SURVEY & CORROSION
Corrosion in its many forms
Q During a recent chat at my sailing club questions were discussed about anodes, galvanic corrosion and earthing, sailing in salt water and then into fresh water.As expected, there were many different views and disagreements.
What are the best methods to protect a vessel going from one water type to another and what earthing methods would you recommend?
Could a lightning conductor, as used on tall buildings be of use, either the rod type or the flat plastic-covered type that can be bent to follow the contours and shape of a vessel? Would it also protect against galvanic corrosion?
Bob Williams
Colin Brown replies: It would be easiest to answer your questions with a quick summary of the hows and whys of anodes.
If you connect any two different metals and put them in salt water, they'll create a small but measurable voltage. This can drive electrons from one metal to the other so one metal corrodes preferentially leaving the other metal undamaged.
Metals can be arranged in a hierarchy of potential – a Galvanic Table.stronger the reaction.
