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galvanic isolator

Just blacked boat and surveyor commented that corrosion was result of electrolytic action. Generally a continuous cruiser, boat has been in marinas for last 2 years for 3 to 4 months but have relied on solar to kep batteries topped up with no shore connection. Is connection necessary for isolator to work or should an eart connection be made to shore?

Asked by: peter osullivan  | 8.47pm, Friday 28 March

WW says:

The galvanic isolator stops electrolytic corrosion to the boat hull from stray electric currents from the earth connection of a shore power connection. Any power generated on board will not produce a current flow off the boat and will not be the source of corrosion.
The majority of corrosion to steel immersed in water is due to electrolytic action, especially with the boat moored in a marina. The boats and other metals in the water (especially galvanised piling) will set up small battery circuits with the canal water (which is not pure, and contains a mixture of various chemicals) forming the electrolyte. The composition of the steel hull of the boat is also not entirely homogenous, with small pockets of slightly differing chemical composition reacting with their surrounding steel via the electrolyte.
This illustrates the fact that a good paint coating of the entire underwater surface of the boat, thus stopping contact between the canal water and the bare steel, is the best way to prevent corrosion.

Rupert Smedley  | 12.31PM, Sunday 30 March

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