11.0 aluminum water tank

[Jtoben]

Everlastingly years ago I cut 4 access ports in the water tank of our 11.0a for clean out and inspection purposes. This past weekend I cleaned the tank and noticed about 6 deep pits in the bottom surface. The tank currently does not leak, but the depth of the pits relative to the thickness of the metal is of concern. I am researching products to coat the bottom and sides to stop the pitting from going further. We only use the water for dish shying and cleanup. We normally carry bottled water for cooking and drinking. We also have a PUR filter for the galley sink. So far I have been seeing epoxy products that should be painted on, and are rated for potable water tanks. Don't have any cost on it presently. I am wondering if anyone else has tried this fix to an old tank.

 

[Jtoben]

Sorry about the "everlastingly". I actually cut in the inspection ports about 10 years ago. Thanks to the iPad's auto word change....

 

[woodster]

not sure that coating will stop the corrosion.... only cover it up.... once its starts it seems to not stop

i just replaced mine with a new one that i built ...would have gone plastic but i didn't like paying freight on that one as it was as much as the tank cost...so it was back to aluminum one more time for about 25 more years......

 

[Mark Maulden]

I think I have a post here somewhere on my tanks. The quarter berth/setee tanks are easy to remove/replace. If they were made in FL, you can still roster by p/n. The sleep at night.....

 

[Mark Maulden]

Order by p/n. How do u turn auto correct off on an iPad? It's really a nuisance

 

[Jtoben]

I have been researching an epoxy coating that is very similar to a barrier coating. It is NSP 120 and has been tested for water potability. Very thick, would fill in the pits. It is just the bottom of the tank that is bad, but I would probably coat the seams as well. I have a bow tank. Friend with same boat had to have theirs pulled out by a marina yard, then replaced....$1500, mostly for labor to get the tank out. Yikes! If I can preserve the tank, it sure would be my first choice, and since it doesn't leak yet, it seems the simplest solution. Any thoughts on the epoxy? Another forum post said the US Navy is using high grade epoxy coatings over aluminum.

 

[justsomeguy]

Order by p/n. How do u turn auto correct off on an iPad? It's really a nuisance

Settings, General, Keyboard.

 

[BobM]

Its a ***** to get the tank out. I started mine a couple of years ago. That damned foam they used is a pain. I sent away for some info on a high solids epoxy used for coating municipal tanks. FC-22. They sell patch kits in caulking tubes which might do the trick depending on coverage. One headache is the baffles. Another owner did this job a while ago. May be in the kmowledgebase. I think he used brewcoat, but their smallest unit is 2 gallons for $220.

 

[BobM]

Here is a good thread.

http://forums.s2.sailboatowners.com/showthread.php?p=697953&highlight=Water tank coating

 

[Jtoben]

I've spoken to the technical expert at Progressive Polymer Coatings. The epoxy coating is a thick, barrier coat like substance and will fill in the pits and stop any further corrosion, it is essentially a barrier coat. It is rated for 10 years. Since I can access and clean my tank yearly, I plan to coat the bottom and seams and as far up the sides as I have product for. The sides, surprisingly are hardly corroded or pitted at all. Obviously the baffle could corrode and pit without me worrying about them, they have holes in them anyway, but they seem very clean and smooth. I will use a roller and brush to apply. Cheaper than a new tank, and I would hate to play with the structural stability that tank provides in the bow area by trying to fit in an alternative. We had some experience removing the holding tank years ago, bedded in that foam, and would like to avoid that headache in the bow area. Wish me luck.

 

[Mark Maulden]

Do u have some pix of the bow tank? That is our holding tank and I'm not sure how held in...

 

[Jtoben]

Mark, sorry it has taken me so long to reply. We do not have pics currently, I will take some in the spring of the bow tank...you are interested in how it is held down? Or the bedding compound? Or were you wondering about the interior epoxy coating?

 

[Mark Maulden]

Well sorta all of the above. If I open up my bunk boards, all I see is fiberglass. What's under it and where and how held in. Pic attached

 

[Jtoben]

Wow! To be honest, that looks like the top of our holding tank which, on our boat, was located under the port settee. It was custom formed to the shape of the hull, and was about 1/2" thick solid fiberglass. The fittings were bedded into it. It was held in place against the hull with a urethane bedding foam. If the bow is the location of your holding tank as you indicate, I suspect it is probably built as ours was. Our fittings had failed under the ownership of a previous owner, and odor had penetrated that foam bedding. The only way to remove the odor was to cut out and dispose of the original tank, then we completely removed all the urethane foam from the hull fiberglass. A long and careful process.

 

[RichH]

I have been researching an epoxy coating that is very similar to a barrier coating. It is NSP 120 and has been tested for water potability. Very thick, would fill in the pits. It is just the bottom of the tank that is bad, but I would probably coat the seams as well. I have a bow tank. Friend with same boat had to have theirs pulled out by a marina yard, then replaced....$1500, mostly for labor to get the tank out. Yikes! If I can preserve the tank, it sure would be my first choice, and since it doesn't leak yet, it seems the simplest solution. Any thoughts on the epoxy? Another forum post said the US Navy is using high grade epoxy coatings over aluminum.

Indeed NSP 120 is compatible for potable water, is used in various commercial applications.
Ive used it with limited results on a large aluminum tank.

1. You MUST provide lots of 'tooth' to the aluminum using 40-60 grit sanding discs, etc..
2. You really have to coat 100% the ENTIRE inside surface and no 'misses', because if there is any exposed metal surface and the water contains 'any' chlorine, aluminum chloride will eventually form 'behind' the coating and will 'push' the coating away from the metal surface causing even more aggressive lifting of the coating.

After 8-10 of service with that coating inplace, I replaced that 100 gallon coated aluminum tank with a stainless tank; but, if I were ever to do such a coating again, Id do a better 40grit sanding job, I'd probably add a layer of lightweight fiberglass cloth (for added strength) and with an extra coat of NSP-120 on top of the fiberglass to lessen the water intrusion through any 'holidays' in the coating. Inotherwords - building a tank in a tank, using the aluminum simply as a 'mold' for the new tank.
The coating has to be 110% perfect or it will eventually lift .... mine did after 8-10 years.

When I did originally coat the OEM tank, I had a 'leachables' test performed to validate the non-release (leachate) of 'organics' .... there were 'some' after the tank sat full of water over a long time. For the correction, I added a recirculating pump and small carbon packed filter to the tank, and simply 'stripped' the monomers, and other chemical fragments for several hours before using that water. A tank much less than 100 gallons would have a higher ratio of (low amine) epoxy contact surface to the volume of water contained with regards to 'some' leachables, probably more leachables than what I found.

NSP 120 is a seemingly good product, mix each component until its to the consistency of mayonaise before mixing the two components together and be sure to use the two pot method for mixing .... mix in one pot, remove that contents into a new container, then mix again ... so you get 'proper' and thorough mixing.

 

[woodster]

Wow! To be honest, that looks like the top of our holding tank which, on our boat, was located under the port settee. It was custom formed to the shape of the hull, and was about 1/2" thick solid fiberglass. The fittings were bedded into it. It was held in place against the hull with a urethane bedding foam. If the bow is the location of your holding tank as you indicate, I suspect it is probably built as ours was. Our fittings had failed under the ownership of a previous owner, and odor had penetrated that foam bedding. The only way to remove the odor was to cut out and dispose of the original tank, then we completely removed all the urethane foam from the hull fiberglass. A long and careful process.

i sorta think that is the holding tank as well why would you have two 1 &1/2 inch hoses coming out of the tank ...usually they have a 1& 1/2 inch fill hose...a 1/2 inch vent hose...and a 3/4 or 1/2 inch supply line ...just seems odd to me to have two 1& 1/2 inch lines

 

[Lorin Smith]

Epoxy coating inside a water tank? Aluminum is a poor choice for water tanks. No way around that. With the tank mounted and divided by baffles, a fellow needs to cut access holes into each segment. Then, working from a compromised posture, somehow prepare every square inch of every surface, most of it by feel since it can't be seen. Are we having fun yet? Then, after all that, set about applying the coating. An intoxicating experience!, Then, even if you achieve adequate coverage, your tank is left with plastic access ports mounted on an uneven surface never intended to accept them, prone to perpetual leakage. And you'll spend the next several years still not trusting the water enough to drink, while you are forever finding pieces of the deteriorating coating in any strainers of filters in your system. Been there, done that!! OR.... Bite the bullet, excavate the old tank out, along with whatever bedding compound surrounded it, and REPLACE IT with a new tank made of stainless steel. Custom made, multi faceted, fitted tanks with proper "clean out" ports included, can cost a lot less than the ordeal of fussing with a tank that ought never have been put in your boat in the first place.

 

[Mark Maulden]

I replaced alum with alum. Ordered the same p/ns which were still available. The original ones lasted 32 yrs so the new ones will most likely outlast me...

 

[Jtoben]

Rich, , thanks for that info. It is helpful. I will coat the entire interior this spring. No water in it last year, we weren't traveling and just used bottled, so no harm done.