Maybe it's time for a rethink on zinc! Not my words, but those of that well known manufacturer of anodes MG DUFF who, of course, are proud to manufacture in the UK! With the emphasis these days on 'saving the planet' most folks will now acknowledge that we are at last slowly moving towards more environmentally friendly products, or cutting right back on our use of plastics. Back in Tynemouth Jenny is particularly proud, or smug if that is the correct word to use, that some 12 years ago when we last changed our car we, or was it she, ignored the advice of politicians and went back down the petrol route. After a couple of issues with our wheels last year (during our drive down to the cruising grounds of Corfu, driving not flying) we decided, for this year, to purchase an almost new, same make same size second hand estate car, once again with a petrol engine..... which we then discovered were almost as rare as hen's teeth but that's another story!
Zinc vs Aluminium, they look the same but which is better? Maybe it's a time for a rethink on zinc, as anodes made from this metal can only be used in salt water whilst aluminium can be used in salt and brackish water. The zinc anode has been traditionally used for over 60 years by boatowners worldwide however more and more aluminium ones are now being fitted as standard by leading UK boat builders! Whilst zinc anodes are widely available for all installations* aluminium anodes, which are available for most applications, have a 20% longer life (think sail drive and out drives that eat up traditional anodes at a fearsome rate.) Other advantages of aluminium anodes include a higher output = better protection and they are three times lighter than zinc, you keen racers will be pleased to note. They even cost less than zinc and of course they are more environmentally friendly.
In Everett Collier's excellent book 'The Boatowners Guide to Corrosion,' in the Appendix or Glossary he describes an anode as 'The electrode of an electrochemical cell with the more negative or less noble potential. The less noble metal of an electrolytic cell that tends to corrode' So the question that is often asked is that 'how come an aluminium anode can protect a sail or out drive which is manufactured from the 'same' metal?' The answer is that your or my unit is manufactured from a very corrosion resistant alloy whilst the anode is not!
A word of caution however, under no circumstances fit a zinc pear shape hull anode ('cos you already have one as a spare) then go out and purchase an aluminium anode for fitting to the prop shaft, out drive or sail drive! Zinc and aluminium should never be mixed.
* Regrettably the Beneteau prop anodes are not available in aluminium, apparently they are too costly to make in this material!