Some many years back I discovered that two propellor shaft anodes extended the life that one would have and by more than double.
With luck some savy technical reply will advise me why this is, for now just believe its true!
This 18" Max Prop has been in service around twelve years now, a shaft anode fits just behind it, then a second behind the A bracket and Vesconite bearing.
The paint job is sprayed on Prop O Drev, it will give two years service and require very little in the way of cleaning. The anodes are now fitted prior to the re launch.
Note, use a small hammer to tap the anode onto the shaft, re tighten the screws often as you fit them.
Roy