Singing Prop

[twinboat]

I have a Tohatsu 9.8, 4 stroke.

I pulled the original prop off and put a Solas prop on. Is is a bit smaller pitch but listed to and does fit the engine.

It sings like a lose fan belt at anchorage speed. Idle and fast speed it acts normal.

I swapped it on and off twice to confirm it was on right and it still sings.

Any guess's why ?

[a64pilot]

There is a harmonic vibration set up at that RPM that is sings at.
Look up aeroelasticity for a description

[Hydra]

The trailing edge of the blades might be too thick. On large propellers, a 30° "anti-singing" bevel is often cut on the trailing edge, to create a sharp edge.

Alain

[a64pilot]

Is it "cupped", that is the trailing edge pitched more?
Some props will sing, but a seemingly identical prop, same exact model, won't. Good thing is Solas props are inexpensive.
Something is setting up a harmonic, it can be as simple as a tiny nick on the prop.


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[rwidman]

I have heard that taking a rough file to the trailing edge will eliminate "singing". I've never done it so I can't say for sure that it will work.


You might contact a prop shop and ask them.

[Sailmonkey]

Originally Posted by rwidman

I have heard that taking a rough file to the trailing edge will eliminate "singing". I've never done it so I can't say for sure that it will work.


You might contact a prop shop and ask them.

Backing up through pea gravel will also stop the prop from singing......


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[twinboat]

Pea gravel is hard to find in the Keys but I got a file.

Nothing to lose since Boats.net says, since I put it on, it's used and will not take it back.

They said I should get it checked by a professional. On a 50 buck prop ? Not going to happen.

Thanks for the tips. I'll post results.

[DougR]

Set the prop flat on a table with the leading edge of the blades down against or toward the table. Holding your file vertical, lightly file the trailing edge of each blade so the the trailing edge is no longer rounded, but cut at an angle. This will approximate the 30 degree angle as mentioned by Hydra. Don't take off too much, maybe a millimeter, and do all the blades evenly.

Some years ago Volvo had a singing problem on some of their saildrive props, and I used this procedure to resolve the issue on several props. With a rounded trailing edge the water flow exiting the blade can get into an oscillation, causing the blade to sing. With the bevel, it doesn't happen.

DougR

[twinboat]

She sings no more !!

Got my flap wheel and cordless drill out and did a little sanding on the trailing edge.

Thinking I'm waisting my time, I only did a little bit.

A test run made me a believer when the sound changed along with the RPM, when it made it. A little more sanding and no noise at all.

Thanks to all, for the tip.

[unclemack]

Whew!!!
Lucky I didn't post my brilliant solution - I'd be feeling so dumb now...

[Sailmonkey]

The pea gravel is faster, but I bet your prop looks better than mine!!!


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[markpierce]

The propeller man needed to tune the prop twice (no charge second time) to get rid of the singing.

[twinboat]

No pea gravel in the Keys except Home Depot.

Tried coral bottom with old prop, not good !!!

Besides, they ticket you for running aground here.

[wsmurdoch]

Originally Posted by Hydra

The trailing edge of the blades might be too thick. On large propellers, a 30° "anti-singing" bevel is often cut on the trailing edge, to create a sharp edge.

I have a Nissan/Tohatsu 8hp 2 cycle. I spun the hub in the original propeller and bought a new one two years ago. For two years it would sing everywhere I went. I became quite paranoid thinking that the noise was coming from the gears or bearings in the lower unit.

I read this thread, then Googled "singing propeller", and found this paper http://hydrocompinc.com/wp-content/u...Propellers.pdf . Following its instructions I beveled and blunted the suction side trailing edge using a drum sanding tool on my Dremel.

It worked --- silence. Ten minutes of work got rid of two years of worry.