Diving Tank 4

[CostalGuy]

hello all, this is my first post after checking this forum for help several times. I stink at coming up with names so I am stuck with the current one... I am doing a side project for a volunteer organization I belong to and the grand scheme of things is this: We have a 1100 gallon poly water storage tank (5'-4" diameter, 7' tall) and the idea is to modify the tank to put windows in it so outsiders can observe SCUBA divers inside. See the attached sketch for the concept idea, note that the tank size has gotten much smaller.

the plan is to install 3'x3' windows at between 13" and 4' down from the top of the tank. I may have overthought this problem but the total force I have on the window would be about 1,500#, Scaling things up for a safety factor has me analyzing the windows at 5 psi (double the pressure); the resulting hoop stress for a 1/4" thick tank is 160 psi. Polycarbonate has a tensile strength of 9,500 psi, so I am not worried about that.

I was anticipating fastening the glass with 2 rows of 1/4" ss fasteners at 3" o.c. staggered and was curious to see if I could estimate the block shear strength based on the thickness of the materials. Would that even be a concern? I feel like I am overlooking something.

The material sizes and loads all seem kind of small for the application but I am also only holding back worse case scenario of 250 psf

any sort of insight is appreciated as I don't want to spill potentially 500 gallons of water

 

[IRstuff]

I suggest that you revisit ALL your numbers, since the drawing does not match your narrative description, e.g., 5'-4" diameter 7' tall compared to 8' diameter 8' tall in the drawing.

Additionally, your window sizes also don't match, and the windows in the drawing occupy nearly 50% of the circumference, which seems like a lot.

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[IRstuff]

Even your volume estimate is suspect, based on the drawing; I get more like 2256 gal above the bottom sills of the windows

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[CostalGuy]

I understand the sizes are different, I had mentioned that in the first post. I am working on shop drawings now of the project idea so I have not had the chance to change the sketch. The concept is what I was introducing.

 

[CostalGuy]

here is an image of the actual tank, the blue is an outline of a 3'x3' window. Tank is 5'-4" in diameter, and 7' tall to the dome

 

[HTURKAK]

If i were , I would ;

- Consider 2 in ( 50 mm ) splice ..In this case Polycarbonate plate size would be ( 40 in X 40 in)

- the connection should be designed as slip critical , consider grinding (with sandpaper)) the faying surfaces to get better slip critical surfaces .

- apply polycarbonate glue . ( the glue essentially for sealing like gasket )

- drill holes and use ss fasteners together with flanges at both sides ( metal flanges square shape with interior size 3ftX3ft are necessary to prestress the faying surfaces )..

- hydrostatic test the tank for double pressure ..



my opinion

I cannot give you the formula for success, but I can give you the formula for failure..It is: Try to please everybody.

 

[dvd]

Musings -

[ul]
[li]Investigate plastics welders and incorporate stiffeners into the window framing.[/li]
[li]Cutting top off of tank will lose rigidity.[/li]
[li]How is tank going to be rigged and moved?[/li]
[li]Lose the square corners, consider round portholes and bolted flanges.[/li]
[/ul]

 

[LittleInch]

I suggest you forget this and start looking at under water cameras.

Your window will need to be curved to the same diameter otherwise you will have a world of pain sealing the base and also the sides.

Or just install some swimming pool portholes.

But most anything you buy will be designed for a flat surface so start to think about this.

Why not build a square tank?

Cutting up an tank will destroy its strength at the top and cutting holes in it won't do it any good either.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[FacEngrPE]

This search

https://duckduckgo.com/?t=lm&q=poly+tank+window&iax=images&ia=images

came up with several examples. Some of these examples show stiffeners and reinforcement integral to the tank around the window.
If this tank were being treated as either an API tank or a ASME vessel, any opening the size you propose must be reinforced to ensure the load can be carried around the window. It will likely cost less to order the tank with reinforcement built in than to set up to add the reinforcement needed.
If you decide to use a slip critical arrangement
[ul]
[li]Openings with square corners are crack starters even in a soft material like poly.[/li]
[li]If the top of the tank is cut off the increased flexibility will create undesirable bending around the relatively stiff window. If you order an open top tank, it may need a top edge stiffener to keep flexibility in check (one reason to order the tank with all necessary stiffeners and reinforcement).[/li]
[/ul]

 

[CostalGuy]

I appreciate the input, a lot of good ideas that I will incorporate; Analyzing as a slip critical connection is a good idea, roughening/cleaning the faying surfaces is a great idea as well as using appropriate epoxy. Fender washers will be a must too.

The stress concentrations at the square edge comes to mind, but to help mitigate that we can use a hole saw to round the corners so that there is not a stress concentration.

reinforcing the openings is also an idea that I had had as well. I was thinking once the hole is cut, that the edges can be reinforced with fiberglass lapped on either side of the tank.

I was anticipating reinforcing the top lip of the tank with either fiberglass and plywood (make a flange) or reinforcing that with a coping of steel or Azek.

To answer a few questions give some more background:
I belong to a volunteer underwater search and rescue group. The tank will be used for fund raising/promotion. The tank will be permenantly attached to an old trailer; the tank itself will have a steel platform to support it with drop columns/bearing plates so that the water weight bypasses the trailer and is a stand-alone structure. To access the tank, there will be a 60" tall stair platform with a ladder to get in and out of the tank as well. Because we are part of the first responders network, a tanker truck can be called to deliver water once the trailer is parked. Before leaving the fundraising event, the tank will be emptied, top secure, and then towed to the next location. The purpose of the windows is for the public to see into the tank; as good as go-pro's are, you lose the interaction aspect if it was just broadcast on a screen.


also, I was looking at a typical dunk tank and it seems like the window and the reinforcement is very small comparatively speaking. the water depth will be basically the same this is why I can't help but think that I am overthinking this

I have finished the first draft of the shop drawings so that the concept is much clearer

 

[LittleInch]

Something like this?

https://www.windowo.com/underwater-portholes

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[LittleInch]

Our you might be better off cutting the tank vertically in half and then bolt on two flat sides of clear material with something along the base, so basically a U shaped section.

Getting the clear elements made to an exact diameter plus the metal support frame will not be easy, cheap or straightforward.

Especially with all the moving around and filling and draining this thing will leak continuously unless you make it very rigid.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[LittleInch]

Our just get the largest polycarbonate tube you can buy, looks to be about 2m diam.

E.g

https://m.made-in-china.com/product...Large-Plastic-Fish-Tank-Oxygen-910307925.html

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EdStainless]

Compare the stiffness of the tank and the window.
Under stress the tank may move a lot more than your window, and the greatly intensifies the forces.
I would consider a series of smaller windows running down the side, they could be staggered so that the stresses don't align.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[BridgeSmith]

You should watch a few episodes of "Tanked", and pay close attention to how they design and construct their aquariums.

I'm curious what a diver could possibly do in a tank that small that would be interesting enough to watch.

 

[XR250]

This seems like a really bad idea. I like the underwater camera angle.
Be careful about having poor boundaries around a volunteer organization job.

 

[SwinnyGG]

You're way, way overthinking this.

Reinforce the top of the cut tank with rolled angle.

Cut a hole (round is best...) and bolt the window to the inside. You'll want a doubler between bolt head and window, and another one between tank wall and nut/washer. Seal with RTV on the window and tank wall, if you want to go crazy put a bead around the outside of the window (inside the tank) and fill the bolt holes prior to tightening down.

You're talking about 1 psi. This is not a pressure vessel and none of this requires hours of calculation.

 

[BridgeSmith]

Well, more like 3-4 psi, but your point is well taken, SwinnyGG. The hard part will be getting a window, be it glass or clear poly, that matches the curvature.

 

[SwinnyGG]

If you do the math it's actually 1.5 psi.

The panel needs to curved, no doubt.. but that's easy too. lay the tank on its side before cutting any holes in it or cutting the top off, and you have an exact buck for making curved poly. Heat it up, let it curve, it'll exactly match the tank radius.

 

[rb1957]

'cept if you want the window to be bigger than the hole (to put the window inside the tank).

you could make a net sized window (as big as the hole) then use splices to join to the container.

"Hoffen wir mal, dass alles gut geht !"
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