Poll: Fuel Tank Material

The large (40-50 gallon) plastic/poly tanks I've seen online don't seem to have good inspection/cleaning ports.

These guys suggest their product can be used in plastic tanks...do you think these would reduce structural strength or have issues with tanks swelling when full? Seabuilt - Access Plate Systems

This is off topic but was wondering at what tank capacity a baffle becomes desirable or needed?

I don't think a poly tank would be cheaper than a black steel tank unless you can use a small off the shelf rectangle. A custom shaped poly tank (175 gallons in our case) would probably cost more than stainless steel. When it comes time to replace the tanks on Walkabout I will probably use steel. The existing ones are 38 years old and do not leak. I guarantee the new ones will be made with much more care than the Taiwanese put into these. 38 years from now I will be 94 years old. Don't think I will care at that point.

READY2GO said:

I guarantee the new ones will be made with much more care than the Taiwanese put into these. 38 years from now I will be 94 years old. Don't think I will care at that point.

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How do you possibly guarantee that when you have no idea how much care they put in and when the existing ones have lasted 38 years?

BandB said:

How do you possibly guarantee that when you have no idea how much care they put in and when the existing ones have lasted 38 years?

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Having crawled through, under, over, around this boat sanding, painting, repairing, replacing, adjusting, redesigning, rebuilding almost every system I am very intimately acquainted with the Taiwanese forethought and quality control of TTs of that era.

The large (40-50 gallon) plastic/poly tanks I've seen online don't seem to have good inspection/cleaning ports.

Beckson Beckson Marine Inc.- Marine Hardware makes a full line of top quality retrofit inspection port kits. You'll find them under "deck plates."

Btw....when you visit their site, be sure to check out the "Rescue Friends" page.

If I were to replace tanks I would opt for steel. Epoxy painted on the outside, installed with some air space around them so they could dry, and I would put a slight angle on the installation so any water would settle into one corner. I would have a inspection port put above that low spot so I could get any water out if necessary.
I would also make them smaller...I don't need or want 360 gallons of fuel aboard.
If I could get a poly tank in the 75-100 gallon range I might choose poly.

Depends.....ask for a specific app and use...then I can be more specific.

AusCan said:

Just wondering why all the negative opinion on stainless.

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As it was explained to me, welding changes the properties of stainless at the weld. In essence it becomes "not so stainless anymore." So unless the welding is done exactly right, the risk of failure at the seams from corrosion increases and the risk gets greater the less correct the welding technique becomes.

Different grades of stainless have different degrees of resistance to corrosion. For example, stainless prop shafts are usually made with one of two grades of stainless, AQ-19 and AQ-22. As it was just explained to me by the yard our boat is currently in, both grades are identical in terms of strength. But AQ-22 is more resistant to corrosion than AQ-19. (It is also considerably more expensive.)

For boats that sit a lot AQ-22 is usually recommended because the shaft at the bearings and seals will be deprived of oxygen for long periods of time and so will be more susceptible to the formation of crevice corrosion. For boats that get more frequent use AQ-19 is the most typically used grade.

This is why it's important with boats with stainless shafts to "excercise" the shafts periodically, either by running the boat or turning the shafts over to exchange the water in the bearings and around the seals and thus expose the steel to oxygen. If crevice corrosion attacks a shaft the ultimate risk is the failure of the shaft, usually suddenly and at an inopportune time, if there is even such a thing as a shaft failure at an opportune time.

So the grade of stainless a fuel tank is made from will play a role in how resistant the tank will be to corrosion at the welds as well as the welding technique itself. We have the work order and charges for the manufacture of the stainless tanks that were put our boat in 1997. The cost of the tanks was $10,000. According to what we were told the grade of steel used is pretty resistant to corrosion. However, these properties are changed at the weld line. So how well the tanks in our boat will hold up over time remains to be seen.

In tracking down a very complex problem with our PNW cabin cruiser one of the shafts has been found to have slight crevice corrosion at a wear point. While the shop said the shaft can be cleaned up and that they have seen shafts with the small degree of crevice corrosion ours has continue on for many years trouble-free we have elected to replace the shaft.

A fuel tank can set up the exact condition you don't want with stainless--- the metal is deprived of oxygen for long periods of time. If there is any opportunity for corrosion to get a toehold along the weld lines, the tank is on its way to eventual failure.

We have designed our fuel management process to minimize this risk. What our process' contribution is to the longevity of our tanks is anyone's guess.

The water tanks in our boat are also stainless, but the turnover in a water tank is generally much higher than with a fuel tank. So the steel in the tank is getting "oxygenated" much more frequently. If our water tanks are original to the boat--- they may not be--- they are almost 43 years old now. So far there are no leaking problems that we are aware of.

"These guys suggest their product can be used in plastic tanks...do you think these would reduce structural strength or have issues with tanks swelling when full? Seabuilt - Access Plate Systems"

The size change (the tank grows after being filled with fuel) is simply part of a proper tank install.

Yes the boat gets the tank filled , then foamed or bolted in place.MFG dont like it because it adds labor to the out the door cost. The tank plate would then be added.

A bunch of plastic tanks would probably be great for a seasonal cruiser.

All but a small day tank could be drained , till the season begins.

Beckson sez,

A note about fuel tank mounting.
We do NOT recommend your using our deck plates for access directly into a fuel tank.
Through the deck above the tank? OK. But into the tank itself? No.
The diesel fuel would "eat up" the molded o-ring over time and would allow fuel to leak - a totally unacceptable situation. You are better off using an aluminum or stainless steel plate and a diesel-compatible gasket material, attaching this plate onto the tank with through-bolt fasteners.

Not sure if this is what you mean, but SeaBuilt has no O-ring. I had 2 SeaBuilt inspection plates professionally installed. They have nitrile (or similar) seals, not O rings.

Here's an image from their website:



Here's my installation:







Who the heck is Beckson????

Some more insight from an interesting article...

Stainless Steel​

My article “Tanks: Fuel, Water, and Holding” in the June ’01 issue of PMM included a discussion on fuel tank materials. At that time, stainless steel had not been approved by ABYC for use as a diesel fuel tank material, other than in 20-gallon cylindrical designs with domed heads (an impractical design at best). I’m pleased to report that the guidelines changed when the diesel fuel system standard was reissued in 2005. Now, stainless steel may be used for fuel tanks, provided the metal meets all other relevant ABYC requirements, essentially those outlined earlier for other metallic tank materials. Stainless steel, if used for fuel tank construction, must be of the 316L or 317L alloy variety and a minimum of 0.0747 inch thick.​

As most cruisers know, stainless steel is an exceptionally durable, long-lived material. Provided it’s properly designed and constructed and the correct stock material is used, a stainless fuel tank will serve you well. Stainless steel that is exposed to wet, oxygen-depleted environments will sometimes suffer from a phenomenon known as crevice corrosion. Much like aluminum, stainless steel must be exposed to a fresh supply of oxygen in order to remain corrosion free. If starved for oxygen while wet, pits or crevices will begin to appear on the metal’s surface. Once these materialize, the process accelerates as the pits form small galvanic cells. The key to enabling a stainless-steel tank to live a long life is keeping it dry (on the outside) and exposing it to circulating air.​

Finally, the “L” suffix after the alloy designation refers to its low carbon content, a prerequisite for any stainless steel that is to be welded. If stainless steel that is welded is not low carbon, weld decay (also called “carbide precipitation”) will occur: a narrow boundary on either side of the weld will be become susceptible to corrosion in much the same fashion as ordinary steel.​

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what_barnacles said:

Some more insight from an interesting article...

Diesel Fuel Tank Design | | PassageMaker​

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Good article. Jim a old salt retired commercial captain, now the owner of a sister RW58, and I had a discussion about replacing repair our 37 year old 400 gallon tanks. Our first choice would be multiple smaller tanks as we both have not filled either of our three 400 gal tanks. Plastic, poly would be our first choice as they are light, easier to handle, not have the concern mettle tanks would and last a long time.

Mild steel is the second, as they have lasted 37 year's and do not have the inherent concerns other metals do, and being old school. Also there are thousands of tanks older than ours still being used. The company I work for had 70+ year old tanks?

There is an old saying, a happy tank is a used tank.

I chose 3/16 aluminum for a replacement of the old steel tanks in the Grand Banks. After removing the old tanks, I built mock tanks from rigid foam to be sure that all would fit through through the doors and down into the bilge. Worked great. Aluminum was light enough to easily handle and with the help of a buddy, slipped right into place. They're smaller than the originals but with three, there's still enough capacity for me.

Fiberglass would worry me as the Gov is mandating bio trash be added to truck fuel, and the same tanker fills the marina as the truck stop. B-10 , now B 15.

When bio junk ( Ethanol) was forced into gasoline many boats had their fuel tank come apart inside.

The jets in a car are far larger than the diesel injectors , and fuel filters may pass particles 5x-10X larger than their rating.

the same tanker fills the marina as the truck stop.

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Well that's one low grade marina whatever it is. Every fuel dock I have ever used dispenses off-road diesel, with no ethanol whatsoever. Likewise it is easy to find non-ethanol gasoline in most major boating areas.

"Well that's one low grade marina whatever it is. Every fuel dock I have ever used dispenses off-road diesel, with no ethanol whatsoever." That may be correct today, but,,,,

Have you checked with the fuel delivery truck weather that red died "off road fuel" is not just home heating oil , run perhaps thru a filter to remove extra sludge and water?

When delivered to areas where less than full truck lots are the delivery norm , this is not uncommon.

Caviat Emptor!

The "best" fuel is usually at the commercial docks , but that 2 or 2 1/2 inch delivery nozzle deters some folks.

FF said:

The "best" fuel is usually at the commercial docks , but that 2 or 2 1/2 inch delivery nozzle deters some folks.

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The safest fuel remains at the highest volume marinas which definitely includes the commercial docks.

FF said:

Fiberglass would worry me as the Gov is mandating bio trash be added to truck fuel, and the same tanker fills the marina as the truck stop. B-10 , now B 15.

When bio junk ( Ethanol) was forced into gasoline many boats had their fuel tank come apart inside.

The jets in a car are far larger than the diesel injectors , and fuel filters may pass particles 5x-10X larger than their rating.

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caltexflanc said:

Well that's one low grade marina whatever it is. Every fuel dock I have ever used dispenses off-road diesel, with no ethanol whatsoever. Likewise it is easy to find non-ethanol gasoline in most major boating areas.

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FF said:

"Well that's one low grade marina whatever it is. Every fuel dock I have ever used dispenses off-road diesel, with no ethanol whatsoever." That may be correct today, but,,,,

Have you checked with the fuel delivery truck weather that red died "off road fuel" is not just home heating oil , run perhaps thru a filter to remove extra sludge and water?

When delivered to areas where less than full truck lots are the delivery norm , this is not uncommon.

Caviat Emptor!

The "best" fuel is usually at the commercial docks , but that 2 or 2 1/2 inch delivery nozzle deters some folks.

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BandB said:

The safest fuel remains at the highest volume marinas which definitely includes the commercial docks.

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Let's stick to fuel TANKS. Please feel free to debate the quality of various fuels in a dedicated thread.

"Let's stick to fuel TANKS. Please feel free to debate the quality of various fuels in a dedicated thread."

The quality of the build of the fuel tank will decide ,if when next filling they accidentally use a water hose , or you get really crap fuel ,, weather its merely a hassle or almost a disaster!

A bailing sump is the difference .

"Perfect" fuel every time , no problems.

Real world,, the tanks abilities should match the fuel being delivered.

I voted aluminum, as my 1981 vintage tanks are doing just fine.

But more importantly is the grade of any chosen material (if welded, the filler metal, too) and the quality of the fabrication (welding procedures).

Went with aircraft alloy alum alloy thirty second greater than required thickness pressure tested to spec. Used USCg snd ACBS info and application info for guidance.

I have stainless-steel fuel tanks. Nevertheless, I don't know which material is best, so did not vote.

I'm not a fan of aluminum, I've had two fail because of corrosion. Frp is the best for diesel. Cross link poly is my next choice. Monel would be the high end choice. One of the major advantages old Hatteras Yachts have frp tankage. I've never heard of a failure with diesel or water.

"Nevertheless, I don't know which material is best,"

Regardless of the material,,

the tank mounting and condition of the deck over the tank, and the filling setup are perhaps a bigger part of the equation.

FF said:

"Nevertheless, I don't know which material is best,"

Regardless of the material,,

the tank mounting and condition of the deck over the tank, and the filling setup are perhaps a bigger part of the equation.

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Fred's statement is Very Very True!

In addition to tank material choice... at least for metals, I don't know about plastics... keeping water out of tank insides is also paramount for longevity.

"keeping water out of tank insides is also paramount for longevity."

As water in small quantities is part of all clean diesel fuel this is impossible.

The best system I have seen has been posted a few times and consists of a sump which can be drained or even better bailed with a cup and strainer that is lifted up thru the fuel fill pipe.

Advantage here is the close fitting cup is all the water sees , so any bug waste is easily wiped as the water is removed.

Of course should you get a 1/2 tank of water , bailing may be slow but sure , and no electric or spare filters are required.

That's why I always say for a vessel a Fuel Tank is not simply a cheap box for fuel.

Strange, I have not seen any comment about fiberglass encased steel tanks like mine. These as near as I can determine were used for a time in newer Albins and Defevers.

Properly done it would seem the best of all choices, basically a tank within a tank. On the outside of the tanks all the problems with rusting from water leaks and improper mounting become non-issues. On the inside of the tanks, the steel could rust away and the tank remain leak free.

If properly glassed, I think this construction method could produce indestructible tanks but in the hands of the unskilled it would be the worst possible type of tank, Any moisture at all that gets between the tank and the glass dooms it to rapid failure and this was indeed the case with one of my day tanks which rotted out at a bottom fitting exposed to bilge water.

Again, I guess it all comes down to proper construction & installation.

What would be interesting to know out of all this tank discussion however would be how many have had a catastrophic failure resulting in filling the bilge with diesel. My worst fear is of this happening and my bilge pumps kicking in and pumping it all overboard into the marina. If not caught quickly, one might as well shoot themselves because no amount of insurance would cover the millions in clean up costs and frivolous law suits.

We have 2 ea 55 gallon and 2 ea 75 gallon aluminum tanks and one 150 gallon fiberglass . The aluminum tanks had just been installed before we purchased the boat . Not sure what was installed before . Having new tanks helped with the decision on which trawler to purchase when we were looking .

I don’t know. I’m at the point of replacing a Diesel fuel tank. anybody have an update to this last poll?