Sacrificial Zinc Anodes

Sacrificial anodes can be made of different materials for different uses. The three general metals used are magnesium, aluminum, and zinc. These metals all have different levels of reactivity, and therefore, work better for certain environments.

Traditionally zinc has been the most popular metal to use as an anode. It is great for saltwater use but is ineffective at reducing corrosion in freshwater. When used in freshwater, zincs build up a coating that stops them from working. In high concentrations, zinc can be toxic to aquatic invertebrates, fish, and plants. Read More

As a result, aluminum is becoming more popular for use as an anode. Aluminum alloy anodes are a great option, having grown in popularity for boats that are used in both fresh and saltwater, and lasts significantly longer than zinc. In addition to its effectiveness at reducing corrosion, it is not toxic to marine life.

Magnesium is the most active metal used as an anode. Due to this, it is best suited for freshwater use. It is best to avoid using magnesium anodes in salt water as they will not last long at all, and can even damage some paints due to their reactivity.

Anodes come in different shapes and sizes for different purposes: Read More

Motor Anodes

The smallest anodes, and arguably the most important, are in your motor. On inboard motors, they’re small cylinders placed in the heat exchanger. These small cylinders are referred to as pencil anodes. On outboard motors, they’re small cylinders that bolt into the cooling jacket of your outboard.

Propellers

Propeller anodes can be protected in multiple ways. On large vessels, this is with a propeller nut anode. On outboards, an anode washer can be used, or the anode on the lower unit can be sufficient. Anode specifications for outboards may vary by manufacturer.

Rudders

The rudder or rudders of large inboard boats or sailboats typically have small anodes that do not cause much drag or turbulence.

Propeller Shafts

Propeller shaft anodes go around the stainless steel shaft and bolt together on either side of the shaft. This design is intended to minimize drag and keep the shaft perfectly balanced. Selecting the perfect size is important as poorly sized anodes can cause balance issues and can result in poor corrosion protection.

Clip-on Anodes

Clip-on anodes can supplement a boat's existing anode system to counteract stray currents. They are not intended to replace any permanent anodes. They can be clipped to outdrives or other metal fixtures that need protection. Clip-on anodes can only be used while moored.

Hull Anodes

Hull anodes can be used to protect any electrically bonded accessories or to protect metal-hulled boats. These are typically much larger than other anodes.

Miscellaneous Anodes

Remember, anything below the waterline needs an anode or to be grounded to an anode! This includes trim tabs and through-hulls. Trim tabs have specifically designed anodes. Through-hulls can be electrically connected by wire to an anode.

Zinc anodes are sacrificial anodes, meaning they will corrode and deteriorate to keep the rest of your boat from corroding. Anodes can help to protect your boat from multiple types of corrosion.

Zinc anodes should be changed at least once a year. If you keep your boat in a saltwater wet slip, they may need to be changed more often than if you keep your boat on a trailer. It is best to check on the levels of deterioration on your anodes regularly. Once your anode has corroded to 50 percent of its original size, it needs to be replaced. If your zincs are deteriorating in less than a year, your boat may require additional zincs.

Zinc anodes work well to protect aluminum hulls in saltwater. In freshwater, magnesium anodes work better than zinc for aluminum boats. But never use magnesium anodes on an aluminum hull in saltwater. Magnesium is so active that it can damage the hulls of ships. Aluminum anodes are preferred in brackish water. Always consult your boat manufacturer for the best results.

Yes! Although freshwater is not as corrosive as saltwater it can cause corrosion over time. The type of anode required is different as well. For freshwater use, magnesium anodes or aluminum anodes are recommended, as zinc is not as effective in freshwater.