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Old 27-06-2022, 15:44   #1
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How much support do poly tanks need?

I thought I'd have the tanks installed in one day but I live in fantasy.

I have some 10mm poly tanks but how much support do they need?

They are going in the settees against the curved hull. There's a gap of course.

There are suggestions of using foam. It would be nice to avoid it because of the mess and not being able to remove the tanks.

They don't sit well against the hull because of the curve. The largest face is against the settee, does that need supporting there?

Otherwise I'll epoxy some saddles to the hull and use webbing straps to keep them down.
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Old 27-06-2022, 19:09   #2
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Re: How much support do poly tanks need?

All PE tanks will eventually fail because of movement (and fatigue) and embrittlement. Any flexing speeds up the process. Support them accordingly.
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Old 27-06-2022, 19:53   #3
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Re: How much support do poly tanks need?

Push some plastic bags down between the hull and the tank and pour two pack polyurethane foam into the top of the bag. Do it in small batches and keep some weight on the top of the tank to stop the expanding foam from lifting the tank.
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Old 27-06-2022, 19:57   #4
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Re: How much support do poly tanks need?

The answer to your question is, it depends on the wall thickness. 10mm (3/8") tank walls are definitely thick enough to support the 8.333 lbs/gal that water and waste weigh with minimal support. Looking at you photo, the bottom and vertical side are already well supported...the sloped right side is only surface that needs any support and it doesn't need much...maybe 2 or 3 wood "slats"--one at each end and one in the middle should do it. It's unlikely to bounce, can't slide even an inch, so I wouldn't bother with straps unless you just want them.

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Old 27-06-2022, 22:43   #5
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Re: How much support do poly tanks need?

I had some insulation board for something else. I made a template for the tank. A kitchen knife and hot gluing different pieces together has made a snug fit.

I'm happy. It's easy removable and no mess if I ever have to remove that foam. Spray foam seems like such a short cut with a nightmare if it ever needs redoing.
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Old 28-06-2022, 07:16   #6
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Re: How much support do poly tanks need?

All I can say is WOW! I'd love to see how you've mapped out the plumbing runs and how you intend to install the hose fittings in the tank.

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Old 28-06-2022, 08:05   #7
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Re: How much support do poly tanks need?

I dont think they need any support per se, but need to be held so they dont move around. If that is what you are asking. I have water tanks of 500-1300 gallons unsupported on land that are less than half that thick.
Your wall thickness to capacity comparison is way beyond what my big tanks have. But I would probably like to see some support of a flat panel longer than maybe 2 ft max to prevent distortion etc.
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Old 28-06-2022, 16:39   #8
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Re: How much support do poly tanks need?

The fill hose comes from above with an air bleed too.

Otherwise it just drops under the sole with PEX tubing to the pressure pump. I have some valves to isolate both tanks but not sure if I'll bother.

I was thinking those big poly rainwater tanks don't have much support and sit outside in the weather for years. Yeah, they don't move and water doesn't slosh but they are pretty thin.
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Old 28-06-2022, 19:02   #9
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Re: How much support do poly tanks need?

Quote:
Originally Posted by WaldPinkler View Post
I was thinking those big poly rainwater tanks don't have much support and sit outside in the weather for years. Yeah, they don't move and water doesn't slosh but they are pretty thin.

If you read the instructions for them, they all require a uniform, flat, level floor to sit on.
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Old 29-06-2022, 02:15   #10
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Re: How much support do poly tanks need?

We have a 400 litre poly tank under our double bunk and I would say the base is the only place where there is 100% surface contact. The rest of the tank is just wedged and locked in place to stop it moving.
Speaking of big poly tanks, we have two 30,000 litre tanks next to our house. They are pretty thin and are 12 years old. The only time they failed was when we emptied one and I walked on top of it on a 35 degree day (95 Fahrenheit). The top caved down and I had to grab a jack, some timber and jump inside the tank to pop the top back into it's tepee shape.
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