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geary126 05-08-2007 11:00 AM

Patching water tank?
So, on the Catalina, I have two tanks. One in the bow, near the sail locker, the other in the main cabin, on the starbord side, under the berth.

The second one was not installed, when I bought the boat. The PO lived aboard, needed space for crap.

I took tank #2 home to clean it, and noticed some hard caulk / silicone / something from a tube on one wall of the tank.

So, this might be a patch, it might be spillage from a sucky repair job above the tank, or perhaps a bird with a peculiar digestive problem got down below. Who knows?

Let's assume patch. My inclination is to remove the patch, inspect, and do something better / bulletproof. It's about 1" round blob, maybe 1.5"

Tank material is plastic, polystyrene (?), whatever the translucent material is that they make milk bottles out of these days.

My guess is that this is the one matereial epoxy won't stick to.

I know some of you will tell me to buy another one, but boat funds aren't what they once were.

Thanks, boyz.

ps. cleaning...guessing 1:10 bleach / water solution, let soak 24 hours...with brush inserted in via fitting?


huguley3 05-08-2007 11:22 AM

I am a total noob but your mention of sticking a brush in the tank reminded me of something. At a martial arts school I went to they had a water cooler with a 5 gallon plastic water container on top that they would refill rather than have a service replace. After awhile it would get pretty slimy on the inside and to clean it they would put ice cubes in it with soap and swirl it around. Worked very well and the ice could just be dumped out.

I can imagine the tank you are talking about is much bigger and would require some engineering to "swirl" it but most any problem involves trading off time and money and hey it could be fun. :)

rheaton 05-08-2007 11:28 AM

You might want to test the tank to see if it leaks. If you have access to a preasure tester, use this. If not, perhaps you could seal the fill hole, and hold the tank under water looking for bubbles from the suspected area. If no leak, then you have nothing to fix.

sailingdog 05-08-2007 12:15 PM

The tank is most likely polyethylene...not polystyrene... which is a lousy choice for potable water tanks. I believe epoxy will stick to it...but not very well.

Why are you assuming the tank needs to be patched... I wouldn't worry about that until you know the tank leaks.

geary126 05-08-2007 01:09 PM

okay. Good point. My To Do list is already daunting!

sailingdog 05-08-2007 01:22 PM

One way to patch polyethylene tanks that is a bit off the beaten path is the "candles" that they use to patch alpine ski bottoms. The bottom surface on alpine skis used to be a form of polyethylene or similar plastic... and we used to fill the gouges using a "candle" that was made of plastic and wax combined, and dripped the plastic into the surface and then filed the repair flat. I don't know if they still make the patching sticks, but if they do, they might be worth a shot.

TrueBlue 05-08-2007 01:31 PM

I removed a plastic water tank from a previous boat once and discovered blobs of caulking like substance adhered to the sides. This was apparently an attempt by the builder to dampen and isolate the tank from the hull and bulkhead it was attached to.

Is it possible that your "1" round blob" is not a patch, but an isolator of sorts, used to minimize vibration?

geary126 05-08-2007 02:15 PM

very clever, Mr. Bond...!

I'll have to look into this. Could be the answer. Makes sense: how could this stuff leak, without impact? This plastic looks pretty bulletproof, especially with water only.

Thanks, y'all. Will report back.

Open to cleaning suggestions.

Also: what to do with bow tank? remove and clean, or just clean in place?

Also (2) you guys use normal clear hose, or the reinforced stuff? Given that this is non thru hull related, seems like I could KISS.

hellosailor 05-08-2007 02:48 PM

Tom, I think the tanks are usually rotomolded polythene and not much bonds to that. There are some new epoxy sticks (i.e. like plumber's putty) that are targeted for PVC and other plastics but I don't think polythene is on the list, or that the epoxies are rated for drinking water use.

Traditionally you would buy a plastics welding kit, which includes a heat gun and plastic rods. Match the rod to your tank material and you literally weld in new plastic to fill the crack/hole and if you've done it right, you have it repaired.

But the simpler and cheaper route is probably to apply a patch or plug, which is a perfectly good permanent solution. If the hole is small, install a stainless or nylon bolt through it with a rubber or buna o-ring under the head, end of story. If there is a crack, not hole, drill a hole to relieve the stress at each end o fhte crack, the bolt a small stainless plate over it (plate inside the tank) with 4-6 bolts holding the stainless over a piece of gasket material. Again, end of story.

The tank CAN certainly be repaired, you just can't crazy glue it and walk away.<G>

One way to clean a tank that you can't reach inside of, is to use something like Polident and let it soak. Or, pour in coarse rock salt (deicing salt) or coarse koshering salt, and vigorously shake the tank. The salt crystals are just as sharp as an abrasive media--but you can water-wash all of them out afterwards.

"Makes sense: how could this stuff leak, without impact? " Bad casting. The folks who make rotomolded kayaks claim they have an incredibly large defect rate from bad castings, so they have to charge high prices for the ones that are cast properly. (Ahuh.<G>)

sailingdog 05-08-2007 03:00 PM


BTW, there are a few epoxy mixes that are rated for food area/potable water area use. Most are not though. Ice is also a good abrasive for cleaning out water tanks. :D

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