the file attached.
2V geodome requires 96 metres of rods, quite a number...
I was thinking of using Al or steel pipes Fi=10-15mm, pressed at the edges with some kind of jig build around hidraulic press, even to build single dome one has to organize things like for running production :-)

[bojan]

I think we have to wait for el ninja to develop in full..
Then the poly people will be more willing to accept unusual orders....

[astro_nutt]

Just a thought..watertanks being watertight..don't forget some extra ventilation around the floor area first..just to be safe..before working on the inside.

[Gargoyle_Steve]

Yeah nightstalker I know many people could build somethign for themselves, and have done so already, that ended up being way cheaper than this. I have neither the time nor inclination to get into a project that complex because (as I'm pretty sure my grade 10 woodwork teacher would say) "it would be a mess". :lol:

I used the 2.5 metre diameter $2k unit delivered as an example, I'd personally be using something smaller myself when the time comes, but I was making a more direct comparison size and price wise to the a 2.3 m Sirius dome, priced at $6k here in oz, making the water tank conversion a MUCH cheaper idea!

During my research a while ago I found the website for this company in the US: http://www.explora-dome.com - their dome sells for US$650. That's right, basic dome structure with slide open sky hatch for $650. Surely we can come up with something in this, the "Clever Country" that is a bit more realistically priced!

More great images here:
http://www.explora-dome.com/View_Explora-Dome_Pictures.cfm

As suggested by Miaplacidus I have already considered talking to existing water tank manufacturers re a possible partnership in dome making, but as Paul, Dennis, etc have already pointed out there is gold in water tank manufacture at present.

Interestingly the Exploradome / Polydome people started out as - yes, water tank manufacturers! It all uses the same kind of polyethylene rotomoulding process, and they now have close to 200 different products (http://www.polytankco.com/polydome.html)in their lineup.

Click on this link and scroll about 2/3 of the way down to read how the astro domes began after an amateur astronomer approached them with an idea:

http://www.pappasgrills.com/exploradome.aspx


I still think there's a great opportunity in here somewhere, and I'll continue to follow through on this idea in the future and see what I eventually come up with.

[JimmyH155]

I used a very cheap observatory. I bought a standard 7 ft x 5ft shed and didn't fix the roof on. I merely tied the roof down at each corner with a stout elastic luggage strap,to a strong peg in the ground, put 4 bits of wood on the walls to rest the roof on. For added peace of mind I put on top of the roof 4 large bricks.
With a rectangular shed I was able to put in shelves - how would you do that with a round tank??
Inside, all I did for the tripod was to cut 3 holes in the lawn (about 200mm dia and deep) and filled them with concrete. Just before it set, I plonked the tripod on top to make a little dent in each bit of concrete, and then when set, I aligned and levelled the scope and BINGO there was my fixed scope. For observing, it took me about 3 minutes to remove the bricks, and undo the elastic straps and lift the roof off. :D
Modifying a poly tank sounds very dodgy to me - you are going to destroy all the strength of the cylinder, it will become uncontrollably floppy and you will have to spend a fortune beefing it up - if at all possible.;)

[Gargoyle_Steve]

Jimmy good on you for making your own observatory! :thumbsup:

With respect to "destroying all the strength of the cylinder" I don't see that losing strength is a factor at all - the above mentioned example of a 2.5 metre tank is a >10,000 litre unit, it has VERY strong, thick, corrugated sides - by comparison some of the specific astro domes are made of exactly the same material, ie rotomoulded polyethylene, but are manufactured with much thinner walls :lol: I guess if they work when designed to only hold their own weight, then a water tank conversion will be more than sufficient for the task since it's designed to contain 10,000+ kg's of water.

As for shelving - well they manage to mount them in the round domes ok, I think I'd just cut curved shelves out of ply and put them on brackets - who says shelves have to be straight? :P

As Omaroo said up above he's already seen someone who's done it, so we already have verification that it's not only theoretically possible, but in fact quite doable! (Any chance of some pics Omaroo?)

I hope to add my own version to the observatory community at some stage in the future. If & when I finally have the room, and the need to do it, I'll post the pics and let you all know!

;)

[Garyh]

Why not use a zinculume tank? they are cheaper and empty they would have much stronger walls..
We have both at home and the metal tanks are much stronger as the curved corrigated iron makes for a strong wall..Add a 100mm concrete floor cut a door hole and cut of the sheet metal top and you are on your way..you can use this spare sheet metal as part of your dome or roof..

[xelasnave]

I originaly thought of a plastic tank "lid" to go on the rock observatory I have been building... for about 3 years now!!!!... it started as a pile of rock gathered from around the new cleared yard I had put in after the fires cleaned me out ...
With fire a worry I thought about the bottom of a steel tank. Once you think about it ..it becomes clear you dont need a dome.

I have not talked to the guy about it for a while but he is going to make a steel tank for me with only a few rungs (about of foot) ... that will sit on top of the 6 foot walls. It will need some internal support but he said maybe $500.

I have been hoping an old tank "appears" as things do as the botom of an old tank is more often intact.

However the roll off shed works very well so I am not in a rush with the stone observatory ... It is to house the yet to be built English Equatorial mount holding the 16 inch??? well at least the 12 inch.

But I would suggest any one thinking on these problems to consider a roll off shed.. it is cheap easy and efficient. The only sckill required is patience.

alex