Singing Propeller

[ponapay]

Since recently having changed my engine and fitting a new propeller I have noticed that there is a loud medium high pitched noise emanating from the rear end of the boat.

I assumed it was wind in a hole in the mizzen boom but have recently traced the source. It comes from the stopped propeller at speeds over 4.5 knots, this has been proved through allowing it to trail (no noise) stop (lots of noise) and trail again (no noise).

I assume that it reaches a resonant frequency at 4.5 knots (which continues to at least 8.5 knots - haven't been any faster). Will it damage the propeller? Will it cause a fatigue failure? hat can I do about it?

Any help gratefully received.

ponapay

 

[ccscott49]

It might not be the actual propellor, mine makes a funny high pitched squeak! I've found this eminates from the internal cutlass bearing, squeaking because it's getting no cooling/lubricating water from the engine. If you can, lock the prop, it's better for sailing anyway, less drag.

 

[ponapay]

Thanks, yes that is what I normally do - lock the prop. That is when the singing starts!

 

[ccscott49]

Sorry! Misread it! Shouldn't do any harm, apart from driving you scatty! You say its a new prop, I wondered at first whether it had a little nick in it, causing tip turbulence. But if it's new maybe not. Don't really know what to suggest, now.

 

[boomer]

'Singing' sometimes occurs with motoboat props (and only at certain speeds) so may apply to sailyboats too. The most common cause is that the blades of the propellor have been finished with a square edge. The cure is to create a very slight chamfer called, would you believe it, an anti-singing edge! Best done by a prop expert as the the amount to grind, the angle and the consistency of the chamfer is pretty crucial, as is ensuring that the prop remains balanced. Not an expensive operation, though. Hope this helps.

 

[vyv_cox]

It can also be the opposite - the prop has been finished to a sharp trailing edge. Filing a small flat will remove the singing. The one I put on mine was no more than 1-2 mm wide, no effect on performance that I could detect. This is quite a well-known phenomenon in many flow-related applications, like rudders, sail- and surf-boards, skegs, skis. Seems to be something like vortex-shedding.

 

[ccscott49]

Uuuuuuu.... VyV! Vortex-shedding!! is thast a bit like garden-shedding! Where we all go down to the garden shed with a case of beer and get vortexed!

 

[ponapay]

It appears to have been filed sharp at the leading edge. Should I perhaps try flattening that. or is it best left to the experts?

The boat will be back at the yard that fitted it this winter, I will see if they have any ideas.

Many thanks to all who replied.

ponapay

 

[vyv_cox]

No experience of that one. I don't believe a small flat will have any effect on performance, but I'm not offering any guarantees!

 

[Aja]

My prop 'sings' when at low to medium revs - engine on and in gear - not freewheeling. Is this what you mean? It is a two blade Radicce with fairly square tips and only 3 seasons old.

Always wondered what this was and if it was doing any harm. Always make sure I nudge the throttle up until it stops - luckily at cruising revs.

Donald

 

[Caronia]

I am in the process of buying a Nicholson 38 and wish to avoid extraneous whistling/singing, please advise type of engine/prop size.

 

[ponapay]

Mine only sings when sailing, engine off and shaft locked.

3 blade 17x13, new last year.

 

[ponapay]

Mines a Nic 38 with a new Volvo TMD22P, with (I think) a 17x13 propeller.

I get 6.5 knots at 2300 revs and the boat handles much better astern than ever before.

If getting new engine suggest go out of UK, we saved £2500 by changing it in Denmark (and the VAT rate there is 25%).

If you want to discuss more do e-mail me.

ponapay

 

[Aja]

I'm now wondering if the singing - or 'whineing' to be more exact is a resonance problem lying in the transmission. As I said it is only heard over a band of revs (say 1000 - 1500 revs) - at tickover (in gear) and at normal cruising revs (about 2500) its absolutely fine.

Anyone got this problem?

Donald

 

[brian_neale]

I have a heavy long-keeler with a biggish 3-blade prop, and get a similar effect (Ok at low revs or cruising, whistles/whines in between). The builder told me that it was cavitation, and in practice it is not an issue as I do not spend much time at those revs. Can be a nuisance if motor-sailing, though. Come lift-out time I shall take a look at sharp/square edges on blades and decide then whether to blunt/sharpen them!

 

[Aja]

Dont know if I would need to go to that extent. It only happens within a small rev band. Think I'll live with it

 

[jacksaid]

my fairly new boat wilth Volvo sail drive has similar phenonomen. At around 1500-2200 revs there is a rather load "singing" A small adjustment, up or down to revs and it disappears. I was told by a Volvo marine engineer that this is caused by the trailing edge of the prop and that my prop was probably not a volvo supplied item. Accoding to him the problem does not occur with Volvo props. He said it was fairly common with production boats such as Bavarias where a cheaper prop has been supplied. Apparently no damage is caused by the singing.