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Galvanic Action A battery has the ability to do work by storing an electrical charge and is the reaction of two dissimilar metals in solution. Like the battery under water dissimilar metal parts of your boat can act as a single cell battery producing a small voltage. Onboard most boats the use of a sacrificial anodes will protect your boats valuable underwater metal components. Because zinc or aluminum anodes are more electro active then your boats metal, the zinc anodes are eaten away instead of your shafts propellers or other metal parts.

Galvanic Corrosion analyses and solutions Galvanic corrosion weakens metal components by leeching away alloying elements like zinc. An example of leaching may be found looking at a bronze propeller. Bronze is an alloy of mostly copper some zinc and a few other metals. If the propeller is not protected zinc being the most active metal will be leached away from the propeller that why it begins to look pink its a copper propeller. Once bronze the zinc has been removed because the shaft had insufficient little or no protection from the sacrificial zinc.

Electrolysis AC or DC This type of corrosion can be very dramatic with large volumes of metal removed quickly from shafts propellers or any underwater component made of metal. In only one week the destructive removal of metal can render a component unusable.

shaft stray current corrosion

HYDROLYSIS: Describes Ion movement within aqueous solutions. Meaning in water metal ion particals that are positively charged will move toward a negatively charged Cathode. Further the positively charge Anode i.e. (zinc) will be eating away..as negitive metal ions are made availible.

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The photograph documents damage caused by battery stray current after only 14 days

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