Howdy all!
Somehow I knew this would be a contentious thread!!
Just to clarify a few things...
My initial point of view was that the suggestion was "just so wrong"! I mean we get told repeatedly about having a deep pier, separating the pier from the observatory base, etc. And after all, I'm in IT, not civil engineering, so I just take the advice as given.
However the arguments in favour are fascinating, including one given privately.
I should clarify though, the water tank doesn't exist yet, neither does the house (or as astro-friends refer to it: the observatory with attached bedrooms!). So a trial is out of the question yet.
I have heard a number of very reasonable arguments against the proposal. From a purely hypothetical point of view, one wonders how one might address them.
Mass: When we put in a pier normally, we put a pier foundation that weighs about 1 metric tonne (1 cubic metre of concrete). I am guessing that any reasonable size concrete tank filled with water (or even without) is likely to weigh at least the same. So is there any inherently problematic issue?
Separation: Normally we would not walk on the pier foundation - it would be separated from the observatory foundations/floor. If the tank were surrounded by a frame, and the floor were suspended from the frame, it could be separated from the tank.
Strength: Several people have suggested that the roof of the tank needs to be thick enough or supported underneath the pier to avoid vibrations further.
Thermal Mass: If the tank was contained inside the observatory (via the above frame), would this then reduce the issue?
Like I said, I am not committed to this, but I have found it an interesting thought experiment.
I was then even more intrigued after watching two videos about the AEC piers:
If I followed this correctly, it would seem reasonable that imaging should be undertaken while well away form the scope (eg inside the house!), as any local movement is still likely to affect the scope. Not sure of the validity of the comments, but it doesn't seem unreasonable.
Anyway guys, thanks for the comments, and I am keen to hear others thoughts (pro or anti), especially where actual experiences can be related.