One unfortunate side effect of immersing metals in seawater is corrosion. A specific type of decay known as galvanic corrosion can happen when two kinds of metal are connected and then exposed to salt water.  In layman’s terms, this causes the metals to behave in a battery-like fashion; current will begin to flow between them as electrons from the atoms of one of the metals are converted into metal ions and lost into the seawater.  Galvanic corrosion usually proceeds at a rapid pace and destroys the metals involved.

This is obviously a large problem for boaters.  Propellers are frequently mounted on shafts made of stainless steel, but those same propellers are themselves made of other metals such as aluminum or alloys such as bronze.

Avoiding Galvanic Corrosion: The Role of Anodes

In order to avoid forming a battery circuit, designers of boats and motors have long used the technique of the anode.  This involves providing a third type of metal such as zinc, which is placed in electrical contact with the other two metals involved.  Designed to be “sacrificed,” this third metal has inherent qualities that cause it to readily lose electrons.  Since nature takes the path of least resistance, the zinc anodes will decay and eventually be replaced so that shafts and propellers can remain pristine.

Boat zincs can also help to protect other watercraft elements such as rudders and hull plates.  These zincs take a variety of forms including round plates, rectangular plates, and cylinders designed to encircle a propeller shaft.

Tags: boat zincs

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