Singing Prop

[DannyS]

Last year, we moved up to a Beneteau 393 and it seems that we have a singing prop. It is quite loud and takes some of the enjoyment out of gliding along with only the sound of water and wind. I brought this up with a Beneteau forum and since I got some inconclusive answers, I thought I'd root around here to see what comes up. My search through the forums here yields similar results but I thought I'd try again with a new post on the topic. I'm almost 100% certain that the singing prop is the issue but I'll lay out my case. The boat makes a very pronounced hum similar to a wine glass rim when rubbed with a wet finger. It only appears at certain RPM, and it doesn't matter if the boat is under power or sailing with the transmission in neutral (Yanmar says not to sail in reverse). The boat has a three blade fixed prop and I've heard some suggest filing an "anti-singing edge" on the forward edge of the prop blade. This "fix" seems pretty contentious as many people argue that this will make the prop unbalanced and will do more harm than good. More research on the subject shows the edge should be filed to a rather sharp edge 40-45 degrees. Others have said the edge of the prop should be squared off to prevent singing so there is quite a conflict in blade edge geometry.
I'm considering buying a feathering or folding prop because this will surely remedy the situation but I thought before I invest such a heavy amount in a new prop, why not see if I can get a relatively conclusive answer to whether or not the anti-singing edge is worth a shot.
Thoughts?

 

[Dave Groshong]

I have never heard of that before, but check the zinc, it could be loose.

 

[DannyS]

I have never heard of that before, but check the zinc, it could be loose.

Thanks Dave, the zinc is solid.

 

[capta]

I've also never heard of that. My mind would tend more toward a dry bearing in the tranny or engine, but before tearing those apart, check the alignment of the engine and if the shaft is straight. after alignment, check the wear on the cutlass bearing.

 

[DannyS]

The singing prop is definitely a real dilemma. Here's one diagram noting how to file this onto the prop but it seems like a last resort.

 

[Hunter216]

The singing prop is definitely a real dilemma. Here's one diagram noting how to file this onto the prop but it seems like a last resort.

This article speaks to filing the trailing edge and your initial post says forward edge so it would be a good idea to figure out where you will file it

To me it doesn’t make sense that the RPM’s of a prop would generate a high enough frequency - vibration to make the prop itself sound like the wine glass noise. The drive shaft rotation causing something else to vibrate makes more sense.

As a test is there a way you can lock the prop from rotating for a short while or remove the prop or borrow a different prop like a two blade or .....to help pinpoint the source?

 

[DannyS]

This article speaks to filing the trailing edge and your initial post says forward edge so it would be a good idea to figure out where you will file it

You see my dilemma! Props have a leading edge and a trailing edge and each of those edges has two sides so figuring out where to file is pretty critical.

 

[jssailem]

I understand the concept. Would not describe the noise as singing, more like groaning, my boat made noise as I surfed a bit down the face of waves till they moved on beneath the boat. It was speed of movement issue. And it came from the prop/spinning shaft/transmission.

Here is what the old prop looked like.

Not only did it groan, but it provided a lot of prop walk and when under power pulled the stern down a good foot bring the exhaust beneath the water line and depositing a lot of diesel soot/grime on the stern.

Here is the image of my new prop.

Better thrust, no issues with exhaust

The new prop, a Campbell Sailor, does not make the noise. I think it is more efficient in design. It does have a blunt leading edge and a progressive curve to the blade not on the old "michigan wheel". This leads me to believe that the noise I was hearing could be associated with cavitation that happened on the edges of the prop blade and tips as the blade speed increased.

That would suggest your altering the prop shape might change the harmonic sounds from such cavitation.

I would be more inclined to discuss this with a competent prop shop. There is some science in altering the prop blades. Errors may come back to frustrate you as it is easy to create imbalances. These can cause more harm.

 

[Hunter216]

You see my dilemma! Props have a leading edge and a trailing edge and each of those edges has two sides so figuring out where to file is pretty critical.

Mind bending for sure Not kidding hard to visualize!

This might help

Terminologies Archive - Michigan Wheel

www.miwheel.com

This is my guess

I think your photo link above is “thinking”that the chamfering would let the water “slide” off the blade without causing turbulence. Way above my pay grade on this one

 

[DannyS]

Looks like I have a similar prop to the one you replaced. I looked at that Michigan Wheel page and I think we’re on the same page about the portion on the prop to modify. Now, would you do it?

 

[Hunter216]

Looks like I have a similar prop to the one you replaced. I looked at that Michigan Wheel page and I think we’re on the same page about the portion on the prop to modify. Now, would you do it?View attachment 188733

Not sure who you are asking. If it’s @jssailem I would value his opinion. If it’s me @Hunter216 then I would be careful as the power on my “Yacht” is a tiny Honda outboard.

Since you might be asking me I wouldn’t do anything to what appears to be a pretty expensive prop on the “speculation” it might fix your problem.

Take some time to pinpoint the source of the noise and then go from there OR if you are convinced it’s the prop - change it while you are on the hard and cross your fingers you are right

 

[DannyS]

I thought I’d share a video of our delivery of the boat where you can plainly hear the humming throughout the video. It comes and goes in the clip but that has more to do with the direction of the phone. The him is constant then sailing at certain speeds.

 

[jssailem]

That sound is relatively consistent. Pitch and hummers could be the shaft. I would open up the engine compartment and try tot isolate the sound source. I note th at you are sailing. It appears you may have rod rigging. It might also be in the rigging. Sometimes the rigging starts to vibrate and you get that thrumming sound. Check all of the standing rigging and halyards.

 

[DannyS]

Thanks for having a look. I’ve been in the engine compartment while the humming has been going on and it’s definitely happening down there and not up top. The hum is very consistent at certain speeds and RPM while under power.

 

[Claude L.-Auger]

Since you say it does that ''singing' also while under sail, it cannot be engine related. Under sail, as per Yanmar, it's in neutral so it is free wheeling. Proceed by elimination: Start by putting a stethoscope (or a long wooden handle) on the tranny and listen. Then put it on the packing gland, then on the stern tube. Since the singing could come from everything from the tranny to misalignment to cutlass bearing to prop you can at least check what is inside the hull. I'll also add my 2 cents to the suggestion of locking the propeller for a little while when under sail. Put her in reverse. That will lock the prop. You can do it for a certain amount of time (it used to be Yanmar recommended that !). If there is noise without shaft turning, I would see if I could borrow a prop, hire a diver (if boat in water) to have it installed and go try the boat with the engine and also under sail. Good luck.

 

[justsomeguy]

A singing propeller?
I can't help myself...

 

[CarlN]

Do you have a prop shaft ground brush to keep the shaft and propeller connected to the boat's ground? I once had a singing noise that went away the moment I moved the brush off the shaft.

 

[DannyS]

Do you have a prop shaft ground brush to keep the shaft and propeller connected to the boat's ground? I once had a singing noise that went away the moment I moved the brush off the shaft.

CarlN, I don’t think so but not sure. Does that brush ride on the shaft between the transmission coupler and the shaft log?

 

[Ward H]

@DannyS
I get almost the exact same humming at times on my C30 with a 3 blade fixed prop. When under power it occurs around 1200 to 1500 rpm and when over 2 knots of speed. When sailing it occurs around 5 to 6 knots of speed with tranny in neutral. It stops when I lock the tranny.
I checked the drive train with a stethoscope and am sure it is coming from either the cutlas bearing or prop.
I didn't have any humming the first season I had my boat. Before launch for my second season I polished the prop with brass brushes in a drill. Immediately on launch I started getting the hum. The yard mechanic and some others suggested I rounded the prop edges too much when wire brushing and I needed to square them. I tried this with the boat in the water and the hum stopped for a short period and then returned.
Last spring I had the prop refurbished by a prop shop. My marina sent it in so I didn't talk to them directly.
When I got the boat back in the water the hum was still there but the condition that would cause it changed slightly.

I guess I didn't research it enough as I hadn't come across the above link to singing propellors.

This year I'm seriously considering switching to a Campbell Sailor prop as the hum is most annoying and I'd like it gone.

 

[DannyS]

@DannyS
I get almost the exact same humming at times on my C30 with a 3 blade fixed prop. When under power it occurs around 1200 to 1500 rpm and when over 2 knots of speed. When sailing it occurs around 5 to 6 knots of speed with tranny in neutral. It stops when I lock the tranny.
I checked the drive train with a stethoscope and am sure it is coming from either the cutlas bearing or prop.
I didn't have any humming the first season I had my boat. Before launch for my second season I polished the prop with brass brushes in a drill. Immediately on launch I started getting the hum. The yard mechanic and some others suggested I rounded the prop edges too much when wire brushing and I needed to square them. I tried this with the boat in the water and the hum stopped for a short period and then returned.
Last spring I had the prop refurbished by a prop shop. My marina sent it in so I didn't talk to them directly.
When I got the boat back in the water the hum was still there but the condition that would cause it changed slightly.

I guess I didn't research it enough as I hadn't come across the above link to singing propellors.

This year I'm seriously considering switching to a Campbell Sailor prop as the hum is most annoying and I'd like it gone.

I looked into the Campbell Sailor prop and that is a strong alternative to any feathering or folding prop. We don’t race so speed isn’t the issue. Maine Sail’s critique of that prop is enough to push me in that direction and for the price, it seems a no-brainer.