OEM Yamaha Bracket Anodes

Anodes are typically made of zinc, which is an extremely effective base metal far less resistant to galvanic and electrolytic corrosion than most other metals.

The anodes act as sacrificial metal because they give off their electrons and corrode before the other metals in the motor can be affected. Because corrosion attacks the least resistant metal on a boat’s motor, the anodes or zincs are the first line of defense.

Anodes are consumed first to prevent other parts of the outboard from getting eaten up by corrosion — hence why they’re often referred to as “sacrificial anodes”— giving off their electrons to be depleted before any other metals are targeted. Eventually there will be so little left of an anode that it ceases to be effective, which is why they need to be replaced periodically.

Outboard anodes are typically found mounted low on the transom bracket or under the motor’s ventilation plate, where they also act as trim tabs that compensate for prop-walk and keep the boat pointing straight.

Any time you have two different metals that are physically or electrically connected and immersed in seawater, they become a battery. Some amount of current flows between the two metals. The electrons that make up that current are supplied by one of the metals giving up bits of itself — in the form of metal ions — to the seawater. This is called galvanic corrosion and, left unchecked, it quickly destroys underwater metals.

The most common casualty of galvanic corrosion is a bronze or aluminum propeller on a stainless steel shaft, but metal struts, rudders, rudder fittings, outboards, and stern drives are also at risk. The way we counteract galvanic corrosion is to add a third metal into the circuit, one that is quicker than the other two to give up its electrons. This piece of metal is called a sacrificial anode, and most often it is zinc. In fact, most boaters refer to sacrificial anodes simply as zincs.

It would be hard to overstate the importance of maintaining the anodes on your boat. When an anode is missing or largely wasted away, the metal component it was installed to protect begins to dissolve.