There are more misunderstandings about anode protection (zincs) for fresh water boats than any other topic around inland marinas.
As a regular boater and fisher, I visit both fresh and salt-water marine locales. I often hear that fresh water boats don’t even need anodes, or that zinc anodes are fine because they last forever, or that boaters shouldn’t mix anode metals with different metals underwater. Wrong, wrong and wrong.
Any boat that stays in the water needs anode protection, whether in salt or fresh water. Almost any boat today has a mix of metals, steel fasteners, bronze props, aluminum outboard housings, etc. Any two different metals under water will cause a small electrical current that will steadily corrode one metal. Sacrificial anodes are the solution and we’ve been using them for decades, no, make that centuries now.
It’s true that salt water is a better conductor than fresh water but both environments need anode protection for boats that have any metal parts under water. Fresh water has sufficient impurities that it too conducts electricity, and therefore causes corrosion. Boats kept in fresh water do need anode protection.
It’s also true that zinc anodes will last forever in fresh water. That’s because zinc anodes don’t work at all in fresh water. Their chemistry is all wrong! In pure fresh waters such as inland lakes and rivers only magnesium alloy anodes will provide corrosion protection. In brackish waters such as tidal estuaries or rivers (such as the Fraser River where I keep my boat) boaters can use aluminum anodes, but never zinc.
Recent research has also shown aluminum to be a better choice even for salt water, as zinc anodes all contain amounts of cadmium, a known heavy metal that is toxic even in small concentrations. Remembering that anodes are sacrificial, that is they are slowly “eaten away”. the metal bits are slowly released and they fall to the bottom. Zinc plus cadmium just adds to the toxic build-up in harbors and marinas.
Let’s not do that. Let’s make sure our anode protection is at work for our boats. Use aluminum in salt or brackish waters and use magnesium in all fresh water applications.
NOTE: Possible reference to manufacturers recommendation about anode protection and replacement parts for outboards and stern-drives.
Canada Metals (Pacific) Limited, Delta, BC, Canada (Martyr Brand), www.canmet.com