Prop singing

[PaulD]

Had a new 17 x 11 prop fitted a week ago when the boat was in for blacking. Also had a new cup fitted to the skeg.

First trip out today and the prop howls between 1200 and 1400 rpm (engine speed). It is so loud it is unbelievable.

Old prop was 17 x 12 which was a little bit over propped, and had a couple of dings but was completely quiet. I now wish I had never changed it.

 

Any suggestions apart from a new prop?

[Ray T]

Doesn't help, but does it sing this song?

 

 

[pearley]

We had a singing prop after it was changed. Vetus sent me instructions in where to attack the edges with a file. With clear enough water you can do it through the weedhatch. 

 

Can't find the Vetus instructions now but this should help.

 

https://nbsg.wordpress.com/2016/11/05/blacking-and-no-more-singing/

 

At the time I was told the old fashioned remedy was to reverse over a shingle bank!

 

 

 

Edited June 12, 2022 by pearley

[nicknorman]

Yes you just need to blunt the trailing edge of the blades with an angle grinder. I’m sure you could file it through the weed hatch but it would be a horrible job. Best to take it back to where the prop was fitted and ask them to sort it.

[Scholar Gypsy]

1 hour ago, pearley said:

We had a singing prop after it was changed. Vetus sent me instructions in where to attack the edges with a file. With clear enough water you can do it through the weedhatch. 

 

Can't find the Vetus instructions now but this should help.

 

https://nbsg.wordpress.com/2016/11/05/blacking-and-no-more-singing/

 

At the time I was told the old fashioned remedy was to reverse over a shingle bank!

 

 

 

You beat me to it !!

[pearley]

15 hours ago, nicknorman said:

Yes you just need to blunt the trailing edge of the blades with an angle grinder. I’m sure you could file it through the weed hatch but it would be a horrible job. Best to take it back to where the prop was fitted and ask them to sort it.

Wasn't that bad a job. I waited until we were on the upper part of the Weaver so the clear water meant I could see what I was doing. Nice new file and about a hours filing. Weed hatch back on and try it. Some noise still there but better. Weedhatch off again and another 30 mins or so with the file and all good.

[Awayonmyboat]

Whilst filing the edge of the propeller might sound a bit like a bodge, it is not. It is commonly done on even large ship propellers which have unexpectedly shown a singing problem. All good propeller textbooks describe this technique since propeller and hull interaction remains an inexact science. I personally have organised it's implementation on several vessels.

 

In a perfect world I would aim for a flat surface  about 2-3mm wide angled at about 45degrees on the trailing edge from blade tip down to about 2/3 way to the hub, but in reality the detail is not likely to be critical - just try and keep it consistent between each blade. And as said above, if it only partially addresses the problem, increase the width slightly.

 

Good luck.

[PaulD]

Thanks for the advice. Turning into a warranty claim and probably will change the prop.

[IanM]

1 hour ago, PaulD said:

Thanks for the advice. Turning into a warranty claim and probably will change the prop.

 

What will you do when the next one inevitably does the same?

 

Just take an angle grinder to it.

 

Edited June 14, 2022 by IanM

[PaulD]

3 hours ago, IanM said:

 

What will you do when the next one inevitably does the same?

 

Just take an angle grinder to it.

 

How common is this problem ? Why don’t the prop builders test them in a tank or something ?

[Cheshire cat]

I on't think its that simple. It depends on fluid dynamics and where the prop is in relation to the various other bits of metal around it, Each boat is unique in that respect. I think it also depends on how much metal there is in the prop and when harmonics kick in.

[Alway Swilby]

I think it is a common thing. Our brand new boat did it on its first test run out of the boat yard. They were able to pull the stern out of the water on their slipway and angle grind the edges of the prop. Worked a treat and still working like a treat 5 years later.

[cuthound]

On 14/06/2022 at 17:15, Alway Swilby said:

I think it is a common thing. Our brand new boat did it on its first test run out of the boat yard. They were able to pull the stern out of the water on their slipway and angle grind the edges of the prop. Worked a treat and still working like a treat 5 years later.

 

Same happened with our second shareboat.

 

Five minutes on the slipway with an angle grinder cured it.

 

No issues with the prop on the firdt shareboat, or with the bigger prop fitted to my current bost, so on a very small sample, maybe 1 in 3 sing.

[Peter Duddigan]

Our prop is a four bladed 21x18 originally from a sea going trawler. It only travels at 300rpm so have no idea if would sing or not at high speed. Reading about your dilemma, it's a new one on me. I had no idea this do at tbof problem occurred. Do aircraft have a similar problem I wonder?

[BEngo]

Yes.  Not so much in  prop driven fixed wing aircraft, but rotor blade vibration generally can be a significant problem in helicopter main  and tail rotor blade design. Normally it has been fixed before the aircraft are in service though.

 

N

[Peter Duddigan]

I have heard of problems with helicopter props

[ditchcrawler]

16 minutes ago, Peter Duddigan said:

I have heard of problems with helicopter props

Where's @nicknorman

Edited June 19, 2022 by ditchcrawler

[BEngo]

55 minutes ago, Peter Duddigan said:

I have heard of problems with helicopter props

Helicopters as a breed suffer from vibration.  Once past the design stage, it is usually the airframe and contents vibrating in response to the fan on the roof, or the one at the back, going about its business.    Each blade passing the tail boom of the helicopter generates a force on the boom and so shakes the airframe up and down as wels as sideways. Some things in the aircraft then react to that shaking and rattle around themselves.  Sometimes this is deliberate.  Sikorsky used the main battery of the S61 as a vibration absorber.  Sometimes it was not.  The Westland Lynx used to shake the engines so much that the mounting bearings wore out quite quickly.

 

There are all sorts of tricks to reduce, but never eliminate entirely, helicopter vibration.  Balancing the main and tail rotor blades, and getting them all to fly in the same plane is the starting point. There are lots of engineering dissertations on the subject should you ever suffer from insomnia!

 

N

 

[ditchcrawler]

They dont do a hangover much good but the shaking use to send me almost instantly to sleep,