Prop whine

[CJU]

I have just fitted a 17x11 3 bladed prop and have found that between 1,000 and 2,500 rpm there is quite a loud whine, it seems OK outside of these revs. I think the noise is also there when the prop is wind milling under sail but is not so loud. I have yet to try it astern or while moored up.

The yacht was fitted with 16x11, which was undersize but whine freee. It is also fitted with an Ambassador rope cutter and the new prop has been modified to accommodate this.

Has anyone any suggestions as to the cause? People have suggested various reasons:

Prop out of balance-I would have thought this would result in more vibration.

Cavitation-not sure about this.

Water flow over the prop and nut-the fairing of the nut to prop boss is not good but I have no idea what effect poor flow would have.
The rope cutter-I have asked Ambassador about the problem and they have never come across it before. They think any faults with the cutter would result in clicking rather than whining.

Engine/saildrive-I contacted Barrus who hadn't come across this before but suggested it maybe due to cavitation.

Sillette props thought it maybe 'prop sing' and a possible cure would be to chamfer a 45deg angle on the aft facing, trailing edge, from the tip to 2/3rds down to the root. This seems a likely cause but I am reluctant to apply the cure, as it means repainting the prop before the tide comes in.


I wondered whether it will resolve itself in time but I am not sure what damage it maybe doing. Not to mention how uncomfortable it is under power.

 

[martinriches]

Could be 'prop sing'.I had this problem last year when I fitted a new shaft. It was in approximately the rev. range you mention. I had the prop ground while I waited by T Norris marine which solved the problem. I would imagine it is a distinctive sound and someone with experience could tell you defiantly .Anyway good luck.

Martin

 

[boatmike]

Yes I agree and Sillette probably have the answer. It's actually an indication that your prop is in good balance and the very slight hydrodynamic disturbance that always exists at the trailing edge of a prop blade is at the same frequency on each blade. At a certain revs this causes the prop to resonate at its natural frequency like ringing a bell. The answer is as they suggested, but don't attack it with a big [--word removed--] file. just a small chamfer will do!

p.s Note to Dan A big rough file IS called a [--word removed--] and it's not rude!!!

 

[Scotty_Tradewind]

yes, I asked my very 'straight' but lovely wife to pass a file last year and I did pause before I suggested the file was of unknown parentage.

 

[Saltram31]

I too have a singing prop. Mine only occurrs when motoring through fresh water.(caley canal) and not in salt water.
I suppose a singing prop is a happy prop. /forums/images/graemlins/grin.gif

 

[CJU]

Thanks for your input, it seems as if the most likely cause is prop sing. All I have to do now is chamfer its edges, lets hope that shuts it up.

 

[Channel Sailor]

I have had a similar problem. Polishing the prop made it worse. I fixed it by bolting a weight (shaft anode) on the shaft inside the boat. Try it in different loactaions to tune out the singing noise.

 

[TheBoatman]

Wht not ring Norris's and speak to Jonathon Norris ~ when it comes to props he's an expert. What he will probably tell you is to grind/file the back or trailing edge of your prop, but under no circumtances touch the leading edge.

Peter.