[C320-list] Strange Prop Shaft Noise.

[Ian Neale]

Hi,

I have a very strange issue with my prop, prop shaft, or transmission. 

Today we took the boat out after getting the hull cleaned for the sailing season in NZ. 

We motored out for 30 or 40 mins everything seemed normal. We then sailed and per normal had the transmission in neutral with the prop spinning and rather than the normal spinning  sound of the prop and shaft there was a rotational droning noise and accompanying vibration that seemed to align at least somewhat with the rotational speed of the shaft. It felt a little like what imagine a short line caught it the prop slapping the hull. It wasn’t a line though as we were able to replicate the noise after diving the boat to check for something caught in the prop. 

The boat is now on the hard, the shaft seems to not be bent or out of alignment, The cutlass bearing is only 18 months old and seems fine, if a bit gritty when spinning the shaft, there was a small amount of play in the prop, maybe a 1mm at the blade tip. 

Any ideas or similar experiences?  Could it be the prop play, it seems hard to imaging it causing an issue when sailing but not under propulsion, although when motoring the prop would be forced onto the shaft taper. 

Thanks for any insight, Ian Neale. 

Solutions. 1122.

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