Marina electrics and stray current: the corrosion nobody budgets for

A boat on a Victorian marina berth lost its bow thruster to corrosion — not over years, but months. The repair ran to roughly forty thousand dollars. The cause wasn't the thruster, the anodes, or the owner: it was electricity leaking through the water from somewhere nearby. That's stray current, and it's the corrosion story marinas don't put in the brochure.

Galvanic vs stray current — know which enemy you have

Galvanic corrosion is the slow, predictable one: dissimilar metals in seawater form a battery and the anode pays the bill. Stray current is different — an external voltage (a neighbour's faulty charger, a miswired pedestal, your own bilge pump chafing) drives current through the water and eats metal at wholesale speed. Anodes sized for galvanic duty vanish in weeks; fittings pit; thrusters die.

Why marina berths are the hot zone

• Shore power ties every boat on the dock into one electrical neighbourhood — your protection is only as good as the worst wiring on the pier.
• Warning signs: anodes fizzing or vanishing in weeks, paint blistering around fittings, a tingle from metalwork, pink-tinged bronze.
• An isolation transformer is the gold-standard defence for a shore-powered boat; a galvanic isolator is the minimum.
• Unplug when you don't need the charge — the simplest mitigation of all.

Monitoring beats guessing

The maddening thing about stray current is that you can't see it — until you can see the damage. That's the case for measurement: the Queenscliff workshop runs a corrosion-testing service (reference-electrode survey of your hull potential at the berth), and IonGuard turns the anode itself into a gauge you can read from inside the boat, any day, afloat. The bow-thruster boat would have seen the anomaly months early.

If your anodes are disappearing fast, don't just fit bigger anodes — that's treating the fuel gauge instead of the leak. Measure first. It's a phone call.