Recommended Size Tubing?

I am planning on building a dunk tank and I am not sure about what size
tubing I should use. The tank itself is going to be 4' x 4' x 4'(square).
This will hold 400 imperial gallons of water (4000lbs). I am planning on
building a frame and lining it with plywood. If I space the vertical tubing
at 12" c/c, what is the smallest size tubing I dare use?
Thanks for any advice,
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I stole this from William Beaty, Electrical Engineer / Physics explainer / K-6 science textbook content provider:
"pressure (psi) = depth(ft) * 15(psi-per-atm) / 33(ft-per-atm)
For example, if you go 66ft down under water, thats 30psi pressure."
(found by googling "water pressure depth")
So if the tank is only supporting the water inside it...
4' deep gives about 1.8 psi at the bottom (on the side). A 1' square at the bottom will have less than 12" x 12" x 1.8 psi of force trying to push it out. That comes to about 260 lb. that has to be resisted.
1/2" x 0.063" square tube can easily take this load if the welds are sound.
I am visualising a 4' cube. Vertical tube every 12"--so for each side, one in each corner and 3 in the middle. Since the water at the bottom is pushing out, you have to tie the vertical tubes on one side face together with the corresponding ones on the opposite face so the bottom doesn't spread. This could be done by welding all the verts to a 4' x 4' x 14 gauge (~0.075") sheet. These are the critical welds because they will be resisting the most force. If you want to make it stronger, you could reinforce the bottom by welding a band of tubing or 1/2" x 0.125" angle iron all the way around the bottom.
I would also band all the way around it horizontally at the top and every 16" of depth. 4 bands total (5 if you do the bottom, too).
Drill the tubing to accept 1/2" screws to engage your 3/4" plywood.
I would see about finding a 4' x 4' pallet to mount the thing on.
Jeff Dantzler
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Jeff Dantzler
Thanks Jeff, It sounds like it will work. Now to build it.
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