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Zinc boat anodes not doing their job!
Q. Is there any other way to prevent Boat Electrolysis besides zinc? And Zinc will only slow down the process -- is there any way to stop it all together?
Bill Jackson- Fort Myers, Florida, United States
2002
A. I believe Magnesium is even more susceptible to galvanic corrosion than Zinc, so that might slow the process more (or the Magnesium bars might just get eaten up faster).
Jim GorsichCompton, California, USA
2002
A. I can't speak for the efficacy of any particular "impressed current system", and presumably it's possible to install them wrong. But the theory is sound--I believe they can stop electrolysis completely.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2002
Q. I am the Boating Officer for a Research Station. We have a fleet of 8 boats, four of which are 5 meter aluminium RIB type dinghies. We have had the same anodes on their sterns for 2 years now and apart from some fouling from sea growth (which we grind off) they don't appear to be degrading. Two of the vessels have quite severe corrosion on the deck to hull weld joints, with the standard white powder and parts of the floor delaminating and lifting. The boats are powered by 30 HP outboards and have no batteries or wiring so we have eliminated stray current corrosion. The boats are connected to a mooring line via aluminium hooks at the stern and a stainless steel clip at the bow. Could this be causing some sort of galvanic corrosion? Any thoughts?!
Cheers
Skipper - Orpheus Island, Queensland, Australia
February 16, 2009
A. It is not really a wonder that your zinc anodes are not degrading as they are the more noble metal than the aluminium your boat is made from. This means your aluminium will corrode to protect your zinc . You should use magnesium anodes for aluminium, Zinc can used to protect steel.
Marcus Hahn- Lucerne, Switzerland
February 23, 2009
A. Must disagree with you, Marcus.
Contrary to your statement, zinc is in fact anodic to aluminium and provides protection in salt water.
In fresh water, the surface of the zinc doesn't remain clean enough and magnesium is needed to protect aluminium. But in salt water, zinc is the standard protection for aluminium.
Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.
February 24, 2009
A. Hi. Bill is right; aluminum vs. zinc is one of those funny galvanic relationships ...
Although the first step in electroplating onto aluminum is almost always an immersion into "zincate", wherein the aluminum dissolves and the zinc plates out onto it, i.e., the aluminum is sacrificial to the zinc ... in more dilute solutions, i.e., the "sea water series", zinc is sacrificial to aluminum.
I always had zinc anodes on my aluminum engines (salt water boats) and they worked fine. Maybe you are expecting anodes on the outside of the boat to protect the inside of the boat when there is no continuous fluid path between the two. Or maybe proper electrical contact is not being maintained between the aluminum and the zinc for some reason. For sacrificial anodes to protect a given area of metal, you must have both a conductive fluid path and a conductive metal path between the two.
Good luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
August 25, 2012
Q. I have a 48' steel boat and was wondering if it is possible to overcompensate with the number of zinc anodes. Can it do any harm, apart from slow me down with all the bumps along the hull?
Paul FieldBoating Enthusiast - Sydney, Australia
2005
A. Hi Paul. I don't think it can possibly have any adverse galvanic effect.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2005
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