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Old 28-09-2016, 03:15   #16
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Re: 3YM20 muted screeching noise under way

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Originally Posted by danstanford View Post
Have now had her out a couple of times and we love almost everything about her! The noise crops up at just over 1000 rpm and seems to almost entirely go away by 2000 rpm. Last night I was cruising into the marina at too high a speed so I dropped down to about 1500 rpm and the noise sounded horrendous like some bearing was about to seize from running dry. I threw her into neutral and the noise went away so it is definitely somewhere in the propulsion system. The PO's said it was always there and they just put it down to some kind of resonance at that rpm range and didn't run her there.
I did notice the water pump">raw water pump drive belt seemed loose but we have a good flow of water at idle and when running so that seems unlikely.
I am going to try the listening method with a length of hardwood and a screw driver but am wondering if someone has an idea how to really test the prop/prop shaft system other than listening?
Dan
Sounds exactly like my singing props. (3Ym30+SD20) started after the last antifoul. Will go away as the props get dirty.

Scrubby
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Old 28-09-2016, 12:30   #17
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Re: 3YM20 muted screeching noise under way

Recorded the sound yesterday when I was out. The rev range is narrower than I had previously thought starting about 1200 and stopping about 1800. When revved in neutral or through the same rev ranges tied to the dock the sound does not occur. When on the water moving it happens at the same rev count every time and doing things like swerving do not make it change.

Posted it on youtube:

https://youtu.be/hEd0IH6grw4

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Old 28-09-2016, 14:06   #18
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3YM20 muted screeching noise under way

Sure sounds like a prop to me, that whir sound is what makes me think that.
I've never had one sing myself although I have heard that filing the trailing edge of the prop at a slight angle will stop it, by that I mean like you were sharpening one side

Call a prop shop though before you go filing on your prop


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Old 28-09-2016, 16:40   #19
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Re: 3YM20 muted screeching noise under way

You have a Singing Prop, as mentioned by a64pilot remove the Arris from the trailing edge of the Prop. It should only take a few File strokes as it only requires the profile to be altered slightly. I have seen the job done with vessel in the water on both Boat & Ship Props.
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Old 29-09-2016, 01:20   #20
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Re: 3YM20 muted screeching noise under way

I may have missed what engine/drive combination you have, but if it is a Yanmar with SD20 saildrive it could easily be singing from a wrong installation. We had this on both of our replaced engines, turned out to be that the fixed pitch props were not installed with a tail cone rather than a nut.
Talking to prop people at a boat show last week, this occurred because the saildrives are shipped with a nut for a folding prop as standard. If you fit fixed props you need tailcones, its in the installation instructions but pros never read them.
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Old 29-09-2016, 02:49   #21
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Re: 3YM20 muted screeching noise under way

Beneteau 323 2007. Yanmar 3YM20 with fixed prop shaft. The zinc is kind of a tapered cone installed after the prop.
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Old 25-10-2016, 15:56   #22
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Re: 3YM20 muted screeching noise under way

I say stern gland/stern tube bearing. Bet the noise goes away after you motor through a patch of weeds.



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