Owning a boat means constantly battling the elements, but one of the most insidious threats isn’t always obvious. Let’s talk about galvanic corrosion.

This silent destroyer can weaken metal components, leading to expensive damage and even catastrophic failure. Understanding how it works and, more importantly, how to prevent it, can help save you time, money, and a whole lot of stress.

The science behind galvanic corrosion

Galvanic corrosion happens when two dissimilar metals, like aluminum and stainless steel, come into contact in the presence of an electrolyte, like saltwater. When this occurs, one metal becomes the “sacrificial lamb,” corroding at an accelerated rate while the other remains largely intact.

Knowing how metals interact is one of the keys to avoiding galvanic corrosion, which is where the Galvanic Series chart (also known as a Electo-potential Series chart) comes in handy. This chart ranks metals from most noble, i.e. the least likely to corrode, to the least noble, which are highly prone to corrosion. The greater the difference between the two metals in this series, the faster corrosion will occur. In the case of stainless steel and aluminum, it’s the aluminum that’ll corrode first.

Getting more technical, in marine environments where the salt air and humidity can accelerate corrosion, it’s best to pair metals that have no more than a 0.15-0.2V difference on the anodic index. In less harsh settings, like a home or freshwater environment, a slightly higher threshold of 0.25V is generally okay.

Galvanic corrosion versus electrolytic corrosion

Sometimes the effects of galvanic and electrolytic corrosion can cause the two to be mixed up, but they do have different mechanisms and causes.

While galvanic corrosion is caused by dissimilar metals contacting in the presence of an electrode, electrolytic correction takes place when stray current leaks into metal components from something like faulty wiring or poor grounding. That stray electrical current forces the metal ions to dissolve into the water, leading to rapid corrosion that typically damages components much faster than galvanic corrosion does.

This damage was done to a stainless steel anchor chain in the period of about a week by stray current corrosion

Real-life consequences of galvanic corrosion

The effects of galvanic corrosion can range from minor surface damage to complete structural failure, so it’s not something to take lightly. Around a sailboat you might find it anywhere that dissimilar metals are touching without protection.

• Aluminum solar panel frames attached to a stainless steel solar arch
• Stainless steel fittings on an aluminum yacht or dinghy
• Catamaran trampoline buttons made of aluminum but held down with stainless steel bolts
• Stainless steel bolts clamping on an aluminum fishing rod holder
• Stainless steel brackets and fixings on an aluminum mast

Galvanic corrosion resulting in dismasting

One notable case of the devastating impact of galvanic corrosion involved a Pantaenius client who experienced a dismasting during a regatta. The boat had suffered no impact or collision during the event. The conditions on the water were fine. There was nothing obvious that had happened that day that may have caused such a huge failure.

Given the circumstances further investigation was warranted, and after the mast was salvaged from the seafloor, it and the mast base were sent off for metallurgy testing. The outcome; galvanic corrosion was found.

It was later discovered that a contractor involved in installing the mast had used stainless steel screws on the aluminum mast. As per the galvanic series, these metals are dissimilar and shouldn’t be used together to avoid galvanic corrosion. The areas where the tradesman put the screws into the mast became weaker over time as the ‘sacrificial’ aluminum corroded away, turning a strong mast into a ticking time bomb.

Preventing galvanic corrosion on your boat

The good news is that galvanic corrosion is avoidable with proper precautions, so to that end here’s some practical actions you can take to manage the risk of it happening aboard your boat.

1. Choose compatible metals

Before installing or replacing any hardware on your boat, check the Galvanic Series chart. If two metals have a voltage difference greater than 0.15-0.2V in marine environments, they shouldn’t be in direct contact. This is especially true for stainless steel and aluminum, two favorites in the marine industry that don’t do well together.

This aluminum vang was constructed using aluminum rivets, with the like metals removing the potential for galvanic corrosion.

2. Use protective barriers

If dissimilar metals must be used together, take steps to electrically insulate them. There are a few ways you can do this.

• Use plastic or rubber washers to separate the metals
• Apply marine-grade sealants to adjoining surfaces, almost like a gasket
• Investigate using corrosion inhibiting products like Tef-Gel, Duralac or CRC Zinc It

Looking at this mast base, can you spot the plastic washer under the block, separating the two metals? This mast was also put together with sealant, Tef-Gel and Duralac to help prevent galvanic corrosion.

3. Invest in sacrificial anodes

Sacrificial anodes, often made of zinc, magnesium, or aluminum, are designed to corrode before your more valuable metal parts do. Regularly inspecting and replacing these anodes is crucial to keeping galvanic corrosion at bay, especially on critical components like sail drives and outboard motors.

4. Conduct routine inspections

Galvanic corrosion isn’t always visible at first, so make it a habit to inspect key metal components regularly. Look for pitting, discoloration, or white powdery deposits, as these are all early warning signs of corrosion. Once you notice any, it’s best to look for the cause, implement measures to prevent a recurrence and if necessary, replace the damaged components. Interestingly it was routine maintenance that discovered the Statue of Liberty was suffering from galvanic corrosion between the copper exterior and iron supports.

As an additional precaution you can also have a professional surveyor check over the vessel every few years, helping you to identify issues before they become big problems.

The bottom line: Prevention is cheaper than repair

Galvanic corrosion can lead to devastating failures so let’s spark a discussion about it, share knowledge and help sailors of all levels navigate the complexities of life on the water, after all, constructive and respectful conversations make our community stronger.

Selecting compatible metals, using protective barriers, maintaining sacrificial anodes, and performing regular inspections are all viable ways of managing galvanic corrosion, but throwing it out to the community, is there anything you’d suggest to sailors looking to protect their boat from galvanic corrosion?

Share your experiences and tips in the comments to keep this treasure trove of cruising knowledge growing.