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Singing propeller


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Around 1200 revs, my propeller 'sings', it stops at 1300 revs. I thought it was a whine from the alternator belt, but changing the tension does not alter the 'singing' and the temperature of the engine also doesn't.

 

I was told that I could have the prop taken off and re-balanced (I think that was the term used), but also that an easier 'fix' could be to file a small notch into one of the blades. As this could be done in the water, it is a more obvious way to start.

 

However, I really don't want to start messing with my nice and shiny new propeller without getting more advice.

 

Anybody tried this? Did it work? How big is a small notch?

 

Thanks folks

 

Kevin

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We had same problem last year with a new prop although at lower revs. Particularly embarrassing when passing moored boats. Vetus sent me a PDF about taking an angle grinder to the back edge of the tips. We went down onto the Weaver so we're in clear water and could see what we were doing and took a file to it. Now it's great.

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3 hours ago, Kendorr said:

Around 1200 revs, my propeller 'sings', it stops at 1300 revs. I thought it was a whine from the alternator belt, but changing the tension does not alter the 'singing' and the temperature of the engine also doesn't.

 

I was told that I could have the prop taken off and re-balanced (I think that was the term used), but also that an easier 'fix' could be to file a small notch into one of the blades. As this could be done in the water, it is a more obvious way to start.

 

However, I really don't want to start messing with my nice and shiny new propeller without getting more advice.

 

Anybody tried this? Did it work? How big is a small notch?

 

Thanks folks

 

Kevin

I see that you are in Hull. Before doing something drastic, try having a word with Woodwards who are in Hull and  very knowledgeable about marine propellers.

 

Link here   http://www.aewoodward.co.uk/

 

Cheers

 

Howard

 

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1 hour ago, howardang said:

I see that you are in Hull. Before doing something drastic, try having a word with Woodwards who are in Hull and  very knowledgeable about marine propellers.

 

Link here   http://www.aewoodward.co.uk/

 

Cheers

 

Howard

 

Thanks Howard, I'll do that before I start on it.

 

Kevin

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We had this on our second share boat.

 

The boatyard where it was moored resolved it by filing the trailing edge of the propellor. However they did say that any singing props cure themselves after a year or two as the blades get nicks in them from hitting underwater obtructions.

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2 hours ago, cuthound said:

We had this on our second share boat.

 

The boatyard where it was moored resolved it by filing the trailing edge of the propellor. However they did say that any singing props cure themselves after a year or two as the blades get nicks in them from hitting underwater obtructions.

In our case, the singing came back after we got stuck on the CRT-provided rocks and stones below Minworth middle lock. This was about 7 years after we’d “fixed” the original problem. Prop received a number of nicks which brought the singing back. So I don’t think you can say that nicks accumulated over time will cure the problem necessarily.

Edited by nicknorman
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On 18/05/2019 at 09:21, nicknorman said:

Yes the standard fix for singing prop is to use an angle grinder to put a 60 deg chamfer on the trailing edge (back edge) of the prop. One needs to avoid any suggestion of a sharp trailing edge.

Exactly which edge is that please? The front or back of the trailing edge? Or both?

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Well, I never got chance to do anything before setting off, but I think I've found the answer.

Today I left Keadby Lock about 7-30, by 4-00 I was passing through Cromwell Lock and decided to head for the pub at North Muskham, the last 2 miles on the non tidal Trent were nice and quiet from the propeller at 12 to 1300 revs-  so the answer is obviously 45 miles and 8 hours at 1600 revs on a flood tide and the singing will stop ?

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14 hours ago, Keeping Up said:

Exactly which edge is that please? The front or back of the trailing edge? Or both?

 

I'd say it doesn't really matter, either will do. The point is to slightly change the balance of the hydrodynamic forces on the blades, so the resonant frequency of each blade no longer gets excited. 

 

 

 

Edited by Mike the Boilerman
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Here is how I solved the problem, this contains some links to other sources and shows exactly where to file (not nick(. It worked a treat.  The only problem is that the rev counter doesn;t work, so its a bit harder to judge our normal cruising speed (which was "just above the whine"),

 

https://nbsg.wordpress.com/2016/11/05/blacking-and-no-more-singing/

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My wife used to work as a flying sister for the Australian flying doctor service, Said the pilots routinely checked the props for stone damage and carefully filed the nicks out.

About once a year I would run a file around both edges of the prop blades to remove the burrs and bruises. The trailing edge in particular could develop some overhangs. I am sure the boat went better and quieter, otherwise there was no justification for spending uncomfortable drinking time down the  weed hatch.

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I suspect it doesn’t matter too much whether pulling side or pushing side. The important thing is to have a discontinuity ie sudden change of angle, rather than a curve or worse a taper to nothing (sharp) blade.

Edited by nicknorman
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36 minutes ago, nicknorman said:

I suspect it doesn’t matter too much whether pulling side or pushing side. The important thing is to have a discontinuity ie sudden change of angle, rather than a curve or worse a taper to nothing (sharp) blade.

 

Me too. I think the point is most props don't sing but those that do, seem to get fixed by tiny changes e.g. a nick in the leading edge, or a few thou' filed off part of the leading or trailing edge. 

 

The downside is there are (usually) three bats and probably only one is doing the singing, but you need to make a change to all three bats as you dunno which bat is the culprit. So you risk introducing a song to each of the other two.

 

Edited by Mike the Boilerman
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Some of the boatmen thought they were prop experts and used to use Braunston bottom lock cill to have a go at the blade to give it more “lift” and make the boat a bit faster. It’s a fine art to get the level right so the prop is visible and only with an empty.

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