Propeller Shaft Ringing

[sailorbill]

Between about 1200 and 2000 RPM (engine speed), I sometimes hear what sounds like ringing of the propeller and/or prop shaft of a 1983 Sabre 28 sailboat with a Westerbeke 13 HP diesel. This happens only when in forward gear. (If the boat is tied to a dock, it happens only at 1200 RPM... = 600 RPM prop shaft speed. When under way, it may occur over the engine speed range noted.) When the boat was purchased, there were 2 zincs on the prop shaft. I removed one of them last winter. I also cleaned off many years of antifouling paint which had been on both the prop and the shaft. The first day the boat was back in the water this year, the ringing sound appeared... something new. Putting back a second zinc on the shaft did not stop the sound. I don't suspect the transmission, because the frequency of the sound remains the same over the 800 RPM range where the sound is heard. It sounds something like you'd hear when you run a wet finger around the rim of a glass. The cutlass bearing seems snug enough... no noticeable shaft play.
I'd appreciate any advice. Thanks.

[Marksman]

Hi Bill, my shaft is doing something very similar though I haven't logged the offending rpm octaves. I have been suspecting either my stuffing box or my cutless bearing. as they are the only places where this type of friction oscillation could origianate. My cutless is worn and has some play so I tend to favor the stuffing box as the culprit. My shaft started singing only the last couple of times I was out so it is pretty new, and has never done it before in the 4 years I have owned this boat. Do you have a convensional stuffing box or a dripless? I am going to adjust my packing gland and see what happens. Hope this helps.

[MarkJ]

Being a cheapskate I think all these problems are always cheaply fixed... so they must always be barnicales that have grown on the prop or shaft.
But Bill's on started happening on the first day in the water!!

Could it be that the removal of the many years anti fouling on the prop and the shaft has left some reside that might be causing it? A flake of paint in the cutlass? Or did you grind or buff the prop and maybe its out of symmetry?

[sailorbill]

Hi Fred: I have a conventional shaft seal. It drips only occasionally. A marine mechanic I spoke to said that's fine; they don't need to drip as frequently as most people think. I'll replace the packing, because I'll take the shaft out to inspect it better.

Hi Mark: I suppose that some bit of paint might have gotten into the cutlass bearing, but it couldn't be much, because it's fairly tight to the shaft. I did clean the prop and shaft with a wire wheel, being careful to just clean the antifouling off down to the surface of the metal. I doubt that very much brass was removed, but I'll take the propeller to a prop shop and have the balance checked, just in case.

Another marine mechanic I spoke to said he didn't think that this would be doing any harm; it's just a nuisance, he thinks.

[GeoPowers]

This is prop "singing" and is harmless, although can be annoying to some. This sound typically is a clear harmonic tone much like a humming or ringing wine glass. The lower the number of blades on a prop the less chances of "singing". The next time you have the boat out of the water (or dive on it) take a file to the very edge of just one blade. File just enough to see new metal. This got rid of my prop singing.

[GordMay]

Check out ➥ http://www.cruisersforum.com/forums/...-do-15445.html

And ➥ http://www.hydrocompinc.com/knowledg...Propellers.pdf

And ➥ Marine Boat Propellers and propulsion Terminology

[David M]

Cutlass bearings can do this when they are new or start doing this at any time in their life.

[sailorbill]

Thanks, everyone, for your input. The sound is likely propeller singing, and may have started because I cleaned off the years of accumulated antifouling which had been on the prop. Now I'll have to determine if a little rounding of the edges is in order.

[Marksman]

I had just recently cleaned my prop just before the choir sounded off so this makes sense, except that when I installed this prop a couple years ago it didn't do this and it was clean then too. Hmmmm.....

[sailorbill]

Regarding prop ringing, Gord May offered a solution. He provided a link to an article at hydrocompinc.com which showed how to trim a bit of metal from the prop's trailing edge. This worked like a charm. Thanks, Gord!

[Northeaster]

Hi Sailorbill,
If you have a couple of minutes to spare, could you click on the link below, and see if the noise in my video (page 2) sounds anything like the singing propeller that you were able to correct? I woudl really appreciate it, as I have no 1st hand experience in what is or is not a singing prop sound.

http://www.cruisersforum.com/forums/...d-31524-2.html

[sailorbill]

The frequency of the sound heard in your video varies along with RPM, but the frequency of the sound I was getting remained constant in spite of RPM changes. The only similarity is in the fact that it occurs only when in "Forward". I found a clue in that, with the boat out of the water, tapping the propeller produced the same frequency sound as I had heard while under way in gear (forward only).
In your case, I'd think about the transmission, but I'm not an expert. Just a suggestion.

[billr]

Sailor Bill,
Based on your description, the constant frequency you are hearing is likely related to the distance between the cutless and the stuffing box, meaning that the prop shaft has a resonance. When you had the bottom paint on it, the paint (being a compliant coating) would have dampened the vibration. There would have to be some sort of mechanical excitation (prop edge was sited earlier) that starts the vibration. You may have had that condition for some time, but with the paint on the shaft there was enough dampening that the natural resonance never got going. This problem is similiar to what those of us doing environmental testing with vibration fun into with our test fixtures.
Billr