Electrolysis & Galvanic Corrosion.
Ignoring your boat in the marina is like ignoring the missus … next thing you know, she’s quietly corroding… and planning your financial ruin!
Electrolysis and Galvanic Corrosion : Don’t Let It Sneak Up On You
With winter haul-outs underway, we’ve spotted a couple of key things many marina boat owners don’t realise until it’s too late.
We advise you do a Galvanic Test Before Haul-Out
This test must be done while your boat is still floating. It will show up any problems you may have with stray current due to poor connections, dodgy electronics or faulty wiring etc…. The test will give you peace of mind of that your galvanic protection is functioning correctly.
We see it all the time, boats come out of the water, and then discover the anodes and underwater gear are looking a bit dodgy. But it’s too late to test for stray current once you’re up on the hard. So please remember to take the time to do this test while your boat is still on her marina, before you haul out.
What Is Galvanic Corrosion and Electrolysis?
OK, so I questioned the tech team about this and within minutes we were down a complicated technical wormhole. There is a lot of tech around this topic, so I have tried to distill - to all you actually need to know. If you want more about the technical process and testing talk directly with one of our team, or go on you-tube (it’s a great cure for insomnia !).
In the meantime this is what you need to know:
Galvanic corrosion happens when two different metals are sitting in saltwater (a good electrical conductor). An electrical circuit is created, and the more reactive metal (called the anode) starts to corrode to protect the less reactive metal (cathode). This is a normal, natural process and it is why we use sacrificial anodes, like zinc or aluminium on your boat’s hull. They are designed to wear away before any of the important bits do.
In normal saltwater conditions, your anodes should last about 18 - 24 months.
Electrolytic Corrosion (also known as stray current corrosion) happens when there is stray electrical current leaking into the water, it causes the corrosion process to speed up considerably. The signs are the same as the natural galvanic corrosion, only the anodes will disappear a lot faster, leaving your rudders, shafts, propellors etc … very vulnerable. Because the damage can happen so quickly, we recommend an annual ‘galvanic test’ for your peace of mind, but we also recommend for you to keep a bit of an eye on your anodes or for signs of corrosion. If they are deteriorating quickly, please get in touch with us asap.
What does a Galvanic Test Do?
It tests for stray electrical current around your boat, which is why it must be done while she’s still in the water. It tests all your galvanic protection is working correctly. If it shows everything is good, happy days your boat is safe and if it detects a problem it can be remedied for you have a big expensive problem.
Stray current could be coming from:
Your own boat (wiring faults, poor bonding, faulty electronics), this could be through poor installation or just something that happens over time.
Your shore power connections
Or occasionally other nearby sources.
Anodes are the Unsung Heroes
Those crusty metal lumps on your hull? They're the real MVPs. (most valuably players)
Anodes are designed to sacrifice themselves to protect your underwater gear. Ideally, they should be about 50% worn after 12 months. If they’re vanishing faster than that, you’ve likely got a electrolysis issue.
What you can do to keep your boat safe from galvanic and electrolytic corrosion.
If Your Boat Lives in the Marina schedule an annual in-water galvanic test
It’s one of the smartest preventative maintenance steps you can take. It’ll check you protection is working correctly and pick up any stray current that could cause electrolytic corrosion issues. The test could save you a heap of hassle (and a big repair bill) later.
Check your anodes regularly.
Always keep an eye on your anodes, those‘MVPs’, if they are looking a bit worn change them out. Easiest way to check is to pop on a mask and snorkel, but not in the marina, there maybe stray current around (never swim in the marina). We are always available also to pop down and check for you if you are worried.
If you see signs of early wear on your anodes ?
If they’re new and already looking rough, book a galvanic test, it’s most likely a bonding or wiring issue that can be easily remedied.
Don’t mix anode types.
Stick to one metal type (zinc or aluminium) and one brand. Mixing them is like putting diesel in a petrol ute… just don’t.
Shore Power + Galvanic Isolator = Essential
If your boat’s plugged into marina shore power, a galvanic isolator is a must-have. If you don’t have one, we recommend having one installed as soon as possible. They need to be installed by a registered marine electrician, so speak with us.
The galvanic isolated is fitted between your shore power earth and your onboard AC system. Its job is to block low-voltage DC current that causes electrolytic corrosion, while still allowing AC to flow for safety.
⚠️ Weirdly, a galvanic isolator isn’t required for EWOF, but it must be fail-safe rated if installed. It should always be fitted by a Registered Marine Electrician, so talk to the team at HMB Marine Electrical.
Why Install One?
Stops corrosion from stray electrical currents
Protects your props, stern legs, and through-hulls
Reduces the frequency of anode replacement
Saves serious $$$ in long-term repairs
Not sure if yours is working, or if you even have one? Have a chat with us we can take a look.
Trailer Boats / outboards - You’re Not Off the Hook completely
Trailer boats are at less risk but still vulnerable, especially if:-
They sit in saltwater for long periods
They’re plugged into shore power
You have an aluminium hull, even stored boats can corrode if saltwater is left in the bilge and reacts with loose bits of metal (like screws or coins).
Trailer Boat Corrosion Prevention Tips:-
Keep the bilge dry and clear of loose metal
Wash down with fresh water after saltwater use (Salt-Away helps!)
Use the correct manufacturer anodes for your outboard !!
Never mix anode metals.
Saltwater vs Freshwater Boats
Saltwater is highly conductive. This means corrosion happens faster. Use zinc or aluminium anodes or recommended manufacturer anodes
Freshwater is less conductive. Corrosion happens more slowly, but can still happen. Different anodes are used for fresh water and are usually either aluminium or magnesium.
Quick Summary
Get a galvanic test before haul-out
Check and replace anodes regularly
Don’t mix anode types
Install a galvanic isolator if you use shore power
Call us if you’re unsure or want to arrange a galvanic test - we’ll sort it out