• MON-FRI: 8am - 6am | SAT: 8am - 2pm
  • 546 Mcmunn St. South Lyon, Michigan 48178
  • 248-486-8300
  • MON-FRI: 8am - 6am | SAT: 8am - 2pm
  • 546 Mcmunn St. South Lyon, Michigan 48178
  • 248-486-8300

Marine Anodes – What Are They?

Marine Anodes – What They Do

When you head out to the boat with your family and friends the goal is to relax and enjoy the time you get to spend out on the water. I bet that most of you had no idea that a battle is under way just below the surface. While you sit back and sip on your favorite adult cocktail, your anodes are hard at work protecting your boat and keeping your gear case and other soft engine parts safe from the devastating effects of galvanic corrosion!

The science behind boat anodes is simple. When you place two different metals together and place them under water they  become a battery. The two metals create a current that will flow from one metal to the other. The chemical reaction causes one of the metals to microscopically dissolve in the form of metal ions. The metal ions in the lake or seawater will try to attach itself to the harder of the two metals in the form of electrolysis. Galvanic corrosion can quickly destroy underwater metals without prevention.

Corroded Gearcase2

In most cases the galvanic corrosion will affect bronze or aluminum propellers which are mounted to a stainless-steel propeller shaft. Don’t think it is limited to attacking propellers! Galvanic corrosion has no problem attacking outboard gear cases, struts, stern drives, rudders, and even trim tabs. It is truly an equal opportunity destroyer.

The good news – Most boats come with sacrificial anodes already in place. Unfortunately, most boaters don’t know that they exist or how important they actually are. The rule of the anode is to change them before they become depleted by 50%. They are called sacrificial anodes because they are supposed to be consumed by the damages of corrosion. Galvanic corrosion and electrolysis cannot be stopped. Your anodes take one for the team and allow themselves to be sacrificed in place of expensive motor parts. Next time you are on your boat, tip up your glass and toast the mighty sacrificial anode!

Corroded Gearcase
On the left we have a gear case that was subject to galvanic corrosion without anodes. In this case, it happened over a long period of time. In extreme cases, this type of damage can be caused in weeks and sometimes even days under the right circumstances.
On the right we have an extremely depleted set of anodes desperate for change and well past expiration. 
Corroded Anode

What Type Of Anode Do I Need?

There are typically 3 different anode options. Magnesium, Zink, and Aluminum. Each anode composition is designed for a different type of water. We will make the decision-making process for anodes very easy. Allow a marine repair professional to assess your anodes and make recommendations. If you are the do-it-yourself kind of boater follow these simple 3 rules.

  1. Fresh Water = Magnesium Anodes
  2. Salt Water = Zink Anodes
  3. Brackish Water = Aluminum Anodes

Make sure you don’t paint your anodes. When you paint an anode you have successfully protected it against the galvanic corrosion. Galvanic corrosion will cause blistering of paint and erosion of your engine parts if the anode cannot be sacrificed. By painting your anodes, you have successfully put your expensive boat parts in more danger of electrolysis.

Anode Kit
Anode Kit 3
Anode Kit4


Anode Installation

Anodes need to be connected to the metal in which it intends to protect. By having a sacrificial anode simply in the water does not do the trick. An anode needs to be attached to the item that we are trying to protect. It can be attached directly or by a metal connection point. The good news is that most boat manufacturers have already designed the boat parts with anodes in mind. Most boats have strategically placed anodes already in place. Some can be hard to find but should be somewhat easy to service.

If you are buying a used boat there is a possibility that your anodes have been removed. Probably because the previous owner didn’t realize the importance of such things. Luckily if you’ve made it this far in the article, you are now smarter than the previous owner and will never… ever… remove your anodes without replacing them with new.

We hope that you’ve found this article on anodes educational and entertaining. From your friends at Mutiny Marine, we wish you a happy and safe boating season.

Author ~ Derrick Watkins - Mutiny Marine Inc.