Earthing strap

[Topcat47]

I have a long keeled yacht with not enough room to put an anode on the exposed length of prop shaft. For years I had an earthing strap around the plastic flexible coupling. I don't know who made it but it lasted for ages. Since it failed, however, I have had trouble trying to keep a strap whole for a single season. i have had them made up with copper mesh, 6mm copper wire and even a copper strip but they just fracture. The last one has failed after a couple of months.

I know the shaft and prop are dissimilar metals, but how important is it to link the prop and shaft to the hull anode in this way. My hull anodes are not badly corroded over a year. Even the little thing in my Yanmar lasts that long and I do haul out once a year to do the underwater maintenance anyway.

 

[pvb]

MG Duff make a thing called the Electro Eliminator, which is a pair of brushes on a bracket. The brushes rub on the propshaft and a cable connects them to the hull anode.

 

[Pye_End]

I know the shaft and prop are dissimilar metals, but how important is it to link the prop and shaft to the hull anode in this way.

Probably important, and unless you want a new prop you may not want to find out how much effect it is having.

I had similar problems, and eventualy settled on beefy wire (maybe battery cable 15mm2) with big crimp at one end, and the other end jubilee clipped onto the shaft, with another clip to help keep the wire tight to the shaft. When the previous version broke the shaft anode was not connected for probably a few months and the prop came out pink and bubbly, and now has some pitting. Similar to you, my hull anode lasts for a long time.

 

[vyv_cox]

Pure copper, such as would be selected for electrical purposes, has very poor mechanical properties. It might be worth sacrificing a little electrical conductivity in exchange for strength, by using brass. Sheet brass is usually 70/30, which would be easy to form and a lot stronger than copper.