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What Causes Boat Anodes to Become Ineffective?

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Many boat owners know that they need to replace the anodes on their boats regularly in order to prevent the corrosion of important parts, such as the propellers. However, boat anodes can still fail to do their work even if they are changed regularly. This article discusses some of the factors that can make boat anodes ineffective.

Wrong Choice of Anode

Boat anodes are made from different metals, such as zinc, magnesium and aluminium. Each of those types of anodes is best suited for a different type of water. For instance, magnesium anodes are best suited for freshwater. This is because they are very conductive and can protect the boat's parts in such water whose conductivity is low.

An anode will become ineffective if it is used in a type of water for which it is not suited. For instance, zinc anodes will become ineffective if they are used in freshwater. This is because the anodes will form a hard coating (hydroxide) on their surface. That coating will prevent the anode from performing its role of sacrificing itself so that sections of your boat don't corrode.

Stray Currents

Stray currents refer to electrical energy that finds its way into the galvanic cell (the electrical circuit formed when a cathode, such as a boat propeller, and an anode are immersed in water). That stray current may flow from damaged insulation in your boat. A wet wall on the boat can act as the transmission channel to direct the stray current into the water on which your boat is floating. Such a stray current can increase the conductivity of the water.

That increased conductivity may accelerate the rate at which the anode is consumed by corrosion.  For instance, a magnesium anode will corrode rapidly in the presence of a stray current. You may be comfortable in the knowledge that your boat has new anodes, but you can be shocked to discover that boat parts failed due to corrosion that was accelerated by a stray current that you were unaware of.

Cathode Shielding

Cathode shielding refers to the use of a protective coating, such as polyethylene tape, on the surface of a metal, such as a propeller, that should be protected from corrosion by an anode. That coating prevents ions from the anode from crossing to the metal being protected. When that happens, the cathode (metallic part of a boat) starts corroding because the anode isn't corroding in its place.

As you can see, caution must be exercised when maintaining a boat. Any changes in the rate at which an anode is consumed should be investigated immediately so that the anomaly is fixed before the anode becomes ineffective. Contact a company like Carman Heating for more information about working with anodes.