All boats from commercial fishing vessels to luxury yachts face a constant threat from corrosion. Galvanic corrosion in particular is notorious for its ability to eat away at metal components, causing significant damage and leading to costly repairs.
In this article I'm going to delve into the basics of galvanic corrosion on boats, exploring some of the causes, effects, and most importantly, how to prevent it.
What is galvanic corrosion?
Galvanic corrosion occurs when two dissimilar metals come into contact and are exposed to an electrolyte. One metal acts as an anode, meaning it corrodes, while the other acts as a cathode, remaining protected. The flow of electrons from anode to the cathode through the electrolyte is what leads to the deterioration of the anodic metal.
Salt water is an electrolyte so it's not hard for galvanic corrosion to occur marine environments. As a result, it's something to understand if you want to prevent damage to your boat or liveaboard yacht.
Cause of galvanic corrosion on boats
Boats are composed of various metals like aluminum, stainless steel, bronze, and zinc, and often these metals touch. Without a barrier between the two, galvanic corrosion can occur.
On a sailboat the most common cause of galvanic corrosion I've seen is when stainless steel comes into contact with aluminum.
Stainless steel fixings being used to hold aluminum framed solar panels
Aluminum rivets or fixings into a stainless steel frame or solar arch
Stainless steel rivets, bolts or mounts on an aluminum mast
Stainless steel fittings contacting an aluminum hull
Stainless steel bolts used to hold aluminum trampoline buttons on catamarans
Over time the aluminum, which is sacrificial to the stainless steel, corrodes and powders away.
Stray electrical current
Often put into the same category as galvanic corrosion is stray current, or electrolytic, corrosion.
Electrical systems onboard, such as faulty shore power connections or improperly installed wiring, can inadvertently create galvanic cells which accelerate corrosion. If you were to have a stray current aboard your boat, you may notice the aluminum anodes below the waterline corroding much faster than expected. This is because the electrical current is acerbating the corrosive reaction of the anode immersed in salt water.
Stray current corrosion can also occur on your vessel when another boat or building nearby has a stray voltage leaking into the water, but it is uncommon.
The negative impact of galvanic corrosion
Galvanic corrosion can have severe repercussions for boat owners if left unresolved.
Irreparable damage to critical components like the hulls, props, hatches, through-hulls and mast, which can impact the structural integrity of the vessel.
Corrosion on the props and shafts can lead to decreased speed and maneuverability, impacting the boat's performance and fuel efficiency.
Expensive repair or replacement bills for parts that have corroded, including anodes, hatches, solar panels and structural components like the mast.
How to prevent galvanic corrosion
Galvanic corrosion can be prevented with the right precautions. To help safeguard your boat, here's what you can do to reduce the risk.
1. Select compatible metals
Before adding or replacing any hardware on your boat consider the type of metal. Ideally you want to pair similar metals, for example putting aluminum rivets through an aluminum mast rather than stainless steel.
2. Create protective barriers
If you must use different metals together, take measures to prevent electrical contact between them. Personally we favor Tef-Gel and Duralac, a well as using gaskets, rubber and plastic spacers.
3. Use sacrificial anodes
Zinc, magnesium, or aluminum anodes serve as sacrificial metals, corroding first to protect more valuable components. Checking and replacing these anodes regularly is essential, particularly for crucial parts like outboard motors and sail drives.
4. Inspect your boat
Galvanic corrosion isn’t always immediately visible, so routine checks of key metal parts are essential. Be on the lookout for pitting, discoloration, or a chalky white residue as these are all early indicators of corrosion. If you spot any of these signs, find the underlying cause, take steps to prevent further damage, and replace affected parts if necessary.
Be corrosion aware
Galvanic corrosion can pose a significant threat to your boat, but with proper understanding and preventive measures its impact can be mitigated. As an owner it's best to be proactive and implement corrosion control strategies to prevent issues before they become a problem.
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