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Old 30-03-2021, 00:08   #46
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Re: Propellor interference noise

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Originally Posted by topmast View Post
Can you eliminate other possible causes? Things like engine alignment, a whumpy shaft ,or bent at the cutlass, cutlass failing ,misaligned from birth, or lacking cooling flow due to hidden growth, damaged blade pitch.thust bearing in tranny not happy.?

Some of these, yes, others... hard to tell.

Right now I think the idea about the blunt deadwood is probably on the right track. I’ll experiment next time I slip the boat with some add-on fairing pieces and see if they improve things.
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Old 30-03-2021, 02:09   #47
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Re: Propellor interference noise

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Originally Posted by topmast View Post
Can you eliminate other possible causes? Things like engine alignment, a whumpy shaft ,or bent at the cutlass, cutlass failing ,misaligned from birth, or lacking cooling flow due to hidden growth, damaged blade pitch.thust bearing in tranny not happy.?
Or, for that matter, a torsional vibration in the shaft, which will manifest itself as a high-pitched whine. On an exposed shaft the inevitable growth would unbalance the shaft just enough to damp it away after about a month, but if, as here, the shaft is mainly inside the boat, you'd just have to put up with it—were that in fact the cause, of course.

But the obvious problems are that the aperture is too small in all directions and is blunt both fore and aft (about which defects you probably can't do anything significant); and the prop is too big and has an even number of blades (about which you probably can do something if your pockets are deep enough).

Or you could, as you seem happy enough to do, just put up with it and embrace it as part of your boat's personality.

Slightly off-topic—Topmast, no offence, but the bearing is properly called a Cutless, not cutlass—it's actually one of those product names (rather a clever one in this case) that has become generic, like "Hoover" meaning any vacuum cleaner, or "Thermos" meaning any vacuum flask. I guess a cutlass was a handy thing to have on a three-masted man-o'-war, but a naval sword could take a bit of explaining on a yacht!
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Old 01-04-2021, 19:33   #48
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Re: Propellor interference noise

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.. I guess a cutlass was a handy thing to have on a three-masted man-o'-war, but a naval sword could take a bit of explaining on a yacht!

Would have been handy to hack the kelp off my prop a few days ago.
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Old 01-04-2021, 21:30   #49
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Re: Propellor interference noise

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Originally Posted by Mike Burch View Post
Slightly off-topic—Topmast, no offence, but the bearing is properly called a Cutless, not cutlass—it's actually one of those product names (rather a clever one in this case) that has become generic, like "Hoover" meaning any vacuum cleaner, or "Thermos" meaning any vacuum flask.
I do like people who are authorities on proper names.

Google ngrams suggests you might, at least temporarily, be on the wrong side of fashion.

See attached: cutless bearing vs cutlass bearing.jpg
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