Flexible Fuel Tank

[cruiz9]

The good and the bad of fuel bladders,
I have 4 x 200 ltr tanks on my boat, i choose these as the fuel tanks compartments are designed to fit under the cockpit seats and to get them custommade in metal or poly was prohibitive, so the builder suggested to try bladders, i also fitted a bladder designed for black water waste.

So after 6 yrs and 1200 engine hours i can give a first hand opinion of them.

THE GOOD,
They are very strong being made of an inner and outer layer of thick welded plastic material ,not unlike Inflatable boat material.

Because they colapse as the fuel is used they contain virtually no air ,and so i have never had a problem with condensation, never had water in my pre filters .
They where cheaper than moulded poly Tanks ,$1200 v $350.
As long as they are contained in a snug and lined area they do not slop around to any noticable degree even though they have no built in baffles
Goes without saying but you will never have a corrosion problem.

THE BAD

They can leak, the reason they do this is the two layers are constricted together buy the inlet and outlet fittings which are just plastic Thru hull type fittings which regularly need tightning to compress the layers together at this point, and is part of your warranty , the trouble is if you over tighten which is very easy to do, you will stip the thread and fuel will start to leak in between the two layers causing the outer layer to harden and go brittle and crack, i have lost 2 tanks from this problem, fortunatley they were replaced under warranty and the new ones had heavier duty fitting on them.

They are slow to fill as they do not have breather pipes ,so you will get blow back if you use a standard bowser nozzle. Not a problem i have any more as i fill all my tanks from jerry cans thru a 5 micron filter funnel.

As mentioned above i had i bladder that was specifically for black water, i cannot recommend going this route as the material is porous to odour, not good if you need to mount it near living or sleeping areas

Hope this helps you to make a more informed decision
Richard

[Mike OReilly]

Thanks HopCar and Richard. Much appreciated. ATL seems to be a great resource for all kinds of tanks. Richard, do you have a company or brand name you share? I'm really getting interested in this idea.

[Delancey]

For what it worth, a few picks of large military versions in use and being tested as well as a ferry tank installed to extend the range of aircraft for deliveries.

[model 10]

[QUOTE=Mike OReilly;1502811]Whoa... Tell us more. I might pay if the quality is worth it. Are you saying the bladder options available to boaters are different, and poorer quality, than those available to aircraft owners? Why would that be?

Aircraft fuel bladders are very light for their size. They look to be hand made for the size of the compartment they are destined for, like the bay inside a wing. It seems like the reasons for the better quality would be obvious, it's the FAA. If we only had such oversight in the nautical world....
Their construction is from a stiff black rubberized fabric similar to the heaviest sail fabric, with lots of patches and grommets, nipples, plates etc. The fit is very good and there is probably no movement or chafe. Sometimes you may have wrinkles in the bottom that trap water but otherwise, pretty trouble free.
The manufacturers probably have molds for each model and location on plane, so you would need something like that for every boat to get the cost down to something you could afford. A wing tank for your neighbors little plane probably costs $2k new. A custom tank for you boat would cost a bunch.
There are ferry bladders that just sit on the floor but they are made differently.

[cruiz9]

Originally Posted by Mike OReilly

Thanks HopCar and Richard. Much appreciated. ATL seems to be a great resource for all kinds of tanks. Richard, do you have a company or brand name you share? I'm really getting interested in this idea.

Got mine from Turtlepac , Australia.

[hpeer]

Originally Posted by Mike OReilly

Can you tell me more about this Andy? I've got a decommissioned diesel tank and I'm trying to figure out what to do with it. I don't really need the fuel tankage (main tank is 80 gallons), but I've considered inserting a bladder just for the heck of it. My thought would also be to use it as storage and pump to the main tank when needed.

You've had a bad experience with these tanks?

BTW, I see this thread is pretty old. I hope the OP got the answer he wanted.

Hy decommissioned? If it was leaking there s some pretty decent tank sealant on the market.

[Mike OReilly]

Originally Posted by hpeer

Hy decommissioned? If it was leaking there s some pretty decent tank sealant on the market.

Do you have any suggestions for an old black iron tank Hpeer? How effective is this approach?

Our tank was decommissioned after failing a pressure test. This happened before we took ownership, so I don't actually know how badly, or even where it was leaking. Might be worth looking at the sealing idea. Thanks.

[socaldmax]

I've heard of a fairly thick tank sealant called Kreem, but it requires the tank to be rotated so that it flows to all corners of the tank. There is also another one called Red Kote, but it probably also requires tank rotation.

[hpeer]

I'm looking to seal a tank, for different reasons. But elsewhere on CF people put me on to Flame Master. I don't know if it up dork, but it sort a call at least.

Google flame master here on CF, It has been mentioned favorably a few times.

Flamemaster

[Terra Nova]

Originally Posted by danielgoldberg

...the idea of having many gallons of diesel in a bag that might leak makes me a touch nervous...

Don't metal tanks also give you a bit of advantage in the event of a fire?

Having a metal tank fabricated, to fit a particular space in your boat, is not a very big job. And, if the space is accessible, installation is not beyond the ability of many boat owners who are good with their hands. Where interior furnishings must be modified, to access available space, I've found a Fein oscillating multi tool to be indispensable.

Aluminum makes a good diesel tank. Inlet and outlet hose stubs can be welded on--no joints to leak. The best tech seems to be to completely encapsulate them in a couple layers of mat and resin, to resist external corrosion. And a small sump fitting with drain valve facilitates sampling and water and sediment removal. Clean-outs for each baffled section, same.