Sculpture Flotation Device

[whitts_r1]

Hello all,

Upon stumbling the forum during research I noticed some very helpful posts regarding calculation of buoyancy etc.

This is my first post, to introduce myself I am an engineering student with a large project on my hands and looking for sources of information.

I have been given the task of designing a device that will allow a sculpture to float in a pond of 5m depth. The sculpture has to maintain a 5-10mm distance from water level at all times leaving only the sculpture visible and the device fully submerged! (4-5" WATER LEVEL DEVIATION THROUGHOUT YEAR) meaning sculpture will be moving up&down.

The sculpture is of 485kg. The idea is to place the sculpture on framework incl. floats which will keep the sculpture afloat, by "counteracting" the weight of the structure against the upward force created by the floats (buoyancy).

where am I going with this? Well... I hope that with your knowledge of flotation/buoyancy calculations etc. I could be pointed in the right direction of information that would help me find out how I can make this work!!!

I appreciate that this is a boat design forum so if i have come to the total wrong place forgive me.

Many thanks in advance,
Paul.

Just some pics to maybe make more sense of this post!

(wood sculpture, grey = framework/structure, Yellow = floats, concrete base to sit on pond floor)

[Mr Efficiency]

That would be the sculpture, and only 5-10mm of that black tube above water level ? It is always raining in Ireland, they tell me, so a shower of rain wetting the sculpture will probably submerge it to the point where the sculpture is kissing the water, at which point it's bouyancy will kick in and stop it sinking. Seems like a very fine balance, the bouyancy in that tube is such a small fraction of the total.

[whitts_r1]

I have taken rainfall into account via rainfall records in the area which it will be situated. The material (irish oak) has also been studied and found to be not porous but I accept your reasoning.

The black tube is merely support/fixing @ center of gravity of sculpture. Yellow tanks are buoyancy. If the volume of tanks can be calculated with respect to the weight of the sculpture/framework unit, it will prevent from submerging. In addition, once at a constant distance from water level, the 4-5" water level deviation will become irrelevant as the height will be self corrected via buoyancy.

I hope I am explaining OK!

[Mr Efficiency]

OK, to clarify, what is touching the bottom of the pond ? I assume if it is all floating, it is anchored in some way, maybe via a short chain ? If the water level drops and some of the chain settles on the bottom it will cause the thing to rise slightly from water level ? The way I see it, it is depending on that thin tube to regulate height, via its bouyancy. Even rainwater beading on the sculpture will alter that.

[whitts_r1]

The base (bottom square) sought to be concrete will act as an anchor.

The centre column allows the whole top unit (consisting of sculpture, frame, buoy tanks) to move in the vertical direction via the sleeve. This unit is the moving part of the device. IT will move with water level. whilst the column&base will be anchored as one.

[Mr Efficiency]

Alright, but it still depends on that thin tube to regulate height, and needless to say any tendency of the sleeve to stick or jam will over-ride that. Wind pressure wouldn't help that. Growth of algae etc as well !

[whitts_r1]

All these factors have been looked at.

sleve sticking/jamming - brush mech. that will form barrier to prevent blockage etc. of debris of general type from that enviornment.

Wind is inevitable as sculpture cannot be modified and Ireland is windy! The device will be free to rotate thus allowing wind to create path of least resistance.

Algae is not an issue as pond wardens will carry out maintenance. be it clearing/cleaning build up of debris/algae!

...now back to the more important issue! lol

[whitts_r1]

very basic image to clear confusion.

[Mr Efficiency]

Seems pretty simple to me, just add/subtract more/less ballast till it floats where you want it. Of course, if anything under or above water absorbs water, all bets are off. Then someone has to go for a swim and adjust the ballast. You are almost trying to make a submergerged object float in mid-water, which is practically impossible, and as for timber that doesn't absorb water at all, that too is unlikely, you will need a masterful sealing job. Oh, and I forgot the bird crap will alter the weight, damn it !

[Submarine Tom]

You're going to need a pressure switch (and all the complications that go along with it) if you want it to maintain a certain depth in water that fluctuates in level. It would be a whole lot easier to fix the level of the water and then, simply fix the sculpture. A simple float switch and an overflow would fix your water level. Bolting down the sculpture at the correct height is easy.

If this is purely academic, then have at 'er. A worm gear comes to mind controlled by either a pressure switch or a float switch providing feedback on the height above water. Or use water sensors on the support shaft.

Perhaps a small, two way air pump could vary the air volume in the yellow box (open on the bottom).

Some kind of feedback loop that constantly monitors and adjusts it's depth in water.

Simpler the better...

-Tom

[whitts_r1]

The floats were going to be tanks designed to be a specific volume, calculated. What your saying is to have almost adjustable floats? this just adds to maintenance and more things going wring IMO.

As for the Irish Oak, I am going on my own research?
"Irish Oak wood in its natural form of "heartwood" is a dense fibrous material that will not degrade rapidly, nor become waterlogged. Irish Oak can support twenty years without any degradation, it is impermeable and therefore cannot benefit from additional treatment such as paints and varnishes, such treatments prevent the wood from breathing leading to more alterations being required over time, thus reducing its overall lifetime."

Bird crap is the least of my worries!

[whitts_r1]

Originally Posted by Submarine Tom

You're going to need a pressure switch (and all the complications that go along with it) if you want it to maintain a certain depth in water that fluctuates in level. It would be a whole lot easier to fix the level of the water and then, simply fix the sculpture. A simple float switch and an overflow would fix your water level. Bolting down the sculpture at the correct height is easy.

-Tom

quite true Tom but, overflow is ok for when water level is too high. what about when water level drops below average, then the fixture will be seen. This pond has no stream/water source running into it.

[Mr Efficiency]

It will not need to be anywhere near waterlogged to affect this very fine balance you have designed into the system. If your timber is "impermeable" then it won't be doing any breathing ! Good luck, but get ready to go for a swim when things go out of whack !

[whitts_r1]

Originally Posted by Mr Efficiency

It will not need to be anywhere near waterlogged to affect this very fine balance you have designed into the system. If your timber is "impermeable" then it won't be doing any breathing ! Good luck, but get ready to go for a swim when things go out of whack !

Thanks for the help.

[Submarine Tom]

Originally Posted by whitts_r1

quite true Tom but, overflow is ok for when water level is too high. what about when water level drops below average, then the fixture will be seen. This pond has no stream/water source running into it.

Then you'd need to plumb a supply line to it for the float switch to open and top up the pond.

Is this going to be real life or an academic exercise?

-Tom