Hey Folks! I have a little engine/prop riddle that I am trying to solve and I thought that I would share it with you. Last April, I splashed my Morgan 321 after having the cutlass bearing and shaft replaced and my prop worked. I had the prop reduced by two inches in pitch. When I ran the boat under power, I would get a ringing noise from about 1600 through 2200 RPM. Noise would go away after that. I thought that the bearing might need to wear a bit and decided to let things ride a bit. After two months or so, the ringing noise was gone... great! Then this last weekend I hopped in the water and scraped off all the barnacles from my prop. It was fouled and I felt the engine (Yanmar 3GM) was more loaded. Boat runs great with the prop all cleaned off... but guess what... the ringning is back! Has anyone had a similar experience? I am puzzled about what part of the mechnanism to suspect. Any ideas would be really appreciated! Thanks, Kevin
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Prop re-pitching
Assuming it is a fixed prop the blades might not all be the same pitch. Just a slight difference can set up a harmonic in any prop that meets the water stream at an angle. Does the ringing happen when the boat is stopped and you have the engine driving the prop at those speeds? Tie up at the dock and see if you can get it then. The water moving past the prop will be downward along the axis of the shaft and not at an angle as when the boat is moving. The baranacles may have made the prop inefficient enough to negate the ringing.
Assuming it is a fixed prop the blades might not all be the same pitch. Just a slight difference can set up a harmonic in any prop that meets the water stream at an angle. Does the ringing happen when the boat is stopped and you have the engine driving the prop at those speeds? Tie up at the dock and see if you can get it then. The water moving past the prop will be downward along the axis of the shaft and not at an angle as when the boat is moving. The baranacles may have made the prop inefficient enough to negate the ringing.
Only you can hear the ringing
hard to analyze without conjecture of the wildest proportions. Most boats (at least ours) have resonant frequency ringings, which could be from lots of things: your ideas, engine alignment, engine mounts, loose stuff in the galley.... ??Send us a tape of the noise?? *! *x
hard to analyze without conjecture of the wildest proportions. Most boats (at least ours) have resonant frequency ringings, which could be from lots of things: your ideas, engine alignment, engine mounts, loose stuff in the galley.... ??Send us a tape of the noise?? *! *x
Prop Noise
We had a ringing on a brand new boat's prop. Hunter's dealer, Tidewater, said the solution was a little discrete filing of the prop's blade. They did and it worked. Perhaps a call to your prop MFGR would be appropriate now to answer the question.
We had a ringing on a brand new boat's prop. Hunter's dealer, Tidewater, said the solution was a little discrete filing of the prop's blade. They did and it worked. Perhaps a call to your prop MFGR would be appropriate now to answer the question.
Using a hammer
Ross, do you mean to use the hammer with the prop in the water or removed? WJ, do you have any insight into how the folks at Tidewater knew what blad edge to file? Kevin
Ross, do you mean to use the hammer with the prop in the water or removed? WJ, do you have any insight into how the folks at Tidewater knew what blad edge to file? Kevin
Singing Prop
I bought a new fixed prop and it made a high pitched sound through some rpms after installation. No vibration just whine. I called the prop shop and he said that on occasion a "singing prop" shows up. He told me to bring it in and they would file the edges (not repitch) and that should take care of it. It works fine now. I wouldn't beat on one with a hammer. Dan H 45
I bought a new fixed prop and it made a high pitched sound through some rpms after installation. No vibration just whine. I called the prop shop and he said that on occasion a "singing prop" shows up. He told me to bring it in and they would file the edges (not repitch) and that should take care of it. It works fine now. I wouldn't beat on one with a hammer. Dan H 45
Prop Noise
Magothy Boy: Don't know, but you could e-mail Joe Fallon who is in charge of repairs at Tidewater, Harve de Grace, MD and ask him. Joe can be reached at 800-960-8433, ext 123. You probably won't get Joe directly, but tell Judy, his assistant, what your question is and your e-mail address, and Joe will get back to you.
Magothy Boy: Don't know, but you could e-mail Joe Fallon who is in charge of repairs at Tidewater, Harve de Grace, MD and ask him. Joe can be reached at 800-960-8433, ext 123. You probably won't get Joe directly, but tell Judy, his assistant, what your question is and your e-mail address, and Joe will get back to you.
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