Aluminum versus stainless steel fuel tanks

[kmacdonald]

Originally Posted by Cheechako

ABYC is voluntary. It's not a gov't agency.

And it's members and contributors have products they want to sell and a desire for the ABYC to require them. They also want to use the ABYC as a standard that if they meet it they won't be liable for damages. Of course the ABYC "suggestions" don't carry a lot of weight in a courtroom. Manufacturers who are members (pay dues) and claim compliance are often times not in compliance. I've never heard of the ABYC taking any action if their dues are current. Just a WAG.

[Taipe]

Speaking from the experience of others, it seems that most pinholes in stainless steel tanks are occurring at the weld joints due to inadequate inert gas at the weld when the seams are being welded, allowing oxygen to contaminate the weld. Apparently this occurs most often when the tank is welded in windy outside conditions. But, even when a ss tank is being fabricated inside a shop, wind gets inside if the bay doors are open.

[Cheechako]

Originally Posted by hpeer

Muntil the insurance company adopts those standards. Then it’s mandatory, at least for that insurance company.

So YOU must use tinned Wife, but Yanmar is not required to do so. FBS.

So if the Ins Company mentions ABYC, and ABYC is voluntary... are you in compliance if you do nothing?

[Taipe]

Unless the tank can first be removed, it might need to be painted on, to reach vertical seams and side walls. Baffles sometimes create an obstacle to direct vision/application. Not infrequently, a diesel tank is installed during construction, making it impossible to remove in one piece.

It seems like the ideal application would be to treat a tank that can be removed for adequate steam/detergent cleaning and thorough drying.Also, do you know if this product might trap fuel filters if not thoroughly adhered to the tank surface?

Originally Posted by hpeer

In my wanderings I have come across a 2 part epoxy that is used to seal tanks in aircraft wings. It is marketed in the marine world by the Boat Life caulk folks, but can be had cheaper and in more formats from the aviation industry.

I’ve no idea WHY you are replacing your tanks, or how far along, but this stuff is a honest to goodness repair product. So maybe don’t replace, but use this on the inside as a repair of your leaks. The tanks must be clean obviously.

There are 2 types, pourable and heavy. The heavy will seal up to. 1/4” vertical crack. And they do have a shelf life, don’t keep forever.

This is the heavy

Life-Calk Two-Part Sealant Type H (Heavy) 750ml - BoatLIFE

[hpeer]

It’s used on passenger airplanes, I suspect it’s been pretty well vetted.

[hpeer]

Originally Posted by Cheechako

So if the Ins Company mentions ABYC, and ABYC is voluntary... are you in compliance if you do nothing?

I don’t even know what that means.

My personal experience is some idiot surveyor comes by and writes me up for something he claims is in the ABYC. For instance that the stove “must” be gimballed. So because he has written it up the insurance company requires me to address it. The underwriter is in no position to mediate an argument, he will just go with the surveyors recommendation, period.

Same surveyor who told me he wasn’t going to write me up for having Two 6 volt GC2 batteries in a steel boat, because ABYC allows it, but it’s a really, really bad idea. And other jems.

[a64pilot]

Originally Posted by hpeer

In my wanderings I have come across a 2 part epoxy that is used to seal tanks in aircraft wings. It is marketed in the marine world by the Boat Life caulk folks, but can be had cheaper and in more formats from the aviation industry.

I’ve no idea WHY you are replacing your tanks, or how far along, but this stuff is a honest to goodness repair product. So maybe don’t replace, but use this on the inside as a repair of your leaks. The tanks must be clean obviously.

There are 2 types, pourable and heavy. The heavy will seal up to. 1/4” vertical crack. And they do have a shelf life, don’t keep forever.

This is the heavy

Life-Calk Two-Part Sealant Type H (Heavy) 750ml - BoatLIFE

It’s not an epoxy, it’s a polysulphide.
Don’t ask me the difference though, I have no idea.
In aircraft it’s usually available as either A or B. The A is thin and runny like 5200. The B is ticker like silicone caulk is.
Then there is a number, usually from 1/2 to 2. That is the “pot life” from a half hour to 2 hours.

95% of what is usually used is B2, so much so that it’s often just called that in an aircraft factory, you ask for some B2 when you need fuel tank sealer.

It has been around for longer than I have, many, many aircraft fuel tanks are the actual wing itself, which is slap full of hundreds of holes of course cause it’s riveted together, added to that is that it is constantly flexing and operates between likely 150F on a sunny day in Kuwait and -100 for a jet in cruise flight.
It seems to last about 30 years before a wing has to be resealed, which is a job you don’t want, all of the old has to be removed and the wing has to have all traces of fuel residue removed, or the reseal will fail.

But it’s about as durable of any kind of “liquid rubber” as anything I have ever seen, has a bond at least as strong as 5200, I think stronger, and almost nothing will remove it except physical force, it seems pretty much impervious to almost anything.

[catman]

I removed the aluminum tank from my F/P cataman, mounted fore of the steering station.
Had to cur galley out to remove the tank.
The bottom was pitted from errant coins that had made their way underneath the tank.
The tank was replaced with two bladder tanks, one in each hull.

[Coltrek]

I have a shop, I have made SS fuel tanks even tho I suggested they buy plastic. I have repaired Aluminum tanks complaining the whole time he should scrap it and buy plastic, (He is my buddy, and he did replace with plastic a couple weeks later after a new leak appeared).
I replaced the Steel tank on my C&C with a Poly Tank.
You can probably guess, I lean more towards Poly tanks.

[Ken Pole]

Completely agree that Moeller is the best option, be it water or fuel. They have a broad range of prefabricated tanks and, I believe, will custom fabricate. Can't recommend them highly enough.

[David M]

High density polyethylene will never corrode and you can get it in many different volumes and shapes.

[Farlander]

I have read all the blah blah blahs but it seems nobody is mentioning the critical detail of permeability.

My understanding is that a polyethylene fuel tank will begin to permeate the odors of the fuel within weeks / months if not sooner.

However a stainless or aluminum tank may take years or never leech odor.

If you had to choose between stainless and aluminum, which would you pick and why?

I have a PE tank already and it is bulgy, dodgy, and vulnerable to puncture or melting. What's so great about PE?

[Manateeman]

When TIG welding stainless, the gas coverage is critical. You need it on BOTH sides of the weld. We see a lot of welders try to ignore this usually because nobody looks at the interior. Lots of other reasons for bad welds, but this is a classic.
Aluminum fuel tanks. The key is to prevent the aluminum from sitting in water.
That’s pretty easy. OR...water sitting in the aluminum. Bit more difficult.
We have two tank pickups. One about a diameter or two above the lowest point in the tank. This is for a water stripper system. Pump, filter and return. Completely seperate from the fuel delivery from the higher pickup to the engines.
No water sitting in the corner of the tank to begin eating it’s way out.
Happy trails.
The manatee crew

[wingssail]

Our boat came with an aluminum fuel tank which is now 40 years old. No problems. We added a second tank, out of stainless steel, 20 years ago and it too has been problem free. Both tanks sit above the bilge in dry areas.

But with water tanks our experience has been just the opposite.

30 years ago we had custom water tanks made in aluminum. Where they sat on the hull there was often a small amount of trapped water, often salty. Both tanks developed leaks where they contacted the water. We replaced them with custom built stainless tanks after 10 years when we were unable to stop the tank leaks. We also worked to keep that portion of the bilge dry but that was difficult due to the inaccessible location and the shallow shape of our hull. Consequently the within the next 12 years the new stainless tanks developed pitting and corrosion and eventually leaks in the same places. (dang!)

In between we had to remove and repair the tanks more than once due to flexing of the thin stainless material which was used. The previous aluminum, even while thicker, was much lighter but did not flex, and the welds stayed solid. It is important to make sure your tanks have baffles which are strongly welded to prevent flexing, and recognize that the stainless tanks will be significantly heavier.

Now we are on our third set of tanks, also stainless, and we have again tried to address the wet bilge issue to prevent corrosion (in addition to heavy coating of epoxy on the outside of the tanks in the affected area).

So in conclusion, whether you use aluminum or stainless, keep them away from contact with salt water. Maybe plastic is better.

[rslifkin]

Originally Posted by wingssail

Our boat came with an aluminum fuel tank which is now 40 years old. No problems. We added a second tank, out of stainless steel, 20 years ago and it too has been problem free. Both tanks sit above the bilge in dry areas.

But with water tanks our experience has been just the opposite.

30 years ago we had custom water tanks made in aluminum. Where they sat on the hull there was often a small amount of trapped water, often salty. Both tanks developed leaks where they contacted the water. We replaced them with custom built stainless tanks after 10 years when we were unable to stop the tank leaks. We also worked to keep that portion of the bilge dry but that was difficult due to the inaccessible location and the shallow shape of our hull. Consequently the within the next 12 years the new stainless tanks developed pitting and corrosion and eventually leaks in the same places. (dang!)

In between we had to remove and repair the tanks more than once due to flexing of the thin stainless material which was used. The previous aluminum, even while thicker, was much lighter but did not flex, and the welds stayed solid. It is important to make sure your tanks have baffles which are strongly welded to prevent flexing, and recognize that the stainless tanks will be significantly heavier.

Now we are on our third set of tanks, also stainless, and we have again tried to address the wet bilge issue to prevent corrosion (in addition to heavy coating of epoxy on the outside of the tanks in the affected area).

So in conclusion, whether you use aluminum or stainless, keep them away from contact with salt water. Maybe plastic is better.

Yes, aluminum and stainless tanks both must be kept dry, inside and out. Personally, I like aluminum for fuel tanks. Mine still look good after 36 years.



For fresh water, aluminum is a mediocre choice. Stainless is a bit better. Plastic or fiberglass is best from a lifespan and corrosion perspective. And plastic or fiberglass only for holding tanks.