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Old 09-02-2015, 18:14   #1
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Diesel bladder tank

Hi everyone, I have noticed that my fiberglass integral 150gal fuel tank is leaking. It seems like diesel broke down the interior resin and fuel now slowly seeps thru the fiberglass mat. Can anyone give me some pointer as how to fix this? I was thinking about installing a bladder thank inside the old diesel tank. Is there a product like a resin that I can reply to the tank interior?

Thanks everyone




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Old 09-02-2015, 20:30   #2
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Re: Diesel bladder tank

I think your fiberglass integral tank can not be repaired. The resin is ruined.

Your idea of installing a bladder tank is a good one. I have seen them on other people's boats and they have worked well.

Drain your fiberglass integral tank and let the fiberglass dry out, line it completely with corrugated cardboard so the fiberglass doesn't abrade through the rubber, and install a bladder tank. The cardboard will probably have to be replaced every two years.
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Old 09-02-2015, 21:23   #3
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Re: Diesel bladder tank

No, please, no.... don't do bladder tanks!

I just spent a couple of weeks removing bladder tanks from our boat, and it was the most horrible job I have EVER done, and I've worked in some seriously horrible and messy professions in my life. And those were water tanks, not diesel, I cannot imagine how bad it would have been if they had contained diesel.

The problem is, the darn things have to fail eventually, then what do you do? You end up with rock hard plastic bags (and I mean really hard, I had to cut mine up in situ with a tree pruning saw) that have to be removed somehow. And the tiny little inspection ports that were on the top of my keel tanks were fine for getting the lovely soft flexible new tanks in, but not a hope in heck of getting the rigid slimy monsters out again 10 years later.

I have not yet had to replace the bladder tanks (surplus to our needs) but were I do so I would seriously consider poly tanks, either custom made to fit, or with luck, a production tank that was a reasonably good fit already.

If you want I will PM you some photos of the mess I removed, that might explain my apparent neurosis.

Matt
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Old 09-02-2015, 21:53   #4
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Re: Diesel bladder tank

I'm not commenting one way or the other on bladder tanks. But for the Poly ones, usually with a bit of catalog study, plus some 3-dimensional math, you can find one, or a combination of a couple, which fit "close enough".
You just need to do a bit of shelf construction, plus add some (sheet) closed cell foam, & a bit of 2-part pour foam, in order to fully support (and restrain) them. Plus of course, some well thought out, padded/chafe protected, hold down straps.

PS: How much area, & where, would you need to cut away so that you could retrofit new tanks into the old space(s)? And would said material to be cut away comprise much in terms of structural bits of the boat?
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Old 09-02-2015, 23:17   #5
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Re: Diesel bladder tank

Diesel bladder tanks have a long history in military use. I've also used ATL bladders for decades in motorsport applications with some very nasty fuels.

I don't see them much in recreational sail boats. Not sure why.

I certainly wouldn't line the old tank with cardboard. Not sure why that was recommended. Cardboard will just turn to mush.

Bladders usually have foam pieces installed to condense the vapour for gasoline applications. They also help a little with surge. Neither of these factors really apply to diesel in a boat.

I dont have any experience with bladders and salt water immersion.

Replacement of the plastic tank with a good quality plastic tank would be the most elegant solution.

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Old 09-02-2015, 23:33   #6
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Re: Diesel bladder tank

Quote:
Originally Posted by UNCIVILIZED View Post
.. plus add some (sheet) closed cell foam, & a bit of 2-part pour foam, in order to fully support (and restrain) them. Plus of course, some well thought out, padded/chafe protected, hold down straps.
Hey Uncivilized, I've been pondering the 2 part foam myself.

What's your thinking on using it to stabalise poly tanks in our keel? My only significant hesitation in finding some poly tanks to replace our horrid failed bladder tanks was wondering how I would secure them so that they did knock around and move. I worried that 2 part would become saturated over time and harbour more nasty smells so I was leaning towards timber inserts, which would be much more work and hard to get right.

Thoughts...?

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Old 10-02-2015, 11:14   #7
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Re: Diesel bladder tank

I've been doing a little, very preliminary, research on adding a diesel tank to my new/old boat. I looked in to the bladder tank idea and completely dropped it. You might get away with it as a temporary tank you could mount outside on deck if properly secured but I seem to remember that would be a bad idea too.

I have looked at poly tanks and will go that route if I do add. The big problem there is getting them inside the boat and then to where they will be installed. So measurements have to take into consideration hatch openings, etc.

But one thing I do know is that the tanks have to be strongly secured to the hull, preferably with tabbed in (glassed in) stringers. Heavy duty tabbed in. The stringers have to be stout as well and then the tanks have to be mechanically secured. Not sure what the references were to foam but if it meant to use it to secure the tank then that would be ludicrous. Foam degrades fairly rapidly. It does not handle repeated heavy, cyclic compressions and decompressions.

Any tank, of any type cannot rest on a flat surface, whether round, horizontal, vertical, whatever. There should be spacers between the tank and the mounting surface. If wedges are used they must be mechanically secured. If it were me, I would build a glass covered wood platform glassed it to the hull. And then use marine lumber or glassed in lumber to secure the tank from lateral and fore and aft movement along the bottom. And then add some kind of arrangement to keep the top and sides in place, much like you would for batteries (when installed correctly).

I am planning on it being a significant project when I get to it.
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Old 10-02-2015, 11:38   #8
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Re: Diesel bladder tank

I like the idea of putting one or two rigid plastic tanks in the current tank space. Keep in mind what your sailing intentions are. Many boats have way too much diesel capacity which only lets your diesel get real old as it never gets used up.


You could cut the top off the old tank for access. If doing so I would wash the tank interior with strong detergent... Joy is one of the best.
*Beware of using two part foam in a diesel saturated space... the diesel will eat up the foam into mush.
*There are better products than cardboard to line your old tank if you need to. The White or Blue packing foam comes in sheets (not Styrofoam, the Nylon like stuff) or there is poster material that looks like cardboard but is plastic... might work.
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Old 10-02-2015, 12:14   #9
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Re: Diesel bladder tank

The manufacturer of the bladder tank should be able to supply chafing material, if they can't perhaps pick another manufacturer. Chafing is the major thing that determines failure of aircraft fuel cells, and I can't imagine it would be that much different in a boat.
And be sure you have no wrinkle in the bottom of the cell when you install it too, but a bladder cell should last 20+ years, they do in aircraft anyway.
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Old 11-02-2015, 11:16   #10
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Re: Diesel bladder tank

I have used two Nauta flexible holding for twenty five years without a single problem. They can be used for fuel, water, or waste tanks.
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Old 11-02-2015, 11:47   #11
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Diesel bladder tank

After one of my 65 US gallon diesel tanks developed a leak I put a custom built bladder tank inside it. It was built by a manufacturer that makes fuel tanks for aircraft. Inside it is an open mesh material that acts as a baffle does in a solid tank. I lined the inside of the old tank with DryDeck tiles. Over 5 years so far and all is good.

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Old 11-02-2015, 15:23   #12
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Re: Diesel bladder tank

I'll definitely go with the bladder thank. These have been used in airplanes for decades the current thank has a very nice 18inch diameter access port so cleaning and lining should not be an issue.


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Old 11-02-2015, 16:49   #13
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Re: Diesel bladder tank

How I installed diesel bladder in my boat? Pumped bladder with air to become pilow shape, with mould relise i did cast GRP bottom half to become a "shelf", and instaled in the engine bay (it is hanged). Refill tube port is about 1 m above tank level to assure that tank will be refilled to its full capacity. How it works and benefits: when tank is full there are no kinks in the bladder walls and when empty the top of it just come down without sharp kinks and does not sucks humid air, tank does not "breathe" (daily occurance with rigid thanks trough breather), there is nill water condensation in my tank (it is major benefit, been there). Bladder was made by "Turtle Pack" in Brisbane with modified ports placement, and I have spare/replacement for "justin case". Six years and both (one installed and spare one) are as flexible as new.
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