Cracked Water Tank

[Garymadhatter]

My water tank on my 1980 O'Day 30 is cracked and needs to be replaced. It is impossible to remove without cutting it up. Has anyone had success with a flexible water tank? If so, do you recommend keeping the existing tank in place and placing the flexible tank inside? Any problems hooking up to the water line? Thanks

 

[Peggie Hall HeadMistress]

How many gallons does the tank hold? I'm asking because decent quality bladder tanks bigger than a few gallons can be a lot more expensive than a rigid plastic tank, but have only about a 10-15 yr lifespan.
No problem cutting up the existing tank to get it out...but you might want to look for another location for a new tank if you can't figure out how to improve access to install a new one--which doesn't have to be an "off the shelf" rectangular tank. Ronco Plastics Ronco Plastics marine Tanks (no relation to the VegoMatic Ronco) makes TOP quality thick-walled water and waste tanks for a very reasonable price and have more than 400 shapes and sizes, over 100 of which are non-rectangular, and they install fittings in the sizes and locations specified by the customer when they make the tank.

 

[Tally Ho]

I am not familiar with the O’Day 30. Where is the tank? I was able to remove the port-side tank on my O’Day 322 by removing 1 support bracket under my port settee.


This video has a little info on the water tank removal, installation.

Greg

 

[Panta Rei]

Cracked water tanks can be welded. It's very easy. Obviously, you must be able to get to it.
It's done using an iron similar to a soldering iron.https://www.eastwood.com/tpo-teo-pp...MIjKLf-rjJ2wIVwSFpCh30-ADyEAkYDiABEgLgt_D_BwE

 

[Peggie Hall HeadMistress]

Unlike filling gouges in the bottom of a snow ski, there's a little more to mending a cracked tank than just squirting some new PE (polyethylene) into the crack and smoothing it out with a warm clothes iron (I spent many a winter weekend evening doing that when I was on my ski club racing team...prob'ly the only time that ironing board and iron were ever used). First, whether the crack can be welded at all depends on the location. If it's in the top of the tank or on a vertical wall, the weight of the contents (water and sewage weigh 8.333 lbs/gallon) against the walls does its best to push the edges apart--and will succeed if not done correctly...and may anyway if the tank is a large one.
To do it right, it's necessary to melt at least 1/4", (up to 1/2" or more if it's a large tank) of the edges of the crack as you inject new melted PE into it so that they both run together to create a single mass that becomes a part of the rest of the tank wall. It doesn't appear that welder is the right type to do that...and I noticed that the list of plastics it's meant to work on does not include PE.

-- Peggie
"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein

 

[Panta Rei]

Let's not get everyone confused. Polyethylene tanks are welded all the time. It's the preferred way to fabricate custom PE tanks. Tank fabricators have expensive plastic welders that are fast and built to industrial standards. They are not needed for simple tank repair. The tool I recommended is ideal for tank repairs. I repaired the two 55 gallon water tanks on my O'day 39 using that tool. You can by PE or HDPE welding rods on many sites. Here is just one. https://www.amazon.com/Density-Polyethylene-Plastic-Welding-diameter/dp/B0007L7B5Y The site below shows the process well. The tool is slightly different than the one I used but they are both low cost and work the same.

Now back to Garymadhatter's original question. Yes, I have seen many collapsable blatters used for water tanks. I believe the trick is to locate the pickup at the bottom or keep all air out (no venting) so the water can be sucked out.

 

[Peggie Hall HeadMistress]

Polyethylene tanks are welded all the time. It's the preferred way to fabricate custom PE tanks.

Rotomolding is actually the preferred way to make PE tanks. Because welding them has to be done as I described, the best custom welded tank mfrs use PP instead of PE. If you successfully mended cracks in your tanks, the cracks would have to in a location where the weight of the contents (458 lbs in a 55 gal tank) puts no pressure on the walls ... OR the vertical walls are fully supported on all sides, creating resistance to the pressure of the weight inside the tank. Or you may have just proven the truth of the old saying, "there's a right way, a wrong way, and what some guy has gotten away with for years."

--Peggie
"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein