Marine Bonding and Galvanic Isolator Installation
Underwater metals on a boat corrode faster when the wrong currents flow between them. Marine bonding, sacrificial anodes and a galvanic isolator on the shore power earth are the electrical defences. We check, repair and install bonding systems and galvanic isolators, and give a written quote before work starts.
Galvanic corrosion happens when different metals sit in seawater and are electrically connected: the less noble metal gives itself up to protect the other. Anodes are fitted to be that sacrificial metal. Bonding links the underwater fittings so the anodes protect them all. Stray current corrosion is different and often faster, caused by current leaking from a fault on board or arriving through the shore power earth.
People often call it boat electrolysis. Whatever the name, the signs are anodes wasting unusually fast, pitted props and shafts, or pink, weakened bronze on seacocks.
Checking an existing bonding system
A bonding system only works if every connection is sound. Bonding wires corrode at their terminals in the bilge, get disturbed during other work or are left off when fittings are replaced. We trace and test each bond with the boat ashore or afloat, check continuity to the anodes and look for current leaking from the DC system that could be driving corrosion.
- Continuity from each fitting to the anode
- Condition of bonding cable and terminals
- DC leakage checks on the main circuits
- Shore power earth arrangement
Galvanic isolator installation
When a boat is plugged into shore power, its earth is linked to every other boat on the pontoon and to the marina's earth. That creates a path for galvanic currents that can eat anodes in weeks. A galvanic isolator fitted in the shore power earth line blocks those small voltages while still allowing fault current to flow, so the safety earth keeps working. It is fitted close to the inlet, sized to the shore supply, and tested afterwards.
Isolation transformers
An isolation transformer separates the boat's AC system from shore completely, with no direct earth connection between them. It gives the most complete protection but is larger, heavier and more expensive than an isolator, so it suits boats that spend long periods on shore power or have higher AC loads. We will talk through which suits your boat.
Fitting bonding during other work
Bonding is easiest to put right when the boat is out of the water and the bilge is open, alongside a rewire, new seacocks or a shaft and prop change. If the yard is replacing underwater fittings, the electrical bonding can be reconnected and tested at the same time. Our guide to marine bonding systems explains the principles in more depth.
Marine bonding systems explained · Galvanic corrosion and isolation
Frequently asked questions
Do I need a galvanic isolator on my boat?
If the boat uses shore power and has metal underwater fittings, a galvanic isolator is a sensible protection against galvanic current arriving through the shore earth.
What size galvanic isolator do I need?
It is sized to the shore power supply and the fault current it must carry. We match it to the inlet and supply on your boat.
Do galvanic isolators go bad?
They can fail, particularly after a fault or lightning. They should be tested periodically, and some models include a status indicator.
What is a galvanic isolation transformer?
It is a transformer that separates the boat's AC supply from shore with no direct earth link, giving full isolation from shore-side galvanic currents.
What is galvanic isolation in an inverter?
Some inverter-chargers isolate the AC output from the input electrically. It is not the same as a galvanic isolator in the shore earth, so the shore power earth still needs considering.
Get your bonding checked
Tell us what you are seeing on the anodes or fittings, and where the boat is kept, and we will arrange a visit and written quote.