Water Tank Repair

[Rex Delay]

My water tanks are plastic and 30 yrs old. One has developed a split on the top. Stock tanks are rectangular and relatively affordable but smaller than existing, the tanks I have are curved to fit the shape of the hull. To have identical tanks or larger built is very expensive. Two options are available, custom built or bladder liner. Any input?

[hellosailor]

If you put a bladder inside your existing tank, it will be protected from chafe and work pretty well. If you put a bladder against the hull, you really want to put some smooth material in between them, because chafe and puncture are the main concerns, aside from properly securing the bladder.

Some of the tank makers have a very wide range of shapes and sizes that simply aren't listed by the chandleries, so it may pay to check directly with some manufacturers. Depending on access, it may also be feasible to have a gasket and plate through-bolted over the crack on the top of the tank. If the whole tank hasn't gone brittle, that should be repairable. (Metal or UHDPE plates inside and out, sandwiching a neoprene sheet on top of the tank, bolted together.)

[LuvToSail]

I recently installed 80 gallon bladder tanks into my old 120 gallon poly tanks that had both cracked and started leaking.

The bladder tanks selected where the same length as the old tanks (this is the most important dimension.)

I cut about a 1/3 of the top of the old poly tanks out (near the aft end) so I could slide the new bladders in. I drilled a hole in forward end of the tank and feed a string so the tank could be fished into position and pulled the tanks in.

The drain was positioned down and fill to top.

Adapters where purchased for fill and exit.

Enough slack and fair leading to avoid kinking the lines where planned out.

I replaced older lines that where red and looked like rudder fuel lines and where very gooey inside when removed (kind a brown slimy stuff that didn't look very appetizing.) I used proper clear reinforced potable water lines for replacement. I utimately decided on all new lines for water supply to the pump and right to the galley sink for cold water!

[Kefaa]

If you have the measurements - and can get a tank into an opening for it (or are willing to make one) - Ronco was able to fit mine exactly. Marine Tanks - Ronco Plastics

[Chief Engineer]

Call Sealand in Farmingdale New York

www.northeastsanitation.com/

Ask them about spin-welding

[barnakiel]

If you find a non-toxic sealant adhesive you may be able to put a large patch on top of the split.

b.

[GordMay]

There are a number of methods* of welding thermoplastics. I wouldn’t think spin-welding would apply to a water tank repair.

During spin welding, one part is held stationary in a holding fixture while second part is rotated against it under pressure at speeds up to 16,000 rpm. This resulting friction causes the joining surfaces to melt and fuse together, producing strong hermetic welds.

* ie:
1 Hot gas welding
2 Speed tip welding
3 Extrusion welding
4 Contact welding
5 Hot plate welding
6 High frequency welding
7 Injection welding
8 Ultrasonic welding
9 Friction welding - Spin welding
10 Laser welding
11 Solvent welding

[Pete7]

As Gord says there are a number of different ways. I watched Tec Tanks make a water tank at the Southampton Boat show last year. Wasn't overly complicated. Some sort of gun heated a plastic rod of stuff which was then laid into the join between the sides of the tank to sort of weld it in place. Wasn't paticularly high tech, they were doing it on a boat show stand.

Tek-Tanks - Custom made or standard fit water, waste and fuel tanks

Now, when I used to ski we used the PTFE stuff you get around the top of beer cans to hold them together to weld repairs to the sole of a ski melting it with a candle. A small gas flame and a strip of PTFE stuff (might be be right name) ought to seal it up nicely if you are careful. Afterall you have nothing to loose.

However, what caused the split in the first place? because if its movement you need to solve that first or it will fail again.

Pete

[Chief Engineer]

I mentioned spin welding as it is a way to custom fit your fittings not as a repair....sorry for the conphusion

[GordMay]

Originally Posted by Pete7

... A small gas flame and a strip of PTFE stuff (might be be right name) ...

PTFE is PolyTetraFluoroEthylene, commonly known as Teflon® (DuPont).

[hellosailor]

The ski repair sticks aren't PTFE, they are probably polythene or polyethylene. And while that might work on a water tank, it works best if the repair stick AND the cracked material are both heated enough to become fluid and truly fuse during the repair. Instead of futzing about with flaming plastic sticks, you can just buy a plastic heat welding gun, complete with an assortment of plastic repair sticks.

Even the infamous Harbor Freight sells them.

The rotomolded tanks always will have an advantage over the welded ones though, because when there are no seams, there are no seams that can open, fail, and leak.

[GordMay]

Originally Posted by hellosailor

The ski repair sticks aren't PTFE...
... The rotomolded tanks always will have an advantage over the welded ones though, because when there are no seams, there are no seams that can open, fail, and leak.

Indeed.