Stop Your Boat From Corroding: Victron Galvanic Isolator Explained
Your zincs are doing their job — but they can only do so much. If your boat spends time plugged into a marina dock, there's a corrosion mechanism at work that sacrificial anodes can't fully defend against. A galvanic isolator stops it at the source. Wesley explains the whole picture in the video above.
The Problem: Electrolytic Corrosion from Shore Power
Electrolytic corrosion is a specific, accelerated form of metal degradation that happens when stray electrical current passes through an electrolyte — in this case, seawater. The underwater metals on your boat: propeller, shaft, rudder fittings, through-hulls. Seawater is an excellent conductor. When current flows through it, metal dissolves. Rapidly.
Sacrificial anodes (zincs) provide localized protection by offering themselves as the preferred target for galvanic current. They work for the galvanic corrosion that happens naturally between dissimilar metals on your own boat. But they can't fully defend against what happens at a marina dock.
The Root Cause: Shared Dockside Grounding
When you plug into shore power at a marina, you connect through a three-conductor cord: hot, neutral, and green safety ground. Every boat plugged into the same dock shares the same green grounding conductor. That shared connection creates a massive electrical circuit linking the underwater metals of every vessel on the dock simultaneously. Low-level DC galvanic currents naturally flow between dissimilar metals in this circuit — through seawater.
Your zinc is designed to protect your boat from itself. It's not sized to protect your shaft and prop from the current flowing in from the boat two slips down.
How a Galvanic Isolator Solves It
A galvanic isolator is installed in series with the green safety grounding conductor. It uses diodes to block the low-level DC currents that cause galvanic corrosion, while passing AC fault currents instantly and completely.
That second part is critical: the isolator does not interrupt safety ground protection. If there's an AC fault on your boat, the current passes through the isolator without restriction, your breaker trips, and you're protected. The isolator only blocks the low-level DC that causes corrosion.
ABYC Standard A-28 establishes this specifically: a galvanic isolator is the only device legally permitted to be installed in series with the AC safety grounding conductor on a marine vessel. Victron's galvanic isolators are designed to meet A-28.
Victron's Galvanic Isolator Lineup
| Model | Shore Power | Best For |
|---|---|---|
| Victron VDI-16 | Sub-16A | Small boats, light shore power setups |
| Victron VDI-32 | 30A | Standard single-phase 30A marina pedestals |
| Victron VDI-64 | 50A | Heavy-duty 50A split-phase service |
All three carry an IP67 waterproof rating — designed to live in bilges and engine rooms. Victron backs all three with a 5-year warranty. Selecting the right model is straightforward: match it to your shore power cord amperage.
Galvanic Isolator vs. Isolation Transformer
A galvanic isolator is the most cost-effective solution for most boats — compact, affordable, and it directly addresses the marina dock corrosion problem. An isolation transformer provides complete electrical isolation between shore power and your boat's system for even more comprehensive protection. Wesley covers the isolation transformer separately. For most boats at marina docks, the galvanic isolator is the right starting point.
Installation: What to Know
- Installed on the green safety grounding conductor only — not on hot or neutral
- Must be rated for your shore power amperage
- ABYC A-28 specifies fault current pass-through capacity requirements
- Install as close to the shore power inlet as practical
- Should be done by a qualified marine electrician — an incorrectly installed isolator can create a safety hazard
Browse the full galvanic isolator collection at Blue Marine. If you have questions about which model fits your shore power setup or want help planning the installation, schedule a free consultation with our ABYC-certified team.
Related reading:
Victron Autotransformer vs Isolation Transformer: Which One Do You Need?
The Complete 2026 Boating Guide: New Codes and Standards
12V vs 24V vs 48V Marine Electrical Systems: Which Is Right?
