Yachting and Boating World forums: Anode placement

the first question is why and the second is what is it to protect. The Cobra 850 is hardly a new boat so what has been fitted before?

Assuming you do have a need to protect the stern gear then It may just be possible to fit a slim collar type. This page from MG Duff discusses the selection of anodes for different environments and This pageshows the types of shaft anode available I am not sure if a suitable anode is available in aluminium though. Shifting between salt and fresh or brackish water is a problem when it comes to choosing the anode material as the link will explain to you.
The closer it is to the prop the faster it will be consumed and if it touches the prop then it will be eaten away locally even faster. (somewhere on the MGDuff website i think there is a recommended minimum distance for the spacing of the anode from the prop but I cannot find it this morning. Maybe it is on another site.

An anode combined with the prop nut as suggested may be a possibility but it will be smallish and may require frequent replacement.

It is well worth looking at the MGDuff website in general.

The more satisfactory solution could be a hull anode fitted as close as possible to the prop but it will have to be wired to the engine/gear box and any flexible coupling will have to be bridged to complete the electrical connection. If the corrosion of your stern gear is truly excessive then an electro eliminator, a system of brushes, to make contact with the shaft may be more effective. You will find them on the MGDuff site as well.

I still ask however if cathodic protection is really necessary especially being moored in water with a low salinity.

Although i have made several links to the MGDuff site I suggest you also look at others and compare what is available from them and their prices

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