Shaft Anode Puzzle

[Gypsyjoss]

Fellow yachtie in this Greek yard has a Discovery (Dromor). Standard GRP, shaft drive with the usual anode bolt clamped to the prop shaft.
It does the job and corrodes OK, but from the inside so that it ends up rattling around the shaft!!!!

Anyone know why this should happen?

Pete

 

[Tranona]

'cos it does! It helps if the shaft anode is exactly the right size (eg 25mm is less than 1", so the latter will be a poor fit on the shaft) and that the two halves are firmly banged together before the bolts are fastened.

 

[Gypsyjoss]

'cos it does! It helps if the shaft anode is exactly the right size (eg 25mm is less than 1", so the latter will be a poor fit on the shaft) and that the two halves are firmly banged together before the bolts are fastened.

Mine doesn't come loose on the shaft, nor anyone ele's that I've spoken to. They corrode on the outside.

 

[vyv_cox]

I suspect it was not fully tightened in the first place. Most of the ones I buy have a steel strap against the shaft, cast into the zinc. It isn't possible for this to corrode away and rattle, assuming it was tight in the first place. As Tranona says the two halves need to be banged together, then tighten the bolts, then bang again. Repeat until the bolts won't turn any more.

 

[theoldsalt]

When I fitted a shaft anode a couple of years ago I tightened the bolts as tight as I could. However half way through the summer there was a very loud banging every time I went astern.

It turned out that the shaft anode had corroded on the inside and come loose on the shaft. The wash from the prop was pushing the anode forward along the shaft until it was hitting the hull.

I haven't fitted a shaft anode since.