[Indigo2]

I am onboard a 5 year old MY. I am 3 months on this job. This month the owner has had to go through replacing the 600 gal aluminum 3/8 thick tank due to the bottom of the tank suffering from corrosion. It had been eaten through by the algae!??. So needless to say the boat is tore up and the owner is dissapointed at having to pay for this. He is able to deal with this but had hoped to go to the Chesapeake this summer instead of the yard.

So strangely enough, another boat (smaller) comes in with the same problem. This tank was 8 months old and the previous one had failed after 6 months. This owner had a metalurgist examine the AL and the report discussed sulfer eating bacteria creating sulphuric acid to act on the AL. These bugs will also kill SS. These bugs seem to be new on the scene.

Both his and ours are diesel consumers. Both tanks are flat bottomed with no real way to strip the tank.

So my question is to you all: How many tank failures have you encountered recently? Has anyone else info on these NEW hard shelled bacteria? I am hoping to introduce myself to the metalurgist and ask more questions but I am curious as to the responses from the community.

From reading further on the internet I discovered that AL fuel tanks are supposed to have a life of 7-10 years. Now I was on a big AL boat that was over twenty years old. The tanks were part of the hull. I did have the tanks cleaned and examined after purchase and we found no gross corrosion after all that time. Is 7-10 years accurate?

Not to dismiss the fact that condensation will and does affect fuel tanks and SOP is to keep the tanks full to avoid this. But water does get into tanks either from poorly fitting caps allowing salt and/or fresh water to enter. or the condensate. Which would be worse??? The salt or the fresh? Or would it only be the presence of moisture supporting the alge/bacteria that does all the damage.
BTW we are installing a bladder tank with foam baffels called a fuel cell, NASCAR racers use them

Thanks

[CaptPKilbride]

Is it possible to determine what alloy was used to construct the fuel tanks that you are currently having problems with?

[K1W1]

Hi,

Fuel Fungus isn't new on the scene especially in hot humid climates.

These little fellas get kinda full and take a dump, this is where the acid comes from.

Good Fuel Husbandry will keep them at bay or at least under control.

Dose your bunkers as you load them and run your fuel purifier 24/7.

This type of corrosion is also found in aircraft fuel tanks.

[Loren Schweizer]

I would be willing to bet that these tanks sat on wet plywood tank flats and corroded from the outside in... and maybe a faulty bonding wiring as well for corrosion of this magnitude to occur.

[Indigo2]

The tank on my boat was factory installed and the other was a warranty replacement-from a Florida tank manufact. I think it was called a 55/50 alloy.

Bonding was good on the other boat-Ward's checked it out. No corrosion on the outside. Chemist is going to ID the bacteria.

Doesn't anyone think that 6 months is incredibly fast for these diesel creatures to do their dirty work?

KIWI- I have never used one of these Reverso polishers that we have. It is not the Alfa Laval diesel cleaners. However it is just a single septol filter with the ability to drain any water from the bottom of the bowl. (3 gpm flow) This has been in use for about two years. This filter is clean. The routing plumbing and manifolds are a night mare. We have the ability to have suction from one forward tank (failed)or the STB ER tank for polishing. The only return of polished fuel is STB ER tank and then the overflow takes it to the tank that failed. We will now route the overflow to the next forward tank as the new bladder tank will not be used for routine storage -only as needed.

Yes I agree that good fuel management/cleaning is a must and always practiced as well as possible. Check change the o-rings on the fuel caps regularly and a religious user of biocide. I just wondered if the fuel available is contaminated with more bugs or a new type causing other boats to have more problems.

I did do research on the internet . The double hull tankers promote the growth of these bugs because they are insulated from the cooling waters of the oceans. Hence the product stays warmer and they can grow faster.

Thanks

[Garry Hartshorn]

5055 grade aluminium is primarily used in the aircraft industry for high strength stuctural applications, it is not a marine grade and potentialy suffers from corrosion. Marine grade 5086 is not as strong but is most resistant to corrosion most large aluminum yachts are built of this grade. 5052 is also used in the marine industry and is the grade used for tanker trucks ect.

I have just come out of a yard period and one of the tasks completed was to have our tanks cleaned and inspected, we pased with flying colors. 16 years since the tanks were opened lots of sludge in the bottom of the tanks but no corrosion. This yacht was built of 5086.

I would suggest that you get in contact with a specialist in this field and determine what is the best grade for the application.

[Indigo2]

Thanks Garry, Maybe that is the problem. I will check into it on Monday.

[CaptPKilbride]

Originally Posted by Indigo2

Thanks Garry, Maybe that is the problem. I will check into it on Monday.

Thaw was my first thought as well... tanks made of a poor choice of alloy. I have 17 year old aluminum tanks in my ride, and they are doing fine. They have stripping lines so I can strip them annually, and we open up the tank tops every couple of years to get out any accumulated gunk adhered to surfaces.

[Mov-it!]

Originally Posted by Indigo2

BTW we are installing a bladder tank with foam baffels called a fuel cell, NASCAR racers use them

A fuel cell prevents slushing in fast turns and keeps the car balanced under steering. I'm not sure if this sorts the problem. I also expect that bacteria will set inside the foam.

I rather feel that it has something to do with the tank material or the construction. Without pointing a finger at the manufacturer, It could also be a cause electrolysis. Are there any wiring connections or anything made of ferro metal near the tank?

We use interagted tanks which are a part of the structure and of the double bottom of the yachts. These are made of Alustar AA 5059 which is a high grade marine aluminium. The tanks will hold the entire life-span of the yacht.

The tanks are also subject to classification regulations. I would recommand consulting the manufacturer or the shipyard. There's clearly something not in order here.

[Indigo2]

Thanks for the reply Mov-it

I rather feel that it has something to do with the tank material or the construction. Without pointing a finger at the manufacturer, It could also be a cause electrolysis. Are there any wiring connections or anything made of ferro metal near the tank?

I am leaning more towards the tank material myself. I have to do some more research/contact manufacturer of our yacht for specifics. Electrolysis does not seem to be a factor on our boat or the other one.

We use interagted tanks which are a part of the structure and of the double bottom of the yachts. These are made of Alustar AA 5059 which is a high grade marine aluminium. The tanks will hold the entire life-span of the yacht.

I agree, from experience with good quality AL should last. Something is not right.