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Old 18-02-2016, 21:42   #1
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Fuel Tank Material

It all may be here somewhere, but my search and read technique did not find what I am seeking.

A friend want to replace "black iron" fuel tanks on his sail boat. Apparently they leak. MY limited knowledge and subject research has found information, lots of it, but few facts coupled with very little beyond strong opinion, even invective. For the moment I'd like to ignore costs of materials and fabrication (within reason) shapes, locations, and the like, but focus on strength, durability, and dependability in a tank carrying diesel. I do recognize a need for baffles, pickups, sensors, inspection, and the ability to clean it out.

Assuming a 45 gallon tank (actually two) of a more or less flatish rectangular box description, what material and ancillary things as above do you recommend.? The materials I can think of are aluminum, stainless (type) monel, black iron, or fiberglass (no!). Various plastics, as well as titanium, and bladders, have been mentioned to me in casual conversation, but I am not familiar with them when used as fuel tanks on sailboats. I know bout plastic fuel tanks on outboards. Thanks for your ideas, recommendations, and, most of all, experiences.

Brian, sometimes called "Old California"
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Old 18-02-2016, 22:34   #2
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Re: Fuel Tank Material

I have a 1986 boat and a 1979 boat and both have fiberglass diesel tanks and so far no leaking or problems I am aware of. So I am in-favor of fiberglass tanks, but like to hear what others have to say.

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Old 19-02-2016, 00:19   #3
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Re: Fuel Tank Material

Fiberglass tanks - There was good discussion on SSCA forum:
" selected special vinylester resins that are designed for chemical tanks, and the interior layer was resin-rich (resin plus cabosil). .... best material for resisting whatever they might decide to add to diesel in the future adoption of additives in diesel, such as in gasoline." (Epoxy does not hold up to these additives)

S. Steel - under impression stainless steel does not do well when deprived of oxygen.

Black Iron is fine as long as it is maintained well, i.e, water kept out, and inspection/clean-out ports installed, and used. Unfortunately, some boats had the fuel vent on the side of the hull, which allowed salt water to siphon, and led to corrosion. Many are coating the inside of black iron tanks with epoxies or urethane paints. It was recently explained to me by a knowledgeable welder that there is sulfur in diesel, and since tanks are vented there is moisture present (even without a siphoning problem), in combination a dilute sulfuric acid is formed, which degrades the metal over time. Nonetheless, 20 years is decent expected life.

Black iron with epoxy over the outside worked well for more than 20 years, and would still be viable at 30 if not for the vent issue. (So, with Black Iron, I'd coat inside & outside. A Trawler skipper in Santa Cruz is very happy with Master Series Silver paint as a coating and I'm told by distributor the fishing boats back east are also using it successfully in this application.)

Aluminum tanks are being used, however they cause pause for some given the corrosive marine environment.

Some "synthetic" tanks can still have a slight diesel smell penetrate. Moeller has many off-the-shelf shapes, however if they do not have exactly what you need, custom is expensive. Tek-Tanks is a manufacturer in UK, however they are no longer selling into US.

In theory bladders can be fitted, however for large tanks on a sail boat, there still seems to be unanswered questions, at least in my mind, about how that works out with a large heel undersail. If installing inside an existing metal tank, need to cut out baffles & grind everything smooth. Foam or other strips need to be installed about every 6" inches, and accommodation made for evacuating moisture from the bottom of the tank a bladder is inserted in (like a bilge pump). Bladder manufacturers usually want you to tell them exactly what to build. Found they were not able to advise a solution based on sketches of an existing tank. Maybe there are manufacturers that are better at that. A newer bladder solution sells the bladder, and parts, and leaves it to you to install connectors, hoses, etc. Not quite as turnkey as desired in a solution. Only a few years longevity.

May need to think about how a tank change will change weight distribution, and affect overall balance for sailing.

You've probably already found it, but there's a Union 36 and Union Polaris thread in here somewhere talking about tanks.

Please keep us posted as to your findings and determination, as equally interested.

Good Luck.
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Old 19-02-2016, 03:52   #4
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Re: Fuel Tank Material

ABYC H-33 specifies the requirements for diesel fuel systems on boats.

See also ➥
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Old 19-02-2016, 04:31   #5
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Re: Fuel Tank Material

I would say Monel ought to outlast the boat.
Look up Titanium welding, that alone I believe removes it as a possibility.
But, honestly, why wouldn't a "plastic" tank, last almost forever?
Bladders are fine, as long as you don't mind replacing them in ten years or so, I don't want bladders for many reasons including that they can get wrinkles that hold water, chafe is an issue and I've had too many problems with bladder tanks in airplanes.

Keeping a tank out of the water and water out of the tank is the issue I believe, my 1946 Cessna's original thin aluminum tanks are in nearly perfect condition, and they are 70 yrs old, but I don't think they have ever really had any water in them either.
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Old 19-02-2016, 04:53   #6
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Re: Fuel Tank Material

I have the original roto-molded plastic tanks in my 1979 boat. No Problems, no corrosion, less condensation.

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Old 19-02-2016, 05:32   #7
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Re: Fuel Tank Material

I think nearly all Automobiles have "plastic" fuel tanks now?
Good thing about plastic is it last nearly forever, bad thing about plastic is it last nearly forever

Majority of our hulls are plastic?

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