Galvanic Corrosion

Galvanic Corrosion and Galvanic Isolators

The Galvanic Corrosion Problem:

The use of shore power bonds (earths) your boat via the earth cable (green/yellow) in your shoreline power cable, by tying the hull to the shore earth/grounding system and to other adjacent vessels also connected to shore power. This connection, while required for safety, creates a galvanic corrosion cell involving the dissimilar metals between boats and also between boats and the shore earth including any submerged bonded metalwork in the jetty— as shown in the following diagrams.

Four Components are Needed for Corrosion:
1) Anode – a metal surface which gives up metal ions (corrodes) (In our case the boats hull)
2) Electrolyte – a medium which conducts ionic current between the anode and cathode (The water)

3) Cathode – a metal surface that picks up metal ions (The jetty or another boats hull)
4) Metallic Bond – a continuous metallic path that allows current to flow from cathode to anode (The shore line)

The Solution:

A simple and cheap method which virtually eliminates this galvanic corrosion problem is to insert an appropriately rated and certified Galvanic Isolator in series with the earth cable of the shoreline power cable. The function of the Galvanic Isolator is to provide AC continuity of the grounding conductor (required for safety in the event of an AC fault) and to block the flow of corrosion-causing galvanic current.

Galvanic isolators cost less than a £100.00 are very simple and safe to DIY install and can save your hull from the accelerated corrosion the galvanic action causes, saving you thousands in the cost of hull replating.

Alternatively if you can not afford the cost of a galvanic isolator unplugging your shoreline when the boat is not in use breaks the metallic bond preventing any galvanic action taking place.

Gary Peacock October 2004