Replace Fuel Tank Advice

[bck73]

Yep I have the fuel sending hatch on top but its to small so I ended up cutting a hatch and cleaning out the tank then sealing it up

bck73
Mike

[HopCar]

If you're thinking of installing bladders in your existing tanks talk to the folks at Aero Tec Labs. They make all kinds of fuel bladders. Aero Tec Laboratories - Aero Tec Labs - Aerotech - ATL - Aerotec - AeroTech Labs, Fuel Cells_Cell, Bladders_Bladder, Bladder Tanks_Tank, Potable Water Bladders, Pillow Tanks_Tank_Containment, Portable Tanks_Tank, Liquid Storage, Collapsible Tanks_Tan

[colemj]

Originally Posted by Mike OReilly

Anyone have any experience with this solution?

I have been waiting for an answer to this. Everyone says to do it, but I don't know anyone who actually has.

For a tank of any decent size, it will have baffles and make putting in a bladder impossible. Another issue is management of fittings, chafing, etc while inside another tank. If the tank is so inaccessible as to not being able to get it out, then it will be extremely difficult to get a bladder into it.

I have put these bladders in boats before (open, extra spaces - not inside existing tanks), and they are stiff, have preformed shape and are not readily workable to pop into a hole and fit to a tank. They need to be tightly secured in all dimensions and free to expand in ways a fixed tank would not.

It is really only possible for small open tanks in accessible places - if at that.

I think it is one of those urban myth type things that everyone believes and propagates but hasn't experienced or spent any thought about the validity of the prospect.

Mark

[ovrmyhead]

Originally Posted by colemj

I have been waiting for an answer to this. Everyone says to do it, but I don't know anyone who actually has.

For a tank of any decent size, it will have baffles and make putting in a bladder impossible. Another issue is management of fittings, chafing, etc while inside another tank. If the tank is so inaccessible as to not being able to get it out, then it will be extremely difficult to get a bladder into it.

I have put these bladders in boats before (open, extra spaces - not inside existing tanks), and they are stiff, have preformed shape and are not readily workable to pop into a hole and fit to a tank. They need to be tightly secured in all dimensions and free to expand in ways a fixed tank would not.

It is really only possible for small open tanks in accessible places - if at that.

I think it is one of those urban myth type things that everyone believes and propagates but hasn't experienced or spent any thought about the validity of the prospect.

Mark

I 2nd this. Havent seen any approved for installation in hull, only topside tanks

[Mike OReilly]

Originally Posted by colemj

For a tank of any decent size, it will have baffles and make putting in a bladder impossible. Another issue is management of fittings, chafing, etc while inside another tank. If the tank is so inaccessible as to not being able to get it out, then it will be extremely difficult to get a bladder into it.

I have put these bladders in boats before (open, extra spaces - not inside existing tanks), and they are stiff, have preformed shape and are not readily workable to pop into a hole and fit to a tank. They need to be tightly secured in all dimensions and free to expand in ways a fixed tank would not.

Thanks Mark, much appreciate your thoughtful comments. I do have pretty good access to the top of the tank. The problem is that it is deep in the bilge. Removal would require taking out (destroying) parts of the cabin sole. Since I have a good 90 gallon tank, I'm not missing the extra diesel capacity.

Perhaps I'll just cut off the top and convert it to deep storage.

[colemj]

If you can access enough of the top, can you cut the top off, remove the baffles, and slide a smaller tank inside it?

But 90 gallons is a good capacity.

Mark

[Mike OReilly]

Originally Posted by colemj

If you can access enough of the top, can you cut the top off, remove the baffles, and slide a smaller tank inside it? But 90 gallons is a good capacity.

That's what I was thinking Mark. I expect to lose 1/3 to 1/2 the volume, but as you say, 90 gallons is pretty good. I've yet to have a problem with fuel capacity.

If it doesn't work, then I'll just use the space as storage.

[shorebird]

The original post did NOT specify diesel as the fuel, so any advice regarding grinding or cutting holes should be considered only for diesel, NOT for gasoline tanks, even if dead empty, and even if flushed with water.
MIC or "microbiologically induced corrosion" is a serious issue in tanks, and can corrode through steel or aluminum in short order. Typically, it affects mobile tanks less, since water in marine tanks is continually sloshed around inside the tank, inhibiting growth of micro-organisms and standing pockets of acidic secretions which is the direct cause of MIC. It is still essential to use fuel additives which inhibit these bugs from growing in your fuel, and promote dispersion of small amounts of water into the fuel. Keeping your tank full also helps prevent water in your tank.
It may be possible to have two or more smaller tanks installed in a confined space where one tank wouldn't fit, and join them by means of a union, known as |manifolding. We use this method frequently in generator tanks, but I don't know if the union joint would be suited to the frequent vibration and movement on board a boat.
If I were replacing the tanks on my own boat, I would opt for a steel tank, but would have the exterior galvanized before installation. For water tanks, if installation space was limited, I would not hesitate to use manifolded smaller tanks to create essentially, one larger tank.
BTW, I am a manufacturer of steel tanks ranging from 100 to 90,000 litres both for bulk storage and transport of fuel.

[Skip1990]

I am in the process of replacing my starboard 200 gallon diesel tank. As mentioned my boat is 22 years old so it lasted about 20 years. We had to cut up the old tank to get it out but we are designing the new tank so it will easily go back in. Cost of the tank is $1450. Total cost is going to be in the $5-6000 range. Therefore I would suggest waiting until the replacement is needed. It will begin to leak from a small hole so you will get warning before it gets too bad.

Good luck and keep your fingers crossed. You might never have to make the replacement.

[westsail42]

In response to the original poster, I would say:

Cut a hole in the tank as if you were to install an inspection port (like one of these: Fisheries - Product Detail)

Once the hole is cut, do an inspection and/or cleaning. If it needs replacement, deal with it. Otherwise install the port.

I would not necessarily assume the 20 year old aluminum tank is bad due to age.

A good external inspection of what you can may give some indication to the overall condition (corrosion along any welds?).

Also, is the tank painted or bare aluminum? A painted aluminum tank can last a long time over bare aluminum (depends on moisture, humidity and ventilation).

[DeepFrz]

Here is a blog of someone that did it.
Engine Room Refit Day 21 – We’re great; Tanks for asking | Sundowner sails again

[colemj]

They replaced with new tanks, not put a bladder in an old tank.

Mark

[DeepFrz]

They replaced with new tanks, not put a bladder in an old tank.

Oh yes, I forgot that was what you were interested in. Not something I would do myself so I guess I didn't pay much attention.

[Cheechako]

I would definitely find a way of checking them out. One of the few things I didnt replace on a boat once was two alum fuel tanks. The PO said they had been replaced once so I figured they must be good. Within a month of starting cruising I was getting diesel in the bilge. finally isolated the fwd tank as the culprit. I just pumped and abandoned that tank. Within less than a year the aft tank started leaking. arghhh. Subsequently it was found that the platform the tanks sat on had screws that were backing out over time... tiny holes started seeping. Another stainless tank (in the bilge but 10" above the bottom) went bad on another boat. It's a mess when it happens and these days it could be a very large fine. If you tanks are in the bilge I would def replace them. If under the setees etc, you ought to be able to assess them.

[Cinnamon Girl]

Thank you all for the thoughts. At this point, I believe we are going to go ahead with the inspection ports - with fingers crossed. Obviously, the difficult part of this is unhooking everything and then actually getting to the space. We will have to remove the batteries and possibly part of the cabin sole. The tank is tucked well into the starboard side and we cannot determine how it is attached or bonded. It would have been installed at the time the boat was built. Good thing we found is that the manufacturer of the tank is still in business and right here in town!