I was interested to read your article on “Babs” gearbox. As you probably know, most aluminium alloys, except those containing copper, have a very good corrosion resistance against sea water and will last well in excess of 20 years with little attack.
However, when aluminium is attached to steel or copper or any other more cathodic metal in an electrolyte, i.e. sea water, soil etc. it will corrode “sacrificially” and protect the other metal.
In fact this “cathodic protection” is used for this purpose. Perhaps your boat-owning readers might be interested in the fact that aluminium anodes specially developed for protection of steel and aluminium hulled vessels are available from R. K. L. Alloys, Kings Norton, Birmingham.
Incidentally small anodes were produced not long ago for fixing under the mudguards of cars to prevent rusting. These would of course only be effective when an electrolyte was present i.e. salt water during the winter.
D. F. Fletcher.