Sacrificial anodes, sometimes referred to as zinc anodes, are essential to boat maintenance.

Since zinc was the first substance utilized for sacrificial anodes, the name "zincs" has come to refer to them. But other metals, including magnesium and aluminum, can also serve as sacrificial anodes.

The relatively cheap metal used to make a sacrificial anode will corrode in place of your boat or yacht's more costly metal elements, such as the sterndrive, propeller, rudders, shaft, and other essentials. Your metal components won't corrode when submerged in water for extended periods of time since the anode's metal is less "noble" and will corrode first.

All three anode types—zinc, aluminum, or magnesium—have a role in corrosion prevention, depending on a number of variables which will be explained here.

The Advantages of Aluminum Anodes

Aluminum anodes are favored over zinc or magnesium anodes by many manufacturers and boaters for a few reasons.

• Aluminum has become more affordable in recent years, which has made it a more appealing option for manufacturers to put sacrificial anodes on their new engines, strainers, heat exchangers, containers, etc.

• A little in fresh water, fair in brackish water, and well in salt, zinc anodes provide protection. Aluminum anodes provide good protection in freshwater, decent protection in saltwater, and good protection in brackish water in the upper levels but poor protection in the lower ones. But aluminum passivates (forms an oxide coating) more quickly than zinc. Aluminum will work if it is cleaned frequently. Otherwise, the aluminum anode may get "passivated," which would make it ineffective.

• According to EPA data, magnesium can be used to create sacrificial anodes. Secondly, aluminum anodes are more environmentally benign than zinc anodes, yet even in the worst-case situation, zinc has very little effect on the environment. [1]

Having said that, an aluminum anode should be your sacrificial anode if you are a boater who frequently shifts between fresh and saltwater or who frequently navigates brackish waters. Compared to the other metals, it is more affordable, has a longer lifespan, and is better able to withstand the change in water kinds.

Think about your location if you plan to keep your boat in saltwater alone. In extremely warm tropical waters, higher water temperatures produce more dissolved oxygen, which speeds up corrosion and puts greater strain on anodes, shortening their service life.

Using Magnesium Sacrificial Anodes: The Freshwater King

Although aluminum and zinc anodes are applicable in freshwater, magnesium (Mg)[2] anodes outperform both aluminum and zinc anodes in this environment.

Freshwaters' high resistance [3] requires MG's large current output. Magnesium anodes are the greatest option for freshwater, particularly if your vessel will be immersed for extended periods of time, even though they are more costly and have shorter lifespans than zinc and aluminum anodes.

The risk of overvoltage (hydrogen release) caused by magnesium's high current output in saltwater can be minimized by using smaller or fewer magnesium anodes; nonetheless, the life of a magnesium anode in saltwater is typically too short to be a good option there.

Where Zinc Anodes Still Reign Supreme

When it is docked or anchored in seawater for extended periods of time, zinc is the best material to use as a sacrificial anode.

Compared to other metals, zinc anodes are superior in "sloughing" off any film accumulation, exposing new zinc alloy to the water, and maintaining the anode's electrochemical activity over time. In aluminum anodes, the consumed metal may film over and create a crust or barrier that will passify the anode if this enhanced sloughing ability is not present.

Anode passivation is more likely the longer the vessel is left in place.

Anodes are reactivated while a vessel is moving because the electrical current produced by the flowing water generates a demand on them. Regardless of the metal type, cutting through the water also removes the oxide deposit from the anode.

Both zinc and aluminum anodes will function if a vessel is regularly used in seawater. Zinc anodes are the best option if you want to sit in saltwater for extended periods of time.

How Do Anodes Work?

In theory, a battery is created whenever two different metals are submerged in water and physically or electrically connected. A certain amount of current will flow between the two metals.

One of the metals contributes electrons to the current by releasing pieces of itself into the seawater as metal ions. Underwater metals on your boat will gradually deteriorate if corrosion is not controlled.

Although struts, rudders, outboards, and stern drives are also susceptible to corrosion, aluminum props on stainless steel shafts are the most common victims.

An electrical current is created towards the less noble metal, which will receive the current, by introducing a second metal (a more noble anode), enabling the anode to sacrifice itself through an ion transfer.

When To Change Your Sacrificial Anode and Other Tips

There are some rules you should adhere to regardless of the material you choose for your sacrificial anode in order to maintain the integrity of your anodes and prevent any kind of corrosion of your boat's essential parts:

• When corrosion has reduced the anode to about half its original size, replace it. You might want to increase the anode's size and weight if this happens within a year.

• A zinc anode needs to make electrical contact with the metal it is intended to protect in order to function. For example, directly in front of the prop on the prop shaft. It can also be connected with a wire if direct contact is not possible.

• Paint or any other coating should never be applied to an anode as this will make it ineffective.

• You can utilize a variety of anode metals, but avoid mixing them together. For instance: Since the protection of the shaft and prop is relatively isolated, a different kind of anode is acceptable.

• Prior to installing the anode, it is crucial to ensure that the surface beneath the zinc is bright and bare in order to guarantee proper electrical contact.

The anode story's lesson? Instead of spending out thousands of dollars for a new propeller shaft or stern drive, it is more cost-effective and time-efficient to change the anodes on a regular basis.

[1] Zinc inputs to coastal waters from sacrificial anodes.

[2] Magnesium, periodic table.

[3] Resistance