Unknown prop noise help! beneteau 427

[David 01]

If anybody has any idea of what this noise is?
I was out on a short trip and this noise suddenly developed, I had the boat lifted and looked over by an engineer, no obvious sign of anything, had the cutlass changed as there was play, the dripless changed as it was due anyway, engine aligned and a gearbox flush and service, boat has a max prop classic seemed to be working correctly and greased well, there was a slight chip on one of the blades that I noticed, apart from that in good condition, boat went back in the water and has exact same noise, it comes directly from where the prop is.
Noise happens between 1200rpm and 1800rpm.
Video 1 is just going along at about 1400 rpm.
Vid 2 I am increasing and decreasing the throttle in and out of 1200rpm.
Everyone's baffled and nobody has a clue.

Any help would be massively appreciated.

 

[Refueler]

It sounds more like rubbing ....

Do you have a rope-cutter fitted ? Has it moved or been altered in any way ?

 

[Daedelus]

If the rope cutter has been fitted close to the cutlass bearing then you can get a sort of rumbling noise. It needs to leave a decent water gap and be close to the prop.

 

[SteveG]

If you have an Ambassador scissor action cutter, check the positioning of the fixed blade on the P bracket. If it is spaced too far outwards from the P bracket (adjustable with the 3 grubscrews and lock nuts), it can fould on the caphead bolts holding the rotating parts together. Took me a while to find this too. I was convinced it was cutless brg or stern gland - wrong! Had similar noise from a loose engine monting nut on another occasion. Might be worth checking.

 

[David 01]

thanks for your reply steveG my rope gutter is a single blade one that bolts to the shaft in-between the p bracket and prop, as for the mounts I would of thought the engineers would of gone over the nuts while adjusting the engine but I will have a look at that with a spanner. Thanks.

 

[Halo]

Could it be cavitation around the chip ? How big is the chip? Have you got a pictures?
From memory Some really old threads talked about filing the edges of conventional props to stop similar noises

 

[V1701]

Could it be cavitation around the chip ? How big is the chip? Have you got a pictures?
From memory Some really old threads talked about filing the edges of conventional props to stop similar noises

Isn't the filing the edges of the prop thing when you have a singing prop? My mate had it on his new to him narrowboat, it was so loud I was convinced it was a bone dry stern gland but no...

 

[vyv_cox]

Isn't the filing the edges of the prop thing when you have a singing prop? My mate had it on his new to him narrowboat, it was so loud I was convinced it was a bone dry stern gland but no...

Yes, I first came across this phenomenon when I bought a new Hobie 16 catamaran. At speed the rudders would howl. I filed flats on the trailing edges and subsequently treated several.other boats the same way.

Later I did the same with new yacht propellers, quieting them immediately.

 

[David 01]

My thoughts have been cavitation/singing prop, its the only thing it could be as I've changed everything else, there is a video on utube of a singing prop that sounds pretty much like mine does, probably the chip? It came on quite sudden while motoring home, the chip is about 3mm wide and 2 mm deep, I wish I had taken pictures when it was out of the water but didn't think to

 

[Refueler]

Next time boat lifted - I would be looking at prop overall ... usually when a prop strikes and loses a 'chip' it can turn the edge ...

A quickie way to check prop edges - ALL edges .... is to use a laser / LED line instrument .... builders etc. use them to have a straight line to follow ....

On a tripod - the Laser is set up to shine along the edge of a 'good' blade ... leaving Laser in place - turn prop so next blade is aligned - you will see if blades are turned / same ... if 3 blades - check the next and so on ...
Then do for the other edges .....

Another check is the prop tips ... are they same - trace round on card good tip, also card length is blade length from hub - offer up card to check other tips shape and length to hub.

I do not say that the above can create your sound - but it's worth eliminating ...

3mm x 2mm ... is not much - but if its out at tip - its 'amplified' by its being out at tip .... A temp fix is to use plastic metal to fill and then grind back to shape .... it will not last long - but would indicate if its the chip ...

 

[David 01]

Hi, thanks for the informtion, I was thinking to send the prop off to a specialist when I have her out the water next, for a full checkout, I wish I'd done it when I just had her out, I noticed today when I was out in her that when I turn quite steeply most of the sound drops off, then comes back when I straighten up.

 

[Refueler]

Hi, thanks for the informtion, I was thinking to send the prop off to a specialist when I have her out the water next, for a full checkout, I wish I'd done it when I just had her out, I noticed today when I was out in her that when I turn quite steeply most of the sound drops off, then comes back when I straighten up.

mmmmm interesting .... when you turn the apparent thrust line of the prop alters .... and outer turn blade tends to bit more than the inner turn blade .. this can load the shaft one way or other ... the difference in 'thrust' is small but can be enough ......

But turning sharply will change sound on any prop / shaft / engine anyway ...

How's the rudder stock bearings ??? Any play in the stock ... for this you'd need to grab when out of water and really give it some effort to check

I'm really curious about all this ... even more now ....

 

[David 01]

Its definitly a brain pickler! I moved the rudder about when it was out and didn't notice any play however I didn't give it a realy good shake, but the rudder bearings were changed 10 years ago, I have receipts and she hasn't done that much mileage since from my understanding.

 

[Ian_Edwards]

I have a similar problem.
There's no noise on tick-over, as I increase the revs the noise starts, gets louder as the revs increase, then fades away as the engine get closer to max revs. The noise is synchronised with the rpm.
It sounds very much like the clips posted.
Twin rudders.
Engine Yanmar 4JH4E
Python thrust bearing
Conventional shaft.
No play in the cutlass bearing.
Narrow shaft anode
Ambassador rope stripper.
Max Prop, no play in the blades, the boat spends 6 months in the water each year and the prop is greased every winter.
The photo is of the prop just before launch in April 2023. The prop is original from 2007.
It's been like this for 2 seasons, and I've asked various marine engineers, who have looked at the stern gear and no one has manage to identify the problem.
Any thoughts?

 

[David 01]

Its a mystery, I can only think that it is the prop, everything else has been changed by a very good engineer. my prop was new in 2015 with previous owner, when I next get her out im either going to send it off to a specialist or buy a folding and fit that, when, depends on how long I can put up with the noise.

 

[Lightwave395]

My max prop classic has pretty much always sounded a bit like yours for the past 18 years, including before and after a 'rebuild' by Darglow and a change of engine. I guess I've got used to it

 

[David 01]

I think its going to boil down to if I can put up with the noise or not, I've just had a what I think good quote on a new 3 blade flex o fold so it it very tempting if so anybody looking for a max prop?