They are not particularly expensive but are worth the outlay for the protection that they offer, especially if the vessel spends a lot of time connected to shore power.
New saildrive zinc anode
A more thorough (and expensive) solution is to fit an isolation transformer, which introduces a physical break in all three incoming shore power wires and transfers power onto the boat magnetically via the transformers windings. This can provide a very safe electrical environment for working on the vessel’s electrical systems and for any swimmers in the water as the boat is no longer physically connected to the shore side power circuit. They are also excellent at preventing local stray current corrosion, but that is a subject for a blog in itself.
IN SUMMARY:
Fit the right anodes for your environment “Mountains-Am-Zee”
Buy quality anodes from a reputable source
Fit them according to the vessel type at the recommended scaling
Make sure they are below the water- line but not on the bottom plate
Consider whether the vessel needs bonding
Examine the shore power connection and upgrade it if possible Do not paint anodes or grounding plates
Bronze grounding plate
A final consideration in how to protect the boat from galvanic corrosion is the risk posed to it by other vessels via shore power connections. The earth wire is connected as a common ground for all vessels and the pontoons themselves. There have been many instances of vessels suffering dramatic and, in some cases, terminal corrosion due to the faulty connections of shore power terminals or nearby vessels, which can turn your own hull into one massive anode and wreak havoc
with propshafts, props and if a skin fitting is compromised the vessel is at risk of sinking.
A galvanic isolator (sometimes also referred to as a zinc saver) is fitted into the vessel’s earth wire immediately after the shore power connection socket and before the earth wire connects to the boat electrics in any way. It is a solid- state device which blocks any stray currents and prevents the boat’s anodes being used to protect nearby vessels and the pontoon!
Other reading on this topic The author refers you to an excellent, recently published handy guide which covers this and related matters, co-written by Jeffrery Casciani-Wood HonFIIMS and Elliott Berry FIIMS that is available from the IIMS.
What A Marine Surveyor Needs to Know About Corrosion, Electrolysis, Galvanism, Anodes & MIC is available in paperback at £25 plus post and packaging or as a downloadable pdf for just £22. Click for details at
https://bit.ly/3hVwjxf.
The Report • September 2020 • Issue 93 | 95
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