First, what do sacrificial anodes do?
Sacrificial anodes “sacrifice” themselves by wasting away instead of the propeller, the propeller shaft, rudder, engine or other metal parts in or connected to the water being” eaten” away or wasting away due to the electrochemical process of corrosion.
Sacrificial anodes are relatively cheap pieces of metal. They are designed specifically to corrode instead of the more expensive metal parts of your boat corroding. Sacrificial Anodes, which are known as “active” metals, are chosen for this task.
Traditionally sacrificial anodes were usually made of Zinc, hence the name “zincs” but they can also be made from magnesium or a special alloy of aluminum. Anodes are very important, indeed essential, even when you trailer your boat, and will help to prevent very expensive damage to the metal parts of your boat that are underwater.
Sacrificial anodes come in all shapes and sizes but they all perform the same task. They have to be connected “electrically” - usually metal to metal - to the valuable metal parts on your boat that need protecting. Thus you will see these gray pieces of metal attached to rudders, outboard motors, propeller shafts etc.
What metals are used in sacrificial anodes?
The three most active materials used in sacrificial anodes are zinc, aluminum and magnesium. They have different properties and uses.
Although Zinc and Aluminum have been used for fresh water for years, they are not the most effective as compared to Magnesium in that environment.
To maximize effectiveness, choose Zinc for salt water, aluminum for salt & brackish water and magnesium for fresh water(only).