Metal vs. Plastic Fuel Tanks

[B Tegge]

I pick door#3 fiberglass. My 1973 Irwin Has a Fiberglass fuel tank. Still original with no problems. Infanantly able to modify in place. I made a large inspection cover on the top. I can pull the cover and properly clean the tank anytime. Moved the tank vent to the center top. Fiberglass exhaust sections glass to the tank very well.

[wsmurdoch]

To the left is a 1988 Pacific Seacraft 34 0.090 aluminum fuel tank that developed a pinhole leak in 2018. It was repaired on a dock in the Bahamas with JB Weld putty, West System epoxy, and glass fiber cloth. To the right is its 2019 0.250 5052 aluminum replacement.


30 years is a long time. Aluminum lends itself to odd shapes. Aluminum is owner repairable.

Bill

[dkenny64]

well I'm with B Tegge, my 86 Irwin fiberglass tank is doing just fine..
fiberglass is user fixable and shapeable into any shape.
great for diesel..


not so great for gasoline/ethanol which tends to dissolve the resins compounds...making a mess..


fiberglass is also ok for most biodiesel blends..as is plastic.
copper/brass - watchout...if the biodiesel isn't washed well enough..it'll eat the copper/brass/bronze in no time...black iron..no problem..pain steel no problem..stainless no problem..


-dkenny64

[TommmD]

With water collecting over time in the tank, there's not many metal tanks that will hold up over 20 or 30 years. My present boat has a24 yr old HDPE tank, & with new fitting gaskets & hoses does n have a noticeable odor. Phillips head screws will not give you the clamping pressure you need to get good seals, paticularly on large flat gaskets like your guage. Change this over to socket heads, just don't torque too hard & strip the threaded inserts

[Singularity]

FRP or polyethylene for me. On it's best day metal is only as good as its welds (which, like surgery, are dependent on what the welder had for breakfast, where the moon is, if the wife is happy, etc). It's really hard to botch a FRP tank while I'd trust a rotomold over welds any day. From my perspective resale is higher with a rotomolded/FRP tank (if that matters).

There are zero UV concerns unless the tank will somehow be exposed to sunlight. Aren't we talking about below deck tanks?

The fire concerns are specious outright, but below are some anecdotes on FRP:

"ordinary polyester resin will usually withstand the 2.5 minute fire exposure, and a coat of fire-resistant paint [[or blanket cover]] on the outside is optional if you need more peace of mind."
"One [FRP] tank was inadvertently “tested” by a fire that devastated the facility where the tank was, but the tank itself survived virtually unscathed. Made with 1/8 inch skins of mat and woven roving on each side of a balsa core, the tank sustained charring damage to the outer skin, but the core and tank interior were not harmed. Resin was burned from the mat, while the charred woven roving seemed to act as a barrier which kept the core from burning, according to Gray. When asked about the affect of heat on the core, Gray noted that damage may have occurred, which means that had a foam material such as PVC been used instead, it might have deformed or worse, resulting in other problems or possibly a complete failure of the tank. Another report some years ago involved a similar blaze where an FRP tank containing gasoline in a boat survived and did not ignite, even when adjacent metal tanks in other boats exploded and burned."

https://www.practical-sailor.com/new...glasstanks.pdf

[thinwater]

Originally Posted by dkenny64

...fiberglass is user fixable and shapeable into any shape.
great for diesel..


not so great for gasoline/ethanol which tends to dissolve the resins compounds...making a mess....

Ethanol just takes a different resin. I built my first e10 tank for a boat in about 1990; I was in the refining industry, so I knew the resin and knew what was coming.



This is obvious; nearly all of the underground gasoline tanks in the country are fiberglass. No problem.

[CarinaPDX]

Shortly after the low-permeability standard (U.S.) came into force I tried to find a welded PE tank builder that would make me a new day tank; not a chance. Most websites had prominent warnings that their tanks were not to be used for fuel, others just said "no" on the phone. The rotomolded PE tanks are a different matter: my understanding is that they have an interior sealing layer to meet the standard - but of course they are mass-produced, not custom. Has this situation changed? If so I would like to know any custom manufacturers.

My old aluminum day tank corroded at the bottom where a small amount of water sat and wasn't drawn up through the draw tube. This is partly a design issue, but also a materials one. Perhaps this wasn't the best aluminum alloy to use - I don't know. I also have a stainless tank to supply my kerosene cooker (not the pressure tank) and it also corroded through on the bottom. In this case I suspect that the deck fill fitting wasn't sealing and salt water got in and just sat there in the space between the bottom and the outlet.

I had the bottom repaired on the kerosene tank (but am looking for a new diesel day tank). Plastic looks pretty good to me...

Greg

[thinwater]

Originally Posted by CarinaPDX

Shortly after the low-permeability standard (U.S.) came into force I tried to find a welded PE tank builder that would make me a new day tank; not a chance. Most websites had prominent warnings that their tanks were not to be used for fuel, others just said "no" on the phone. The rotomolded PE tanks are a different matter: my understanding is that they have an interior sealing layer to meet the standard - but of course they are mass-produced, not custom. Has this situation changed? If so I would like to know any custom manufacturers....
Greg

I think this is close to the heart of it. PE along was never really enough, for gasoline or diesel. The new tanks probably are.



My last poly tanks was older and permeated some smell, bu the builder was smart enough to put it in an above water line, vented compartment, like a propane locker, so no problem. Actually, that is the only way I would want a gas tank. Fortunately, that is easy on a multihull.

[a64pilot]

Polypropylene Diesel fuel tanks are fine.
http://triplemplastics.us/#&panel1-1

[Singularity]

Originally Posted by CarinaPDX

...The rotomolded PE tanks are a different matter: my understanding is that they have an interior sealing layer to meet the standard - but of course they are mass-produced, not custom. Has this situation changed? If so I would like to know any custom manufacturers....

As a data point I contacted Moeller (PE rotomold manufacturer) about making a couple larger perfectly rectangular tanks. I don't recall the guesstimate number for tooling alone but it was in the many thousands of dollar range (really based on their time/effort/headache factor, not per se the size of my tanks).

For smaller tanks I would build them myself with vinyl ester and fiberglass. If you have experience with fiberglass you know how easy it is; if you don't have experience then building little boxes is an excellent way to learn FRP skills that you can use elsewhere some day (if you have a FRP boat). Fraction of the cost of a metal tank.

[wtmf]

i want to thank everyone for all the imput. i am going to go small and change out like regular maintenance. all i need to do is set up the changeable pick up line.

[wsmurdoch]

In post #32 the wall thickness of the new tank should be 0.125 not 0.250.

Bill

[zeehag]

i replaced my plastic fuel tank which constantly grew gook to a custom stainless steel tank with which i am most happy. it has the weight needed in my boats belly and it holds more than the pos plastic one i ditched.
i willnot use a plastic tank again.
i had thought of fg tank, but.......
and ss is easily found and welders are many here. some even have skillz.

[Singularity]

Originally Posted by zeehag

i replaced my plastic fuel tank which constantly grew...

1. How often would you need to add fuel from usage?
2. How often would you sail?
3. What is your fuel polishing practice?
4. Any idea what type of plastic material that the tank was made of?

My impression, perhaps wrong, is that gook is most problematic in boats that don't move much (allowing formation of sizeable glycalaces making harder to kill/remove, even with biocides), low fuel turnover situations (allowing the critters to multiply instead of sending them through a flame somewhere), lack of water removal (allowing the presence of the substrate (water) needed for biologic growth).

FWIW metal tanks are more associated with water contamination issues than rubber tanks in petrol aircraft, theory being that water more readily condenses on the metal than the composite (water vapor entering through the vent). Insofar as diesel attracts water more than petrol, and many tanks sit in a cool bilge, I'd assume that plastic relatively superior from the condensation standpoint.

In any event, with regular polishing (starting from day 1) I don't see how biologics are a problem, but I can see how plastic tanks are harder to clean if neglected (relatively speaking).

[zeehag]

Originally Posted by Singularity

1. How often would you need to add fuel from usage?
2. How often would you sail?
3. What is your fuel polishing practice?
4. Any idea what type of plastic material that the tank was made of?

My impression, perhaps wrong, is that gook is most problematic in boats that don't move much (allowing formation of sizeable glycalaces making harder to kill/remove, even with biocides), low fuel turnover situations (allowing the critters to multiply instead of sending them through a flame somewhere), lack of water removal (allowing the presence of the substrate (water) needed for biologic growth).

FWIW metal tanks are more associated with water contamination issues than rubber tanks in petrol aircraft, theory being that water more readily condenses on the metal than the composite (water vapor entering through the vent). Insofar as diesel attracts water more than petrol, and many tanks sit in a cool bilge, I'd assume that plastic relatively superior from the condensation standpoint.

In any event, with regular polishing (starting from day 1) I don't see how biologics are a problem, but I can see how plastic tanks are harder to clean if neglected (relatively speaking).

HAHAHAHAHA i was constantly underway. the plastic tank was pos. we not repeating bs issues.
we have stainless beauty .
condensation?? in tropics, not much. measured and monitored and racor is real.
theory and reality are different situations.
i am in reality.

ps...when water temps and air temps are same, there is no condensation issue.