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Long Beach Marine Electric connects boat owners with licensed, insured marine electricians for galvanic corrosion testing and stray current diagnosis: measuring hull potential with a silver/silver chloride reference electrode, finding leakage on board, and installing galvanic isolators or isolation transformers. In a crowded marina, boats are connected to each other through the shore-power safety ground, so a neighbor's problem can eat your zincs. Testing tells you whose problem it is.
What happens on the first visit
- Hull potential readings with a silver/silver chloride reference electrode, with shore power connected and disconnected, to separate a marina-side problem from an on-board one.
- Check of the bonding system: continuity from each underwater metal (shaft, strut, rudder, through-hulls, outdrive) to the anodes.
- Leakage-current test of the boat's DC and AC systems. A small DC leak to a bonded fitting is classic stray-current corrosion.
- Anode condition and type check: zinc, aluminum or magnesium suited to salt water and to your underwater metals.
- A written finding and options: anode changes, bonding repair, a galvanic isolator or an isolation transformer, each with a price.
Galvanic corrosion vs stray current
Galvanic corrosion happens when two different metals are connected and immersed in the same seawater. The less noble metal corrodes to protect the more noble one. That's what sacrificial anodes are for. Connected to shore power, every boat's underwater metal is also tied to every other boat's through the green safety ground, so a dock of boats becomes one big galvanic circuit.
Stray current corrosion is faster and worse: DC current leaking from a wiring fault, on your boat or nearby, leaves through an underwater fitting and takes metal with it. It can destroy anodes, props and outdrive legs in weeks rather than seasons. The symptoms look similar from the dock, so measurement is the only way to tell them apart.
What a reference-electrode test tells you
A silver/silver chloride reference electrode lowered into the water next to the hull measures the boat's corrosion potential in millivolts. The working rule from cathodic-protection practice is that adequate protection shifts a metal's potential at least 200 mV more negative than its natural resting voltage. Aluminum is the special case: it rests around -760 mV in seawater, needs about -900 to -950 mV for protection, and shouldn't be driven past about -1,100 mV, where overprotection blisters paint and damages the metal. That's why an aluminum outdrive needs the right anode, not just more of them.
Taking readings with shore power on and off, and with on-board breakers switched one at a time, shows whether the problem comes in through the shore cord or starts on board.
Galvanic isolator or isolation transformer?
A galvanic isolator sits in the shore-power ground and blocks the low-voltage galvanic currents between boats while still passing fault current to keep the ground safe. A fail-safe, ABYC A-28-compliant unit such as the ProMariner ProSafeFS lists at about $605 before installation. An isolation transformer breaks the direct connection to shore power entirely. It's the stronger fix, also removes the need for an onboard ELCI if mounted within 10 feet of the inlet, and is common on larger yachts, but it's heavier and costs more. Read galvanic isolator vs isolation transformer for the full decision.
Insurance, warranty and who pays
Corrosion testing and isolator installation are owner-paid. Corrosion damage itself is usually treated by insurers as wear, not a covered loss, which is why catching it early with a test is cheaper than replacing an outdrive. Testing typically takes one to two hours at the slip. Anode replacement on shafts and struts waits for a haul-out or a diver.
What's included
- Hull potential readings (shore power on/off)
- Bonding system continuity check
- DC and AC leakage testing
- Anode type and condition assessment
- Galvanic isolator installation
- Isolation transformer assessment
- Bonding repair
- Written readings and recommendations
DIY vs cheap fix vs proper corrosion work
| Factor | DIY | Cheap operator | Proper marine work |
|---|---|---|---|
| Diagnosis | Look at the zincs | Replace zincs | Reference-electrode readings, power on and off |
| Anodes | More is better | Whatever fits | Right metal and size for the readings |
| Bonding | Not checked | Not checked | Continuity verified to every fitting |
| Shore-power path | Ignored | Ignored | Isolator or transformer where needed |
| Result | Zincs gone again | Damage continues | Protected range confirmed by measurement |