Propeller Corrosion

[Stemar]

My present prop is a couple of years old and, on cleaning it, it's apparent that there are patches of copper colour on the surface. My previous prop had to be replaced because it had dezincified to the point where it sounded dull when tapped, but I didn't worry too much as it had been on the boat for over 10 years and was second hand when I got it.

Obviously, I'm now concerned that the new one is going the same way. There's always been a shaft anode less than an inch from the prop, changed when it gets tired, but what else could I do?​

 

[vyv_cox]

The effectiveness of an anode is very limited when it comes to preventing dezincification. You are almost, but not quite, trying to protect zinc with zinc, which clearly makes little sense. The zinc lost from brass is actually a zinc-rich phase so it's not quite so simple, but the voltage between the two must be very low indeed. Painting is a far more effective method. Hammerite Special Metals primer adheres very well to brass, I use it under Velox but you could use anything you like.

Your shaft anode is protecting the galvanic corrosion between the prop and the shaft, plus maybe similar couples between blades and pins in a folding or feathering prop.

 

[Stemar]

Thanks for that. I can feel a Velox treatment coming on.