Whine in saildrive

[jacktheflyer]

Havve just returned my sailing cat to the water after antifoul. Am experiencing high pitched whine from both sail drives between 1600 and 2000 rpm. Had replaced seals on both sd20 drives due water in oil. Suspect may be props singing? Can anyone offer advice on this?
Scrubby


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[Dulcesuenos]

My sd20s have always been whiney. When I pulled them apart to reseal everything looked great no gear wear bearings feel good. May just be the nature of the beast, w the dog clutches and all

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[Rapanui]

When we re-engined our Athena with 3YM30s and SD20s, there was a distinct whine on both in certain conditions both sailing and driving. It turned out the props had been fitted without the tailcones, which are apparently meant to be fitted but not supplied in the package.
Now, we normally only get a low level gear whine when sailing (they are fixed pitch props so rotate when sailing).
You can also get props singing when the blades are damaged or fouled.

[DougR]

It's difficult to see how replacing seals would cause the onset of singing props, if that in fact is what you are hearing. But, a heavy deposit of antifouling paint on the prop blades might. Most prop singing results from rounded trailing edges of the blades, which causes the water flow exiting the blade to get into an oscillating mode. This causes the prop to also oscillate and create the singing noise.

Modifying the shape of the blade trailing edge with a bevel usually solves the problem.

DougR

[Wanderlust]

I just had a wasted exercise pulling an SD20 apart to investigate just such a noise.

The noise could be heard in the cockpit and saloon, but not audible when poking my head in the engine hatch. I had a weeping oil leak from the front seal. With a bit of hard running it must have leaked a bit faster due to getting hot and it was down about 250ml. I suspected I had killed the saildrive due to a bearing running dry.

So with the boat hauled out I had the Yanmar specialists remove and strip it apart. They found nothing wrong! So back in it goes, and this time I had a closer look at the prop and compare to the other side (if only I had done so before ).

The prop on the noisy side showed a slight evidence of contact wear on the outer edge, hardly a mm deep. Fitted to the saildrive there was plenty of clearance, so it must have only moved forwards under load.

So I took it to a prop specialist at Southport and he declared it looked fine. Nevertheless, I decided to get it rebushed which he did within a couple of hours. He also offset the bush slightly to give even more clearance. The removed bush looked perfect. He did say that the original Volvo bush is softer than what he replaced it with.

So, the boat is now back in the water, with me wiser and poorer and no good explanation of what was really wrong. At least the noise is gone and the weeping seal replaced.