Cavitation resonance

[FrankieJ]

On our Bavaria with a MD22 & saildrive we are experiencing a loud whining sound when the engine reaches 1200 rpm. and it seems to disappear at much higher revs. I think it must be the prop. as it doesn't happen when neutral or when in gear but tied up. I have done a breath holding visual on the prop and it apears to be ok. Could it be some kind of cavitation resonance ?~~~ Any thoughts?~~~

 

[Pye_End]

A singing propellor.

Get the edges of the prop ground off (by a specialist!) and it will go.

 

[kengill]

You need to file the trailing edges of the propellor blades at 45 degrees leaving a chisel edge this will eliminate the singing.

Regards
Ken

 

[NPMR]

Agree with Vitalman - simply take a file to the trailing edge of the prop- and silence will ensue!

Ours cut in at cruising speed and drove us all mad - the previous owner had just put up with it!

It doesn't seem to be critical to get a high shine on the filed area but it feels obvious that a better finish is more appropriate.

 

[FrankieJ]

Which side of the blade do I file the chamfer, the side that's 'pushing the water' or the 'backside' ?

 

[Pye_End]

Get a prop maker to put an 'anti-singing' egde on. It is not a DIY job as the prop will need balancing.

 

[boatmike]

Dissagree. A small chamfer filed equally on each blade will not upset prop balance and is an easy DIY job.