Anodes & Zincs

Anodes and Zincs Resources and Information

Also known as zincs, trim tab anodes are essential for steering your boat safely and accurately. Periodically replacing your trim tab helps prevent corrosion and ensure your outboard operates at peak performance. PartsVu is proud to stock a wide selection of anodes from leading boating supply manufacturers. Browse our complete selection to find the anode to match your engine's exact specifications. 

Looking for more marine products? Browse the full selection of PartsVu’s aftermarket parts and products and accessories. 

Anodes and Zincs FAQs

What do trim tab anodes do? 

Trim tabs are essential for steering your boat safely and accurately. When properly aligned, trim tab anodes counteract torque pressure generated by the propeller for steering and helps even out “prop-walk,” a propeller’s tendency to rotate about a vertical axis. That’s why it’s called a “trim” tab, enabling a more stable ride that offsets unwanted torque. Trim tabs are often set at an offset angle for this purpose – aligned right for right-turning outboard motors and left for left-turning outboard engines. Most Yamaha outboards have a series of hash marks by the trim tab that indicate the offset needed for accurate steering.

There are three types of corrosion boaters typically experience:

• Simple electrochemical corrosion
• Galvanic corrosion
• Electrolytic/stray current corrosion

Trim tab anodes absorb these types of corrosion more readily than other engine components, so they serve as a protective barrier to save more expensive and harder-to-repair parts. 

Over time, these anodes—typically made of cheap zinc materials—will degrade and need to be replaced. As the material degrades, it begins to lose some of its steering abilities and its ability to attract corrosion. While simply cleaning it with a wire brush will restore it for minor damage, replacement is necessary when corroded to approximately half of its original size. This is why they are referred to as sacrificial anodes—the anode sacrifices itself to protect your engine and its components. 

Checking your trim tab anode(s) (and other anodes, for that matter) should be done minimally as part of your annual or 100-hour service.

What are the other types of trim tab anodes?

Bear in mind that there are several other types of anodes also located in your Yamaha outboard motor. Depending on your model, your Yamaha outboard may have:

• Lower plate/bracket anodes 
• Button anodes
• Internal anodes

While these anodes serve the same anti-corrosion function of the trim tab anode, their function does not affect steering. Replacement is a bit different than trim tab anodes – for example, internal anodes require taking off the engine cover to access them and may only need a light brushing if minor corrosion has occurred.

How do I install an anode?

Now that you understand why trim tab anodes are important for your boat and outboard motor, let’s learn how to install trim tab anode on Yamaha outboards:

• First, identify where the trim tab anode on your Yamaha outboard is. It is typically located above the propeller on the anti-cavitation plate.
• Next, locate and remove the trim tab plug located directly above the trim tab. 
• In the cavity, you will insert a socket wrench with an extension to access the bolt securing the trim tab. Most Yamaha trim tabs use a ½” socket wrench.
• Make a note of the hash marks by the trim tab, which indicates how many degrees they will be offset. Use a piece of masking tape if you have to remember the location so you won’t have to adjust it after installation.
• Slowly turn the bolt counterclockwise to loosen the trim tab until it loosens.
• Insert the new trim tab anode. Replacement is the opposite of installation.

That’s the entire process for replacing a trim tab on a Yamaha outboard motor. Simple!

Now that you know how to install trim tab anode on Yamaha outboards, an outboard trim tab anode adjustment only requires a loosening of the retaining bolt and adjusting according to the hash marks.

Simply adjust the trim tab in the direction it is misaligned – if your boat steers too much to the starboard side, adjust the trim tab right; vice versa for port-side steering. As a word of caution, only make adjustments in one-click increments. Also, make sure the trim tab anode is secure, as a loose trim tab can stray from its original position.

What is the best anode for freshwater?

The best anode for freshwater is made from magnesium. While aluminum and zinc are cheaper alternatives, serving as “catch-all” materials, magnesium helps prevent “potential reversal” at elevated temperatures commonly found in freshwaters. This means that materials besides magnesium may actually draw in unwanted corrosion and electrolysis, especially in marinas where boaters use land power.

Therefore, if you are looking to take your boat out from saltwater to freshwater, it may be wise to perform a Yamaha outboard anode replacement with magnesium anodes.

What are marine rust and corrosion?

Before we get into boat rust prevention, it’s important to understand what the terms “rust” and “corrosion” actually are:

Rust is the name given to iron oxide (Fe²O³), a typically reddish-brown oxide formed by the reaction of oxygen and iron in the catalytic presence of air moisture, or water. Rust occurs in ferrous metals, with iron as part of its composition.

For most boats, iron-containing (ferrous) metals are used for their strength and relative lightweight. However, the proximity to water and humidity eventually corrodes these materials for boats and trailers over time, requiring preventative measures and replacement to keep them seaworthy.

Corrosion, on the other hand, refers to the process of metals being chemically destroyed or worn down by chemical reactions. Rust is a type of corrosion, but it is not the only type of corrosion that affects boats and boat trailers.

Several types of corrosion commonly occur in boats and trailers. As you examine your boat for signs of corrosion, try to identify which kind of corrosion is happening to help you troubleshoot where it’s coming from and how to prevent it.

Atmospheric Corrosion

When metal is exposed to the air that contains moisture and salt

Immersion Corrosion

Metal in water accelerates the corrosion process – especially in warm saltwater.

Galvanic Corrosion

This type of corrosion occurs when dissimilar metals are immersed in a conductive solution (water, saltwater) and are electrically connected. The metal that is more resistant to corrosion (the noble metal) “steals” mass from the other metals (less noble). Mass transfer occurs in the electrolyte (water) – which explains the purpose of sacrificial anodes in outboard and sterndrive motors.

Pitting Corrosion

Pitting corrosion is a localized form where tiny holes and cavities are produced in metals. Because these holes start small when they first occur, this corrosion can be difficult to detect on boats and trailers.

Poultice Corrosion

Poultice corrosion occurs when a metal is covered by absorbent materials, dirt, and debris, trapping moisture against the unprotected metal surface. This is most commonly seen with painted aluminum with water trapped under the paint or butted up against plywood, such as an aluminum fuel tank.

Erosion Corrosion

The constant velocity of moving water gradually wears away the metal. A boat’s trim tab is most likely to experience erosion corrosion.

Stress Corrosion

Hairline cracks can form for metal fittings that have been formed through bending or metal working, eventually branching out from the main crack. As the material weakens through corrosion, these branches – resembling a tree without leaves – spread further and further until eventually breaking under load or pressure.

How do I prevent rust and corrosion on my anode?

Rust and corrosion are progressive, often starting with small signs that are visible with a brief inspection. It’s important to inspect your boat when it is out of storage on a biweekly or monthly basis so that you can spot corrosion and address it before it spreads and eventually leads to mechanical failure.

It’s extremely important to hose down your boat and boat trailer with fresh water after every use. Hosing with fresh water helps remove salt deposits, dirt, and debris that contribute to further corrosion. Be sure to aim for hard-to-reach places and adequately dry any areas where moisture can accumulate.