17/05/2021 at 10:02 #24043
I think you want a magnesium anode rather than the more usual zinc. They make themy specifically for aluminium rudders as large diameter profiles discs. Ed.2/6/21 This response is incorrect, with apologies, as magnesium is freshwater use only. Large disc zinc anodes should be used.
Available from lots of places. E.g Force 4