Galvanic Corrosion

Technically, corrosion is the attack and progressive destructions of a metal by means of a chemical action. Galvanic corrosion, which is characterized by its destructive power, comes from an electrolysis phenomenon between two metals of different electrical potential that is in contact and in the presence of humidity.

Between the metallic parts of the boat that have contact with water like the propeller, rudder, cooling systems and some connections, can be a current flow, and therefore a corrosion of metallic pieces, even if the metals are physically connected (like the rudder and its ironworks, the propeller, the axis and the motor, etc.), or not.

Certain metals, “Common” called, are corroded faster than the ones known as “Noble” metals. To the right, there is a list of the most used metals in facilities and marine equipment, in an order from minor to greater degree of galvanic corrosion that they can get to suffer, both in marine water and at room temperature.

Since galvanic corrosion occurs on a variety of different metals, to avoid it or to diminish it considerably, it is recommended to use metals of the same type between connections. In case of having different metals in which there is a water flow, it will be necessary to isolate them one from the other. When different metals cannot be isolated, the metals to use on the union must be of a nobler metal than the one of the pieces which they hold to, therefore the corrosion will happen in these ones and not in those of union.

It is necessary to avoid alloys that contain common metals like brass for example, which lasts very little under the water. The most effective method to resist the galvanic corrosion is protecting all the submerged equipment or machinery with pure zinc, joining it to the metal to protect or connecting it with a metallic band.