Poly Tanks

[Richard Owen]

I saw the thread re: poly tanks and it reminded me of a question I had about the tanks on our boat. There are 5 water tanks of various sizes. In most cases they are in a section of the grid under the floor and thay have foam sprayed in around the sides, I think to prevent them from de-forming too much when full. One tank doesn't have this on one side, and when it's full, it looks like it might burst. The side of the tank is pushed out about 3 inches!!Is this normal, or is it a sign of future problems??ROwen

 

[Peggie Hall/HeadMistress]

Future problems...

Water and waste weigh 8.33 lbs/gallon...thin-walled tanks can't support it. It's the nature of water to try to spread out...but the walls on all but one side of that tank are "reinforced" by the foam, so it's following the line of least resistance--the weakest wall.No material can stretch without thinning...so as the bulged wall continues to bulge, it's getting thinner...and/or it's pulling the female fittings out of round. Be glad it's a water tank...'cuz sooner or later it's gonna leak--either around a fitting or it's gonna split. Since it IS just water, unless it's a large enough tank to flood your cabin sole, I'd just let it go till it does. 15, 25 or even more gallons of water your bilge won't sink your boat. And you've just illustrated far better than I can why we recommend a minimum wall thickness of 3/8"--on the smallest tanks...increasing in thickness with the size of the tank.

 

[Bruce]

reinforce if you can

Had the same problem with one of my tanks, and they are almost impossible to repair -- or find a good replacement for. After I finally went through the jigsaw puzzle of getting to the tank, I believe I could have reinforced it somewhat with strapping and possibly a 2x4 before it finally split at the upper corner where the side and top come together. If it was easy I guess (hope) Hunter would have done it right to begin with, but sure do recommend you find a way before it splits.By the way, nothing sticks to the poly tanks to repair it with after it breaks.