View Full Version : Noise at low RPM

04-10-2017, 02:32 PM
I hit something submerged over the weekend. Speed was very low but I still damaged the prop enough to require changing. I changed the prop and then noticed there was a "harmonic" sounding ring that developed at low RPM's. It goes away if you increase the RPM's. There is no vibration at any time. Seems so strange as the impact was so minor. Could this be shaft alignment?

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04-10-2017, 02:40 PM
High pitch to the noise? It's likely just prop sing, which I believe is harmless.

04-10-2017, 03:05 PM
From a 2005 MCrew thread:

Hi Steve,

Most of the time the cause of that high pitch wine, or what is generally referred to as "sing", is due to the trailing edges of the prop not having square (or, in other words, sharp 90 degree edges). More specifically, if you place the propeller on a table, with the leading edges of the propeller down on the table, and the tips of the prop up (or, in other words, the trailing edges of the prop are up). The upper most edge should be sharp ----

not rounded off. In other words, the edge formed by the trailing edge of the blade and the top surface of the blade (or the pressure surface), should be very square or 90 degrees ---- not rounded off.

This problem can be corrected with a standard metal file run along the trailing edge of each blade.

(Note, to help clarify this explanation, and that which you want to

accomplish: It is acceptable for the leading edge of each blade on a propeller can be a more sharpened knife-like edge, but the trailing edge of each blade should be more like what you have when you cut a rectangle in half, verses "U"-shaped, which is what you do NOT want, and which is most likely what is causing the sing that you have now.)

If you need further explanation, please feel free to call us. And if you feel uncomfortable trying to correct this issue yourself, you are welcome to send the propeller to us, and we will correct the issue.

Sorry for the inconvenience.

Thank You,

Jim Thelen

Sales Engineer

Acme Marine Group[/I]