Marine Fuel Tanks - PLastic Vs Aluminium - The Pros and Cons Debate

Marine Fuel Tanks - Plastic Vs Aluminum

This isn't a thought that crosses every boaters mind, and unless you hold on to your boat for a long period of time, are rebuilding a boat, or got a boat with a bad tank, you probably won't ever read this article.  For those that do indeed find themselves in that smaller crowd, I hope to shed some light on this situation.  

There are 4 main materials that are used for marine fuels tanks; polyethylene, aluminum, fiberglass, and stainless steel, of which the latter two are not as common so I am directing this article to polyethylene marine fuel tanks and aluminum marine fuel tanks.   In addition, this article is intended for standard gasoline permanent mounted boat fuel tanks and not for diesel fuel. 

Since I am not an expert in metal or types of plastic, I am basing this article more on the known pros and cons of marine plastic tanks and marine aluminum tanks. Again, I am no expert on this, and much of this information comes from talking to many "experts" in the industry, as well as some research.  From my research, the following are my beliefs on the subject.  If anyone has any "cited" information to contradict my opinions, please chime in via the comments below this article. When I say plastic I am using the term loosely, as most tanks are made with some sort of cross-linked high density Polyethylene resin, or better known as HDPE.

Pros and cons of Aluminum and Plastic Marine Fuel Tanks. 

Plastic Poly Marine Fuel Tank:

PROS

1) A major advantage, and one that persuades me right from the get-go is that tanks made from this material aren’t susceptible to corrosion. I believe the tanks are made from HDPE (High Density Polyethylene). 

2) Plastic tanks, if properly made will outlast aluminum marine tanks.  

3) Plastic marine fuel tanks cost less than aluminum marine tanks.  

4) According to many experts, plastic tanks are “incredibly durable” and much more reliable than aluminum tanks for gasoline. Diesel fuel may be another story.  

5) Being a non metallic composite, plastic fuel tanks won't introduce galvanic action to other components on your boat. 

6) Polyethylene marine fuel tanks are not affected by ethanol. 

7) Polyethylene fuel tanks have stronger seams than aluminum.  I'm not say that plastic is stronger than aluminum, but for the tensile strength of each when compared to it's own counterpart, the aluminum seam would be weaker.  

CONS

1) To the best of my knowledge, most plastic tanks don't have baffles inside the tank to limit the swashing of fuel and undue stress on the tank walls.  

2) I've heard that plastic tanks release vapors and after a period of time your boat begins to smell of fuel.  Personally, I've never encountered this with a plastic tank, and when I do smell fuel on a boat I suspect it's coming from another source.  All boat smell of fuel regardless of the tank, so even though I have this listed under cons, I don't believe it is a con.  

3) Limited selection due to most plastic tanks being roto spun in a mold, which makes custom plastic tanks expensive.  There are a few companies with a wide selection for the popular boats, but if you have a not so popular boat and need a plastic tank, well it may be a tough choice. 

Aluminum Marine Fuel Tank:

PROS

1) A correctly mounted aluminum marine fuel tank of high quality material, and  under ideal conditions should outlast the boat.  Some say they last 25-30 years, but I think they may go even longer as I've seen them past that mark and still in good shape.  I've also seen some in the 15 year range that looked to be 50 years old due to crevice corrosion as noted in the con below. 

2) Aluminum marine fuel tanks often have baffles in them to stabilize the fuel from swashing around excessively. 

3) Aluminum tanks are custom made, so getting one to match your boats design is a snap. A custom marine aluminum fuel tank can take advantage of extra space and allow for more fuel capacity.

4) Aluminum fuel tanks are stronger and resist punctures better than plastic.  Aluminum tends to dent and withstands more punishment. On a rebuttal side, I really don't see how a properly secured tank would be at risk, but during install this could be of concern.   

CONS

1) One of the biggest issues in aluminum marine fuel tanks are from builders foaming in the tanks.  Aluminum tanks do not like moisture over prolonged periods, and the foam against the tank enables major corrosion to occur.  The constant jarring of the boat eventually creates a seem between the tank and foam, which allows any moisture, whether from deck water running in or from simple condensation to do its damage.  A properly mounted aluminum will have good airflow around all surface areas, thus allowing it to dry.  Studies show that aluminum marine tanks are structurally sound for 10 years in most cases, and beyond that they begin to weaken and should be replaced.  

2) Buying an aluminum marine fuel tank of quality is easier said then done.  I'm sure you've seen stainless steel on a 40 year old boat that still looks new with no upkeep, yet the stainless on many of today's boats will rust out in a year or less.  This is simply due to the quality of the alloys.  Aluminum comes in different mixtures, and a lower grade alloy will not give you the 30 plus years.   The only real difference I see in the aluminum marine tanks on the market today are the thickness being offered.  The main protection in aluminum is the natural oxide on the surface of the aluminum.  A simple scratch removes this coating an opens the door to corrosion. 

3) The new ethanol fuel, as we all know by now attracts water.  As mentioned earlier, constant water in contact with aluminum will corrode the alloy, and is doing so with aluminum tanks.  Despite what you may have heard regarding aluminum marine fuel tanks having a protective coating inside is not true.  The protective coating is the actual oxide itself, and this gets destroyed as soon as the massive amount of heat takes hold from the welding of the seems.

4) Constant pressure and jarring of the boat puts a lot of stress on the aluminum welded seams, which are more apt to fractures.  I've never had a plastic seam on a decent product fracture unless it was dried out from sun damage, which won't be the case in the below deck fuel tanks .  On the flip side, my push pull platform has fractured at 2 of the 4 deck braces around the welds.

5) Due to Ethanol's action of attracting water, aluminum marine fuel tanks can and most often do create galvanic reactions throughout your boat. Zinc can be placed on the tank for exterior protection, but this does no good for the interior, thus leading to problems extending beyond just your tank, as well as corrosion attacking the welded seams from the inside out. 

6) Aluminum does not take well to alloys that are not of the same.  A simple loose bolt, screw, nut or any other metal object that were to fall on the tank and continue contact would eventually corrode that area.  Loose washers or other items seem to always find their way to the tank area.  In fact, as you may know we are doing a 225 Aquasport Osprey boat rebuild, and upon pulling the deck off we found several washers and screws that had been laying on the tank for many years, as evident by the fossil imprints they left behind. I have decided to go with Moeller, as they have a great reputation and also had the design that I needed.  Check the link above and follow the build.      

Conclusion of Aluminum Vs Plastic Marine Fuel Tanks:

Basing the conclusion on the winner between the pros and cons above really isn't fair, as there are many factors in determining the clear cut winner, such as the install being done correctly, airflow in the hull design, dry docked or wet slip, boat usage, maintenance, and many more.

I have a 55 gallon aluminum marine tank in my 1993 21' Hewes Light Tackle flats boat and after inspection it still looks new!  I have no idea what the inside looks like other than a very narrow look through the sending hole, which looked absolutely fine.  My tank is not foamed in so that gives it a fighting chance.  I know Hewes used all the best material available, as nothing on that boat has ever rusted that came originally on it.  The tank is not sitting on a wood bottom, and the support rails are angled to allow full drainage.  The entire tank has plenty of breathing room, and there are open air pathways that keep the air moving.  I have seen no foreign metal in contact with the tank, have put a meter on it and observed no current flow, so I am comfortable in saying that this tank should last the life of the boat.  

The example above is a good case scenario, however, with the introduction of Ethanol, there's no telling how long my aluminum tank will hold up.  I have always been a fan of aluminum, as it's stronger, and as far as metal goes, I feel it is the best alloy for marine use hands down.  But, since the introduction of ethanol, my favoritism is beginning to shift to plastic for marine fuel tanks. Plastic seems to be the winner by way technicality, as ethanol may be aluminum's Kryptonite.

 Allen Applegarth of FloridaInshoreAngler.com      

Comments 

 
0 #1 Riley
I couldn't agree with this article more. Well said FIA. I have had to many issues with metal tanks and I'm done. Nice looking tank you put in your rebuild there guys. Did you have that custom made or is it off the shelf? Sorry to post over here but I didn't see anything on the rebuild page to post.
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FIA REPLY:

It was an off the shelf tank, as a custom plastic tank would cost about 10k. Our tank was only 1/2 inch smaller end to end, but the capacity was the same somehow. Thanks for the comment.

Allen
 
 
+2 #2 Pete
Plastic for me. You nailed it FIA. I did go with metal however b/c I couldn't find the correct size plastic tank for my boat. Each has good point, but I think plastic takes the lead just as you have pointed out.
 
 
+1 #3 Poonman
I do a lot of rough water fishing and just feel more comfortable with metal having the baffles inside. I am able to get to my tank fairly easy so it's not that big of deal other than the cost if the metal goes bad. Either or I think is fine.
 
 
+2 #4 Hal Thomasson
The galvanized tanks in my 72 pacemaker have the lead peeling off on the inside of the tanks and after 40 years they need replacing. I'm leaning towards plastic, but the baffle issue has me holding back. Origional tanks are round so i"m going rectangle for more volume. Moeller has several plastic tanks in the 112 to 115 gallon range. still can't resolve the baffle issue. If anyone has these tanks installed in their boats please let me know if the baffle issue is a legitimate concern. Thanks
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FIA REPLY

Hi Hal,
I certainly see your concern, especially having multiple tanks. My new tank is roughly the same size as you are looking at, but my tanks sits low in the boat and I padded all sides out to 1/2 inch from the tank. Being that the center of gravity is so low, and the tank is surrounded by structure and padding, I don't foresee any issues with the boat being controlled by fuel movement.

Having 600 pounds or less sitting so low on a 6000 plus pound boat should not cause any noticeable movement in the boat overall. Being that the tank is narrow, side to side roll is my last concern due to very little distance to build momentum. The longer travel from end to end may produce more effects, but I doubt it will show any noticeable difference in bow to stern movement.

They do make a foam that you put into the tank aftermarket for this purpose, but I've never used it so I know nothing about it.

Also, the tank we removed was a Moeller, and nearly 18 years old and it was not secured as well as what we did for the new one, and yet it was still sitting in the original lock down position with no signs of wear from movement of the actual tank.

I would look at the placement of the tanks in relation to the center of gravity, the enclosures in which the tanks will rest, and possibly the aftermarket foam.

Please keep us updated on your decision and findings. Best of luck.

Allen
 
 
0 #5 Lenny
Great tanks. I installed one about 10 years ago and not a single problem. Someone commented about smelling fumes, no fumes in my boat unless i spill.
 
 
+1 #6 Rolando
1997 hewesLt20 I need a gas tank do you the size and how much is it thanks waiting for your reply rolando

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FIA REPLY

Hello Rolando,
We do not sell fuel tanks, but if you want to contact Moeller I'm sure they will get you what you need.
 
 
+2 #7 Peter Eikenberry
I am considered by some to be an "expert" on fuel tanks and your article nails it very well. You presented all the pros and cons. I might note that both plastic and aluminum tanks have to meet USCG requirements for fire resistance and the plastic tanks do it just as well as metal tanks. Also the new plastic tanks that meet US EPA standards do not permeate vapor anywhere as much as ones made before 2012. So smell should no longer be an issue. Baffling is an issue on large tanks and if you are going to much more than 100 gallons you should have baffles to reduce sloshing. That means metal.

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FIA REPLY

Hi Peter...great to see an expert chime in and give the article a thumbs up. Good note on USCG fire rating. Thanks for the comment. Happy boating / fishing.
 
 
+1 #8 ALBERT POPALIS JR.
Thanks for posting this info.I am looking to retank my 96 mako and feel better advised in doing so.Plastic seems to be the best solution for a 55 gallon tank based on your info.As you trust Moeller I will give them a look. Thanks.

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FIA REPLY:

Thanks for dropping by Albert. You won't be disappointed in Moeller tanks. Let me know how it goes. Be sure to follow the install procedures. You can see mine by clicking the link in the article for the 225 Project Aquasport. Best of luck to you.
 
 
0 #9 miguel Valdivia
This was just the type of reading I was looking for. Retanking my 1990 arriva 2450. Had a 60gal aluminum tank that was shot, was able to find a similar shape and just moeller tank but had to drop down to 52gal. I dont think ill miss the 8gals,only doi g lakes and pulled out the 454carb for a 350efi. Found a moeller tank with two vertical round tube shaped cut outs in the middle of the tank to act as baffles.

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FIA REPLY:

Glad the article helped. Thanks for leaving a comment, and happy boating/fishing! FIA
 
 
0 #10 JG
Indeed thank you all for the useful comments. I was confused between plastic and aluminium for my Rybovich rybo runner 30feet 1984, well it is about time it leaks, so I guess for a tank of 180 gal aluminium should be better especially that Moeller does not have the shape I need and customized one will cost a lot. Ps correct me if I am wrong.
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FIA REPLY:

Thanks for the comment JG. You are correct. It will be a lot cheaper to have a fuel tank made from metal in this size. Happy Boating.
 
 
0 #11 zchkhaidze
On my plastic fuel tank manufacturer print
producing year, month and even date. Will it means my plastic tank has a certain shelf live date
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FIA REPLY:

All tanks will eventually wear out, so in a since, yes that would be a shelf life. Old tanks are built like they are today with the new material, so if you are doubting your tank, the wise choice is to get a new one and it'll outlast your boat.
 
 
0 #12 Mohammad ALKhabbaz
Good article I am in the process of changing my 80 gal tank and I am going for the aluminum :D , it's good I didn't go with the fiberglass tanks as I read they react with ethanol.

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FIA REPLY:

Can't go wrong with aluminum tanks as long as you install them correctly and don't foam to the tank. Best of luck and thanks for the comment.
 
 
0 #13 mark tappert
how much air flow do you need under a aluminum tank

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FIA REPLY:

It's doesn't matter how much, just keep a gap so air can flow around the tank, and also for expansion. I would do as much as possible, but no less than 1/2 inch. The other aspect is to ensure the tank is above the bilge water level. I put a bilge blower in my last boat that forced air around the tank. After trips I would run the blower for a few hours on a hot day.