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Author Topic:   Sacrifical Anode on Aluminum Fuel Tank

elvis posted 06-21-2014 12:25 PM ET (US)
Hi all, I'll be ordering my new under deck aluminum 63 gallon tank soon, maybe next week, and one of the options on corrosion protection I read about was a ceramic coating, or paint, versus leaving tank as bare aluminum.
An article I read offered good suggestions on why bare aluminum is good, as it suggested a protective layer of aluminum oxide forms on bare aluminum and gives it a natural protection, so to speak, as some USCG boats are bare.paint and ceramic works fine until a chip or break in the coating occurs, and saltwater gets underneath and speaks, doing its nasty thing.
I'm leaning toward bare aluminum installation, as, for another thing, I believe it came that way originally from Whaler on a 1987 Guardian 18.
With all of this said, I wondered why I couldn't attach one or more sacrificial anodes to the tank, similar to what an outboard uses? Would that be a good idea? Why? Or, why not? It's bound to get wet under the floor with saltwater. I just thought this would be a good idea. Thoughts?
If so, I could have the new tank manufacturer weld a special anode attachment plate to the tank top at the rear.
contender posted 06-21-2014 01:50 PM ET (US)
Elvis I would do the spray lining such as LineX, The only time you would chip the tank is if you move the tank before it dried or you had an accident with it. Try to scrap a pick up bed that has been sprayed with this stuff. Once the tank is in place it does not move anymore therefore there sould be no contact with anything that could chip the LineX, even if it could.
deepwater posted 06-21-2014 05:10 PM ET (US)
I have done all my trucks and rocks just bounce off. I did my deck and all the things the guys dropped like soda cans, beer, 10 oz sinkers, cannon ball down riggers, knives, and the anchor never made to the gel coat again
contender posted 06-22-2014 10:26 AM ET (US)
Deep: What color did you do your decks? Do they make a white or an off-white color of this spray liner?
jimh posted 06-22-2014 05:03 PM ET (US)
Elvis--Concerning your invention of using a sacrificial anode to protect an aluminum fuel tank mounted in a fiberglass boat in a sealed well: I don't think it will provide any protection. Fiberglass boats with aluminum fuel tanks have been around for about 50-years. If a sacrificial anode was the cure, I think someone would have come across this concept before you have in 2014.
Galvanic corrosion occurs when there are dissimilar metals in the same liquid and some electrical current is flowing between those metals. What other metal is in the water in the fuel tank cavity besides aluminum? And what current is flowing between them? The tank is already bonded to the boat battery negative or to its own anode on older Boston Whaler boats (the bronze anode on the transom).
ALAN G posted 06-22-2014 05:15 PM ET (US)
Elvis, a zinc on your tank will accomplish nothing....unless the tank is immersed continuously in salt water. Galvanic corrosion protection (sacrifical anode) needs a complete electrical circuit to function. In the case of underwater metals, the circuit is completed by the electrolyte (sea water). This causes the zinc to be eaten away while protecting the aluminum or bronze or stainless or whatever more noble metal the zinc is protecting. You can read about it by searching the web for galvanic corrosion. Many articles have been written on the subject.
With regard to painting or not painting aluminum there is no clear answer. While corrosion experts agree that covering a surface with a coating to keep water and air away from the surface is the right thing to do, having a small breach in that surface can cause accelerated corrosion starting in the breaches...leading to pits and the corrosion continuing by "burrowing" under the coating. It is somewhat an economic issue too, as the cost of putting a good coating on the aluminum can be significant. People have had success both ways. Again, lots of articles on the web about aluminum boat tanks and to coat or not to coat. I think in general, if the tank will be dry, no coating is best and cheapest. If the tank is wet occasionally with salt water, perhaps the proper coating is worth the cost. Sometimes it is best to specify thicker aluminum if weight or the additional cost is not an issue. Steel ships are built with a "corrosion allowance" added to the thickness needed just for structural strength, recognizing, that in the marine environment, corrosion happens. You can only minimize its bad effects, not prevent it.
Al
elvis posted 06-22-2014 09:17 PM ET (US)
I appreciate all the helpful replies and good information.
deepwater posted 06-23-2014 07:46 PM ET (US)
contender,,I went a shade liter than battleship gray,,The stuff is awesome,,fish stick when thrown

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Author	Topic: Sacrifical Anode on Aluminum Fuel Tank
elvis	posted 06-21-2014 12:25 PM ET (US) Hi all, I'll be ordering my new under deck aluminum 63 gallon tank soon, maybe next week, and one of the options on corrosion protection I read about was a ceramic coating, or paint, versus leaving tank as bare aluminum. An article I read offered good suggestions on why bare aluminum is good, as it suggested a protective layer of aluminum oxide forms on bare aluminum and gives it a natural protection, so to speak, as some USCG boats are bare.paint and ceramic works fine until a chip or break in the coating occurs, and saltwater gets underneath and speaks, doing its nasty thing. I'm leaning toward bare aluminum installation, as, for another thing, I believe it came that way originally from Whaler on a 1987 Guardian 18. With all of this said, I wondered why I couldn't attach one or more sacrificial anodes to the tank, similar to what an outboard uses? Would that be a good idea? Why? Or, why not? It's bound to get wet under the floor with saltwater. I just thought this would be a good idea. Thoughts? If so, I could have the new tank manufacturer weld a special anode attachment plate to the tank top at the rear.
contender	posted 06-21-2014 01:50 PM ET (US) Elvis I would do the spray lining such as LineX, The only time you would chip the tank is if you move the tank before it dried or you had an accident with it. Try to scrap a pick up bed that has been sprayed with this stuff. Once the tank is in place it does not move anymore therefore there sould be no contact with anything that could chip the LineX, even if it could.
deepwater	posted 06-21-2014 05:10 PM ET (US) I have done all my trucks and rocks just bounce off. I did my deck and all the things the guys dropped like soda cans, beer, 10 oz sinkers, cannon ball down riggers, knives, and the anchor never made to the gel coat again
contender	posted 06-22-2014 10:26 AM ET (US) Deep: What color did you do your decks? Do they make a white or an off-white color of this spray liner?
jimh	posted 06-22-2014 05:03 PM ET (US) Elvis--Concerning your invention of using a sacrificial anode to protect an aluminum fuel tank mounted in a fiberglass boat in a sealed well: I don't think it will provide any protection. Fiberglass boats with aluminum fuel tanks have been around for about 50-years. If a sacrificial anode was the cure, I think someone would have come across this concept before you have in 2014. Galvanic corrosion occurs when there are dissimilar metals in the same liquid and some electrical current is flowing between those metals. What other metal is in the water in the fuel tank cavity besides aluminum? And what current is flowing between them? The tank is already bonded to the boat battery negative or to its own anode on older Boston Whaler boats (the bronze anode on the transom).
ALAN G	posted 06-22-2014 05:15 PM ET (US) Elvis, a zinc on your tank will accomplish nothing....unless the tank is immersed continuously in salt water. Galvanic corrosion protection (sacrifical anode) needs a complete electrical circuit to function. In the case of underwater metals, the circuit is completed by the electrolyte (sea water). This causes the zinc to be eaten away while protecting the aluminum or bronze or stainless or whatever more noble metal the zinc is protecting. You can read about it by searching the web for galvanic corrosion. Many articles have been written on the subject. With regard to painting or not painting aluminum there is no clear answer. While corrosion experts agree that covering a surface with a coating to keep water and air away from the surface is the right thing to do, having a small breach in that surface can cause accelerated corrosion starting in the breaches...leading to pits and the corrosion continuing by "burrowing" under the coating. It is somewhat an economic issue too, as the cost of putting a good coating on the aluminum can be significant. People have had success both ways. Again, lots of articles on the web about aluminum boat tanks and to coat or not to coat. I think in general, if the tank will be dry, no coating is best and cheapest. If the tank is wet occasionally with salt water, perhaps the proper coating is worth the cost. Sometimes it is best to specify thicker aluminum if weight or the additional cost is not an issue. Steel ships are built with a "corrosion allowance" added to the thickness needed just for structural strength, recognizing, that in the marine environment, corrosion happens. You can only minimize its bad effects, not prevent it. Al
elvis	posted 06-22-2014 09:17 PM ET (US) I appreciate all the helpful replies and good information.
deepwater	posted 06-23-2014 07:46 PM ET (US) contender,,I went a shade liter than battleship gray,,The stuff is awesome,,fish stick when thrown