Corrosion is your boat’s worst enemy. Choosing the right anode for your boat is about as crucial as putting gasoline in the tank. It’s not as easy as it might seem. We’ve put together some basic information on anodes and what factors you need to consider when purchasing one for your boat.
The most common anodes are made of either Zinc, Aluminum or Magnesium. They are measured according to their voltage. The higher the anode’s voltage, the more freely it gives up electrons. This in turn equates to the ability to better feed corrosion.
Magnesium has the highest voltage, followed by Zinc and then Aluminum. Magnesium does offer more protective electrons faster (due to its higher voltage), however it protects for only 1/3 the time of Zinc and 1/5 the time of aluminum. When you take a look at cost, Magnesium is more expensive than Zinc while Zinc is more expensive than Aluminum.
If you compare Zinc and Aluminum, Zinc forms an insulating oxide film over itself, especially in fresh water. This insulating oxide film stops the anode from working. By mixing iridium and other metals with aluminum, alloys are created that don’t form aluminum oxide.
Caution should be taken, though, when using magnesium anodes because they have a higher chance of overprotecting. If used on an aluminum sterndrive or outboard motor it can be incredibly dangerous. For instance, if you take your boat down river to the ocean with magnesium anodes, the overprotection causes hydrogen bubbles to form under the paint on the drive resulting in the paint being blown off. Caution should be taken when putting magnesium anodes on aluminum-hulled boats as well since the same thing can happen.
Aluminum alloy is the only anode material that is safe for use in all types of water. Aluminum is also accepted by the major sterndrive manufactures as the best material to use. It is lighter and protects better than Zinc and it’s not so active that it becomes dangerous like Magnesium. Aluminum alloy is also environmentally friendly, unlike Zinc which is considered a pollutant.
Regardless of the type of anode you choose, it is important to ensure they are made to the appropriate marine specification. Installing cheap or sub-standard anodes will cause increased and potentially very expensive corrosion problems. That’s why you have the satisfaction of knowing when you purchase your anode from Sierra, you are backed by our customer satisfaction warranty!