Poll: Fuel Tank Material

What's the best material for new diesel fuel tanks? For cost purposes, let's assume installation costs are the same for all types and the Poly tanks cost $1500, Black Steel cost $2500, Aluminum tanks cost $4500 and Stainless Steel tanks cost $5500.

Let's assume vessels of common size here....in the 25-45 ft range. Tankage of 1000 gallons or less.

Are poly tanks as durable and safe as the metal tanks? Is there a reduction in resale value if poly is used instead of metal?

Which would you choose and why?

Are we assuming diesel fuel?

Although I have a Stainless steel tank in my uninspected charter boat, they aren't USCG approved for inspected vessels. So I would pass on that for resale considerations. Steel and Aluminum are both excellent. If it was a steel hulled vessel I would choose steel. For Fiberglass and Aluminum hulls, think the advantage goes to aluminum for corrosion resistance. Not real interested in poly as it seems a rarely used material in our boats for fuel. You left out fiberglass which I would put below aluminum and near steel.

Ted

Thanks, Ted. I added "diesel" to the post, but cannot find a way to edit the poll to include fiberglass. Hopefully, those who prefer fiberglass will choose other and explain via post.

I vote for steel, aluminum or FRP - whichever was built correctly and installed right. I have seen a build and install spec sheet for all three and miss a step or two and your tanks will not do well.

Then which care and maintenance steps did the owner miss that caused the tanks to fail. I have personally seen Al integral tanks, capacity 6000 gallons, fail due to owner miscues.

Not a simple question IMHO, but a good one Al. If I recall your steel tanks looked pretty good after 30+ years. Met a fellow this past summer whose steel tanks looked great as they enter their 5th decade.

The FRP Nordhavn tanks have been very good on their older vessels I've been told.

Last but not least, the jury has yet to weigh in on bio diesel and FRP.

Tom, my boat's original black steel tanks were replaced with Aluminum by the PO. In posting, I was assuming vessels of common size here....in the 25-45 ft range. Tankage of 1000 gallons or less. I'll add it to the original post.

We put new aluminum tanks in our last boat. The exterior was coated with epoxy before installation. They should last another 30 years? The tanks they replaced were iron and water collected underneath. Poor installation.

1-Fiberglass
2-Thick Poly
3-Aluminum
4-Steel
5-Stainless Steel

Fiberglass lasts forever.

Thick poly last forever and it's cheap. Plus you can see in it.

Aluminum lasts a very long time if it's mounted correctly and the welds are done right.

Steel is easy to weld and can last a very long time if painted and mounted properly.

I wouldn't waste my money on SS.

Actually I'd use any of the first 4 with no hesitation. Based on which one I could get the best price and build quality on.

PS - "forever" in this case = equals the life of the boat I would say.

Fiberglass - OEM

Stainless tanks are not a particularly good idea if one has other options. Their longevity is too dependent on too many variables to make them a smart choice. For a long time stainless was not a recommended material for fuel tanks by the ABYC although I understand they have amended this statement more recently.

Our boat's three original iron tanks were replaced the year before we bought the boat with five new stainless tanks. When we had the boat surveyed in Alameda, CA, the downside of stainless was brought to our attention by the surveyor. It was not an item he wrote up, but he wanted us to know the reasons why stainless was (at the time) not recommended.

However, he said, he knew of a lot of boats in his area that have stainless tanks and they had been trouble free for many years.

The primary issue is the grade of stainless that is used, and more important, the quality of the welds. Welding changes the properties of stainless and can expose it to early failure depending on the quality and technique of the welding.

Our fuel management process is designed to minimize the potential problems with stainless. We've had the boat for 17 years now and so far so good. How much longer the tanks will continue to behave is anyone's guess.

Were we to re-tank this (or any) boat we would go with an inert material such as fiberglass, plastic, or composite. Our other cruising boat has composite tanks and I would expect them to last as long as anyone would ever need them to last.

For diesel, I'm in the fiberglass camp as well, based on my experience with the Hatteras; but they were molded into the center of the hull, in the center of the boat, a great location IMO.

Next choice would be aluminum.

For a new build, FRP.

But I voted for steel. For a retrofit, which is likely what folks here would be considering, its hard to go past steel. My old ones lasted over 30 years, and would have lasted longer were it not for design/installation issues. It was a simple decision to replace with epoxy painted steel and correct the installation issues. They will last the rest of the boats life.

I would only go aluminum if I had a planing-capable boat where weight-saving merits the higher material cost. Poultice corrosion can be a big issue though.

I have no problem with thick poly other than its not as easy to fully utilize the space when near curved hull side or bottom. For a rectangular box, sure.

In all cases correct installation is a must, or problems are likely to emerge in a comparatively short time.

Insequent said:

I have no problem with thick poly other than its not as easy to fully utilize the space when near curved hull side or bottom. For a rectangular box, sure.

l

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You can have them custom made to almost whatever shape you want.

Capt.Bill11 said:

You can have them custom made to almost whatever shape you want.

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Curved sides, sloping bottom - I guess providing them with a ply template would get you there. And maybe even enough baffles too. But by then and with shipping will it be cheaper than steel?

Greetings,
Mr. FW. Did you get a cost estimate for FRP? FRP is OEM with us for fuel (850 gallons in three tanks with the waste (90gal) and water (550 gal) all in line just above the keel. Poly would be MY next choice IF, as mentioned you had the room for the extra thickness and loss of volume due to the rounded corners.

I have poly tanks on both my boats but the tanks are small. The problem I see with poly tanks is that they almost never have baffles. That isn't a problem for small tanks, but is a significant failing for larger tanks.

If I was building larger new tanks and money wasn't an issue I would spec monel tanks. Money will last forever unless it is poorly welded.

Capt.Bill11 said:

1-Fiberglass
2-Thick Poly
3-Aluminum
4-Steel
5-Stainless Steel

Fiberglass lasts forever.

Thick poly last forever and it's cheap. Plus you can see in it.

Aluminum lasts a very long time if it's mounted correctly and the welds are done right.

Steel is easy to weld and can last a very long time if painted and mounted properly.

I wouldn't waste my money on SS.

Actually I'd use any of the first 4 with no hesitation. Based on which one I could get the best price and build quality on.

PS - "forever" in this case = equals the life of the boat I would say.

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My order is much the same as Capt Bill's, except, my stops after the top three on the list. I see no reason to go to steel or stainless steel. Now, the construction and installation are very important on all three.

And, for the record, all we have is aluminum.

I'd vote plastic (poly) or FRP, with the concern re what might happen to FRP if ethanol mixed diesel ever became mandatory. So plastic (or poly as above), would get my vote. They can and are made to shape, and baffles can be also inserted. That or a number of smaller interconnected plastic tanks to achieve much the same baffling, but greater flexibility of volume management.

Are poly tanks as durable and safe as the metal tanks?

Yes. However, PE fuel tanks must be made of CROSS LINKED poly, which is not the same material used for water and waste tanks. Water and waste tanks are all LINEAR PE, which cannot be used for fuel holding. Polypropylene (PP), otoh, IS suitable for fuel holding and can be baffled. Triple M Plastics in Maine Triple M Plastic Products Inc is the only mfr I know of who makes custom PP tanks. They have an excellent reputation. They also make custom water and waste tanks.

TDunn,
Can you actually get monel these days? All kinds of things were made of monel back in the 50's including prop shafts and fasteners. Any idea how expensive it would be?

I don't think poly tanks can be easily made above a certain smallish size. I might be wrong there.

Highest quality alloy blend, thick material, properly welded, correctly installed - aluminum fuel tanks... For diesel or gasoline.

I recommend using Soltron additive to keep in-tank water a non issue for both fuel types.

Those are my # 1 choices for tank and additive! - Art

manyboats said:

TDunn,
Can you actually get monel these days? All kinds of things were made of monel back in the 50's including prop shafts and fasteners. Any idea how expensive it would be?

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Very, I suspect.
How about titanium? Was used in space craft, now they make bicycles of it. Watches too, noticeably lighter compared with steel equivalents.

Art said:

Highest quality alloy blend, thick material, properly welded, correctly installed - aluminum fuel tanks... For diesel or gasoline.

I recommend using Soltron additive to keep in-tank water a non issue for both fuel types.

Those are my # 1 choices for tank and additive! - Art

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Thanks, Art. Good info on the tank quality but I'd rather avoid this becoming an additive debate.

Another tank option would be a bladder inside a wooden box. At the other end of the scale from titanium, monel or whatever. Maybe a good option for an auxiliary tank.

I voted "other", which = Fiberglass.
Can easily be build in any size/shape you wish, will wipe down clean clean, and last you a life time. No fuss, no muss, fit, monitor, and more-or-less forget.

I went against the grain and voted for stainless, as this is what I used when replacing my tanks recently.


I'm surprised at the big price difference suggested, as the quotes I got were only slightly more than black steel. This was for stainless tanks almost double the thickness as the original stainless tanks.
My original tanks started to leak after over 30 years. The corrosion was external on the bottom where moisture collected under the tank. Internally they were like new. The replacement tanks were raised on mounts to allow air to circulate underneath, and gave slope down to a water drain point. I expect these will be good for a lifetime.


Just wondering why all the negative opinion on stainless.

AusCan said:

I went against the grain and voted for stainless, as this is what I used when replacing my tanks recently.


I'm surprised at the big price difference suggested, as the quotes I got were only slightly more than black steel. This was for stainless tanks almost double the thickness as the original stainless tanks.
My original tanks started to leak after over 30 years. The corrosion was external on the bottom where moisture collected under the tank. Internally they were like new. The replacement tanks were raised on mounts to allow air to circulate underneath, and gave slope down to a water drain point. I expect these will be good for a lifetime.
Just wondering why all the negative opinion on stainless.

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The fear of hidden crevice corrosion I think, Auscan. Incidentally, my tanks are stainless, having been converted from water to fuel when the old iron tanks got the usual pox, by the PO. They are still fine some 15 years later. (Bugger, Jinx you never heard that, ok?). I have installed food grade plastics for water, and am now a fan of those. Fuel grade plastic would be my choice for any replacement fuel situation now, (See Headmistress Peggy's post), but I'm sure your stainless will be just fine, as mine are also elevated and air circulates. One thing they did right way back in 1975.

I would vote for MONEL as a genuine fuel tank can easily be created.

With cost a factor the polly box for fuel would be OK for main tanks with a servicanble day tank to gravity feed the engine would be a second.

All the nonsense about fuel polishing and crap growing in the fuel need not exist if a genuine fuel tank design is used.

Hint , a fuel tank is not just a box filled with fuel.

Ski in NC said:

I don't think poly tanks can be easily made above a certain smallish size. I might be wrong there.

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"Marine Fuel and Water Tanks

No matter what the size, shape or design, we can custom fabricate to the exact specifications required for a variety of boats and watercraft."

From the site Peggy put up a link to.

Monel, a copper nickel alloy is alive and well. Sure it can be used for marine fuel tanks. But at around 6 times or more the fabricated cost per pound than steel, why do it? Especially with perfectly viable alternatives available.

Monel is great for Hxers, many of us have these cupro nickel units.