Having just done the antifouling stint, other owners may be interested to hear what we
worked out with an engineering adviser about earthing. The reason there is only a single
pair of anodes, i.e. on the rudder, is that the loom of earthing straps on the boat connects
to the anode pair. I've checked this with a multimeter. It has overcome my concern that
there didn't seem to be any zinc protection for the prop and shaft, nor any room to attach
an anode direct to the shaft.
Whilst the modern advice on galvanic corrosion, especially in marinas, is for each thru-hull
to be separated from the others, clearly every other thing which is attached to the prop
shaft either directly or by liquid, e.g. engine block, fuel tanks, metal parts of the engine
water inlet system, and the outer brass tube of the prop shaft system, needs to be
protected, which I have achieved by checking the integrity of their connections to the
rudder anodes. There is, of course, the small zinc in the heat exchanger but this is tiny,
even if owners do remember to change it.
Regards Roger, Mango 28 Zorba