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Plastic Water tanks

Plastic Water tanks

by sirromcd » Fri Sep 05, 2008 7:27 pm

I have a Jeanneau 43 DS which has plastic water and fuel tanks. One of the water tanks has developed a small leak.
What is the best way to repair the tank? The plastic appears to be of similar material to plastic kayaks.
I am also looking at changing one of the water tanks to a diesel tank. Apart from changing the plumbing and making sure there is no residual water in the tank is there anything else that should be done?
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by RBEmerson » Fri Sep 05, 2008 10:08 pm

Two recommendations: 1) Replace the water tank, don't patch it. 2) Do not use a plastic (ex-)water tank for diesel fuel.

Ultimately, chasing the patching process will run out your patience. Replace the tank. You'll live longer, be nicer to live with, and not grind your teeth in frustration as yet another patch fails.

Most plastics used in making water tanks become dimensionally unstable (i.e., swell or contract) when soaked with diesel fuel. Tight hose or pipe fittings will no longer remain tight, etc.
Eat more moose, 17,000 wolves can't be wrong...
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by CaptCharles » Mon Sep 08, 2008 6:49 am

The good news is, that those tanks should be quite simple to remove and replace.
-Charles

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by osiris » Mon Sep 15, 2008 8:28 am

As a side note - - do not use any form of "bio-fuels" in plastic tanks including the plastic outboard motor gasoline portable tanks and plastic "jerry cans." BoatUS and others over the last year or so have found out that the tanks dissolve quickly when using bio-fuels and you end up with fuels spills/fuel draining into your boat. Just a little something the bio-fuel industry "forgot" to mention. The plastic tank industry is hard at work trying to formulate a new form of plastic that will be resistant to this problem.
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plastic water tanks

by s/v Active Transport » Mon Sep 15, 2008 4:42 pm

I had a NorSea 27 for about 12 years and it came with the original rotomolded polypro water tanks. The tanks were about 25 years old when I sold the boat and the only problem I ever had out of them was when I twisted one of the fittings, near the bottom of the tank, while trying to replace a stubborn hose clamp.

I asked a friend who had run a boat yard for years what I should do about it and his advice was as follows.

1. cut an access port in the top of the tank. Make a round hole the size of a standard plastic access port plate and flange so you can easily close up the tank when you are finished. Use food grade silicon caulk to bed the flange when mounting it on the tank.

2. Save the plug you take out when you cut the hole and cut some long slivers of the polypro material to use like solder in your repair.

3. Use a soldering gun to melt the area around the hole in the tank and push the end of one of your slivers of polypro material against the tip of the soldering gun, too. Melt the whole mess enough to get a good bond and you will probably have a workable fix. I got my leak fixed on the first try.


The repair I made in this way lasted 10 more years of extensive ocean sailing. The port made it possible to fill the tank quicker and to clean the inside of the tank, too.

I had to come up with a way to breath while doing the "welding". The tank was down inside a bunk so the fumes were not tolerable. I used my scuba gear including the mask to keep the fumes out of my eyes.

The man who taught me this trick was a very reputable surveyor and circumnavigator who had run a boat yard for years. He said this was a very common technique that they had used to repair tanks on new boats because the manufacturers were too cheap to let the yard replace tanks under warranty.

I think poly pro water tanks are a good choice if the tanks do not get too large. Polypro tanks are used to haul big tanks of insecticides around on pickup trucks so strength is not the problem. The major weakness of this material is that baffels can't be molded into these tanks so after 20 gallons or so they are not practical for water on a boat.

I have heard more stories about failed ss water tanks than I have heard about plastic tanks but I dont know how many tanks of each type there are in the world so I guess that bit of information is not too informative.

I should add that the tanks on my NorSea were foamed into place so they were well supported on the bottom and sides. The tops of the tanks were right under the plywood bunks.

I dont know about the appropriateness of this material for fuel tanks on a boat but I do know that some friends in Germany have a 1000 gallon polypro tank in the basement of their new home for heating oil and I cant imagine that the Germans are too casual about building safety standards. Again, the issue would be baffles and internal support for the tank walls.
John Lewis
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by svHyLyte » Tue Sep 16, 2008 8:41 am

Another simple alternative is to leave the plastic tanks in place, cut a large inspection port in the top, and use the tank as an enclosure for a bladder tank of roughly the same size that can be slipped in place through the inspection port. This alternative worked well for us with a cracked water tank in our old Cal 29.

s/v HyLyte :)
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by CaptCharles » Tue Sep 16, 2008 9:11 am

What about the new West System G-Flex Epoxy's? Arent they formulated for this task?
-Charles

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by Zanshin » Wed Sep 17, 2008 10:53 am

Which tank is the leaky one? If it is the s'board settee one then replacing it might be more work than using the inspection ports to fix it.
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by Kamaloha » Sat Oct 25, 2008 1:31 pm

I'll second John Lewis' suggestion for welding the rotomolded HDPE (High Density Polyethylene, not polypropylene) with a soldering iron. I've even repaired abraded jerry jugs successfully and they are a lot thinner. However it does require artistry; it is more difficult than soldering. The one suggestion I'd make is to practice on the pieces you cut out before going after the tank itself. It is very easy to make the tank walls thinner in the process. I found that using a low-wattage pencil iron with a homemade broad flat tip is best. Don't use a soldering gun as the heat varies too radically. Too hot and you drill holes rather than weld. Think of it kind of like spreading frosting on a cake. Practice, practice and you have a high chance of success. Note that milk jugs are also HDPE, and I usually use them as my repair material as they are thin and easier to melt into the surface of the item to be repaired.

You can't use epoxy on polyethylene. I use polyethylene containers to mix epoxy since it cleans out so well afterwards I can reuse the containers. :wink:

Diesel jerry jugs are made of the same stuff, so it should work perfectly well as a diesel tank if needed.
Charlie
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Re: Plastic Water tanks

by Zanshin » Thu Nov 10, 2011 9:31 am

I had a 43DS and the tanks look the same as on my subsequent boat, a Jeanneau 49DS. I contacted the manufacturer of the tanks (a French company, I can't recall the name at present) and they categorically stated that I could not use one of the water tanks for diesel fuel.
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Re: Plastic Water tanks

by RichH » Thu Mar 15, 2012 10:00 am

Joining/gluing/welding of HDPE and other low surface energy plastics has been a long term problem in the Chem Process Industries, etc.
Many adhesives manufacturers have addressed this problem in the past several years with 2 part acrylic adhesives.
Example: http://solutions.3m.com.au/3MContentRet ... =ImageFile
..... best used with a 'mechanical' fastening and overlayed with the 'acrylic' for sealing, etc. Make sure that the 'glue' is chemically compatible with the 'liquid' you want to contain in the HDPE tank, etc.

Welding of HDPE, etc. is an 'art' that usually requires lots of 'prior failures'.
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Re: Plastic Water tanks

by johnmartin348 » Thu Nov 15, 2012 1:37 am

welding is a best and proper option.. but it needs an experienced hand !
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Re: Plastic Water tanks

by FAST FRED » Mon Mar 14, 2016 12:52 pm

"Most plastics used in making water tanks become dimensionally unstable (i.e., swell or contract) when soaked with diesel fuel. Tight hose or pipe fittings will no longer remain tight, etc"

The plastic used for fuel tanks suffer from the same initial growth on filling.

A Plastic fuel tank should be put in place , filled with diesel for at least 48 hours , then fitted against motion.

I like the bladder idea as it could be removed and cleaned when becoming foul from bugs in the fuel.
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Re: Plastic Water tanks

by andredozzell » Tue Dec 26, 2017 2:29 am

I like the bladder idea too. Visions of the whole thing. It's all over the lifelines into the water. Right now I'm examining dedicated topping lift withing life.
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