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Old 15-06-2021, 09:48   #1
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Converted Water-Diesel Tank Reversal

Hi everyone,

Hoping you are able to help,

We have recently brought a boat and sadly it was hidden that the previous owners converted the 100 Gallon Water Tank to be a secondary diesel tank (in addition to the initial 100G diesel tank). This has left us now without a water tank on board so desperately need to convert this space back to a water tank.

We know that it is not simply cleaning as the water will not be potable after so we are looking into other ideas to convert this space.

Our current thinking is to cut open the Stainless tank, clean out the diesel and then use it as simply a container for a Water Bladder. This is proving quite hard to find a bladder that fits well as our tank is angeled with the Bilge of the boat.

Does anyone have experience using Bladders in odd shape areas? Or are there any other solutions that could work easily for us?

The boat is a 37ft Tayana if this helps at all.

Appreciate your help.
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Old 15-06-2021, 16:07   #2
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Re: Converted Water-Diesel Tank Reversal

If itís a stainless tank and you remove all the hoses and can install a few stainless screw in plates, I canít see why it cannot be cleaned, then steam cleaned if you are still concerned. Access plates will permit tank cleaning companies to get at the entire tank. They have real high pressure and hot water.
Have a water testing company confirm the tank is ok and add a filter system if you are still concerned.
What is the reason you believe the tank cannot be cleaned. Not a do it yourself job, but the professionals can tell you if itís go or no go after inspection.
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Old 15-06-2021, 16:57   #3
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Re: Converted Water-Diesel Tank Reversal

Manate is correct, given good enough access to the interior, no reason it cannot be successfully cleaned. However, this sounds like a pretty old tank, so do a careful inspection for corrosion and potential leaks, especially at the welds. Otherwise, a bladder is one good approach (but I have nothing to offer in that regard.)

Alternatively, one could fiberglass the interior (with food-safe resins) if you don't want to R&R the tank itself.
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Old 15-06-2021, 17:36   #4
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Re: Converted Water-Diesel Tank Reversal

Instead of taking it out and steam cleaning it, and putting it back in, wouldn't it be cheaper simply to replace the tank?

And I am curious why on earth anyone with a 100 gal tank on a 37 foot boat would think they need another 100 gallons?? It's a sailboat, not a powerboat. And you need water to live!
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Old 15-06-2021, 17:58   #5
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Re: Converted Water-Diesel Tank Reversal

I am guessing no survey was done?
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Old 15-06-2021, 18:21   #6
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Re: Converted Water-Diesel Tank Reversal

If you decide to line the tank, ATL makes custom liners. The inside of the tank would need to be smooth.
ATL Aquifer and Aqua-Flex Collapsible Potable Drinking Water Bladders - NSF/ANSI 61 Rated
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Old 15-06-2021, 18:24   #7
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Re: Converted Water-Diesel Tank Reversal

I know this is not a direct answer to your question, but it may help you think about other options. My boat has 2 water tanks that can be separated manually with a valve. One of the tanks has a crack on the top. It's currently - and temporarily - fixed with flex tape and holds up well, but I will basically do the opposite of what you're planning on. I will take the top of the second tank off and put a diesel fuel bladder in it. I'm currently building a water maker so I won't need that second tank anymore and rather have more fuel. So instead of having 2 big water tanks I opt for one large water tank and a smaller intermediate water tank of 10-15 gallons which will be filled by the water maker and transferred to the the big tank if the quality is acceptable. So with a water maker and the assumption that all systems function properly and as planned, you will have an endless supply of water and store it in at least two separate tanks. You can also add a couple of separate water jugs on deck or a storage locker that you keep full with drinking water. If a water maker has ever crossed your mind, now would probably be a good time to rethink going back to less fuel and more water.

PS: I just read your post again to see that you have no water tank at all. I thought you had a second water tank of 100G which should be plenty for your boat. While my suggestion of a water maker may still apply, you will definitely need a solution to have a good amount of water with you, regardless of water maker or not. I hope you will find a suitable solution, and congratulations on your new boat.
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Old 15-06-2021, 19:05   #8
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Re: Converted Water-Diesel Tank Reversal

Quote:
Originally Posted by Manateeman View Post
Access plates will permit tank cleaning companies to get at the entire tank. They have real high pressure and hot water.
Sadly We are in Bocas Del Toro (Panama) where we purchased the vessel and relocated to. Infrastructure here is some what lacking, there are no companies here that would be able to do a proper professional clean as far as we know (We asked around a lot)

I attached pictures of the tank and its current access hatch, what we are scared of is that we read online that the stainless steel can soak in the diesel and cleaning it (DIY style) is not sufficient to turn to drinking water storage. We could be wrong though. Do you think this is something we could clean with a broom stick and some rags?


Quote:
Originally Posted by HopCar View Post
If you decide to line the tank, ATL makes custom liners.
Oh Thanks for the link, we will get in touch with them! Their bladders are super pricey for 100gal being $800-1200 USD, lets see if the a lining solution would be any different in price.


Quote:
Originally Posted by sanibel sailor View Post
I am guessing no survey was done?
Thats the worse part. We got and paid a SAMS certified surveyor to check out this vessel before buying. The water additional diesel tank was missed, the termites in galley and headliner were missed, the cracked chain plate, and even the rotten and wet bulk head were all missed and are now our projects to solve

Quote:
Originally Posted by MartinFr View Post
PS: I just read your post again to see that you have no water tank at all. I thought you had a second water tank of 100G which should be plenty for your boat. While my suggestion of a water maker may still apply, you will definitely need a solution to have a good amount of water with you, regardless of water maker or not. I hope you will find a suitable solution, and congratulations on your new boat.
Ha, yea right now we have a a few jerry cans on deck with water which we simply have to refill at local docks and marinas but this system isnt so sustainable long term. Once we solve the tankage issue for water, a water maker might come, of course budget pending by the end of our higher priority projects. Thanks for the advise still and good luck with your extra fuel tank addition.
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Old 15-06-2021, 19:20   #9
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Re: Converted Water-Diesel Tank Reversal

Broom stick and rags will not be sufficient, but there are chemicals that can clean oil, diesel and organic builtups, and a hot water splash can remove them afterwards.

Stainless steel can be cleaned.
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Old 15-06-2021, 19:29   #10
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Re: Converted Water-Diesel Tank Reversal

You don't need to change the hoses or the tank or put liners in it. Since it's a stainless tank you can just pump all the diesel out then fill it with a caustic soda solution (Caustic soda is often sold in hardware shops as drain cleaner) pump all the lines and fittings which have been exposed to diesel and leave it overnight. Pump out all the caustic solution and flush through everything a couple of times with clean water. Then fill the tank with potable water and do a taste test or if you're a particularly cautious type send a sample to get tested (send two, one which has been through the tank and one from the water source).

Caustic soda is very nasty on skin so take the precautions appropriate to handling caustic substances.
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Old 16-06-2021, 06:44   #11
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Re: Converted Water-Diesel Tank Reversal

I absolutely do not agree. Under no circumstances should you drink, use for cooking, or even shower in water unless itís been examined by a certified lab.
Caustic will clean a lot of surfaces but diesel is can contaminate very small spaces...pores in stainless welds. Professional tank cleaners use very high pressure hot water and super strong detergents. They might tell you they cannot do the job! Every possible crevice can contain diesel, for example, between the hoses and barb fittings, in pipe threads. The amounts are tiny, but caustic, detergents etc. are not going to get to them...that is why I said remove everything and get the opinion of a professional with experience and IF they say yes, get the water tested. Then...Iíd get a RO filter system...Even if it comes back clean, I would not use it for cooking or drinking for several months and then Iíd run the lab test again and see what was trapped by the filters.
Iíve had very poor results with bladder tanks. They are difficult to clean. No match for plastic or monel.
Could you please take more photos of the beams crossing the tank where they join the fore and aft members.
Diesel is nothing you want to fool with at any level in your drinking water. Iím not going to expand this post into the science of diesel contamination nor my professional credentials in food process engineering. If you cannot find people who truly know how to decontaminate your tank and test the water, do not try to do this yourself. Please. This is NOT something you can do yourself.
PM me if you need further advice.
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Old 16-06-2021, 07:39   #12
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Re: Converted Water-Diesel Tank Reversal

Re-reading this thread made me reconsider my opinion on cleaning the tank.

I agree with those recommending professional cleaning as one option. The probability of a "broomstick and rag" approach to cleaning is not likely to decontaminate corners, especially those at baffles and the top of the tank, unless the top were completely removed.

Given that IMHO it falls to a professional cleaning or tank replacement, as the effort to install a bladder or even coat the tank interior is more than the effort (and probably cost) to replace the tank.
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Old 16-06-2021, 11:07   #13
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Re: Converted Water-Diesel Tank Reversal

As far as bladders go there is likely an additional obstacle. Surely a 100 gallon tank of most configurations has at least one baffle. Getting rid of those and leaving a smooth surface for the bladder to rest against would be difficult with a steel tank.
Cost wise and piece of mind and a whole lot hassle - just replace it. I like Roto mounded tanks if possible but not aluminum or fiberglass. SS is ok but expensive to start with and heavier than poly and welds can be an issue over time.

I’ve been around and restoring boats for 50 yrs+ and sometimes we make emotional choices thinking we are saving money or time when the best thing to go is cut your losses early and just take it out and replace it.
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Old 16-06-2021, 11:20   #14
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Re: Converted Water-Diesel Tank Reversal

I would buy a purpose built potable water tank for marine use regardless of the material that your "converted" tank was made of.
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Old 16-06-2021, 11:21   #15
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Re: Converted Water-Diesel Tank Reversal

I would consider replacing the tank. Floor cross members would need to be cut but there are ways to put them back in. It is a big job. Seems like plastic would be fine for this. Until then consider 5 gallon water jugs?
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