Hi All,

 

Singing props doesn't appear to have been discussed since 2019 and then only briefly.

Thought I'd see if there were any further thoughts on exactly how to grind the blades to stop it.

 

My prop sing occurs from an engine speed of 900rpm through to 1300rpm (2:1 gearbox)

 

Some people describe a 30deg bevel and some describe a 60deg bevel.

Some grind the suction side edge, some grind the rudder side edge.

 

Would be nice to get it right first time so just seeking the latest thinking 6 years on.

 

Cheers in advance...

17 minutes ago, Telstar said:

Some people describe a 30deg bevel and some describe a 60deg bevel.

Some grind the suction side edge, some grind the rudder side edge.

 

 

I suspect it doesn't really matter what you do, as long as you do *something* that changes the excitement of the resonance(s).

 

 

 

 

I think I'd grind/bevel the whole of the edges of all three blade bats off to sharp.

 

Never needed to though, so I dunno what I'm talking about. (Just so you know!) 

No, not sharp, that is what sets it off! Just blunt it off on the trailing edges, whether at 60 or 30 deg probably doesn’t matter.

8 hours ago, nicknorman said:

No, not sharp, that is what sets it off! Just blunt it off on the trailing edges, whether at 60 or 30 deg probably doesn’t matter.

 

Ok thanks!!

 

I've never had the problem to the extent of needing to actually do something about it, so no direct hands-on experience fixing it. 

We had one set of props that warbled at low speeds.

 

Never really got to the bottom of why as to the naked eye they looked exactly the same as the other spare set that we had. Both sets were bought brand new at the same time and were the same type, make, pitch and size.

 

We just got used to it.

 

Now we just have to put up with nobbly tyre road noise instead 

Thanks guys. I've heard of some instructions provided by Beta.

Does anyone have a copy?

Bee's prop. sings and it is a nuisance, tried sharpening the edges, still the same. The only way to stop it is to wrap half a hundred weight of weed around it, lovely and quiet then.

2 minutes ago, Bee said:

Bee's prop. sings and it is a nuisance, tried sharpening the edges, still the same. The only way to stop it is to wrap half a hundred weight of weed around it, lovely and quiet then.

Well as I said earlier, sharpening the edges is the exact opposite of what needs to be done.

 

We had prop singing when new, dry docked the boat, trailing edge blunted with a grinder, singing ceased. This was done by the builder. About 6 years later it recurred for some reason, just occasionally and not so bad. At the next blacking I took a grinder to it and blunted the trailing edge some more, so far so good.

6 minutes ago, nicknorman said:

Well as I said earlier, sharpening the edges is the exact opposite of what needs to be done.

 

We had prop singing when new, dry docked the boat, trailing edge blunted with a grinder, singing ceased. This was done by the builder. About 6 years later it recurred for some reason, just occasionally and not so bad. At the next blacking I took a grinder to it and blunted the trailing edge some more, so far so good.

Opinions seem to differ on this -- commercial "anti-singing" props like these (used to be Michigan Marine) have ground edges, but it's not clear exactly *how* they're ground...

 

https://nakashima.co.uk/leisure/canal/canal-line-propellers/

 

Looks to me like a thicker blade with the edges ground at an angle and then possibly some rounding of the resulting sharp edge. This is what's fitted to my boat, I'll have a look next time I'm there.

3 minutes ago, IanD said:

Opinions seem to differ on this -- commercial "anti-singing" props like these (used to be Michigan Marine) have ground edges, but it's not clear exactly *how* they're ground...

 

https://nakashima.co.uk/leisure/canal/canal-line-propellers/

 

Looks to me like a thicker blade with the edges ground at an angle and then possibly some rounding of the resulting sharp edge. This is what's fitted to my boat, I'll have a look next time I'm there.

It’s not really an exact science, but I think the main point is to have a blunt trailing edge that results in turbulent (chaotic) flow at the edge, rather than the trailing edge tapering to a sharp edge which results in vortices rather than chaotic flow.
 

Gliders have the same sort of issue, on the underside of most modern glider wings is zig-zag turbulator tape a few inches forward of the trailing edge, its purpose being to force the laminar flow into turbulent flow rather than vortices, resulting in less drag.

Here's a 2016 thread. I've had no problem since then

https://scholargypsy.org.uk/2016/11/05/blacking-and-no-more-singing/
 

 

Interesting article here: https://www.hydrocompinc.com/wp-content/uploads/documents/HC138-SingingPropellers.pdf

8 minutes ago, nicknorman said:

It’s not really an exact science, but I think the main point is to have a blunt trailing edge that results in turbulent (chaotic) flow at the edge, rather than the trailing edge tapering to a sharp edge which results in vortices rather than chaotic flow.
 

Gliders have the same sort of issue, on the underside of most modern glider wings is zig-zag turbulator tape a few inches forward of the trailing edge, its purpose being to force the laminar flow into turbulent flow rather than vortices, resulting in less drag.

 

That's what they seem to be doing, the grinding angle is quite blunt, certainly much more so than a tapered edge would be with a blade that thick.

 

3 minutes ago, nicknorman said:

Interesting article here: https://www.hydrocompinc.com/wp-content/uploads/documents/HC138-SingingPropellers.pdf

 

The drawing in there looks very much like the Nakashima/Michigan propeller.

 

 

Edited September 11, 20251 yr by IanD

When we had our prop replaced after hitting a concrete block it sang at normal cruising speeds. Vetus sent me a sheet which looked, as I recall, much like IanDs. Went up to the top end of the Weaver where the water was nice and clear and took a file to it through the weed hatch. Took a couple of attempts to cure it completely.

Edited September 11, 20251 yr by pearley

I bought the non singing prop which sang very loud leaving the dry dock. I won’t mention the supplier but they told me it was my boat that was the problem not the prop.  Eventually they agreed to supply a replacement that I could fit myself in the water !!! 
Compliments to Midland Chandlers who sorted it and even covered the cost of fitting the replacement.

1 hour ago, PaulD said:

I bought the non singing prop which sang very loud leaving the dry dock. I won’t mention the supplier but they told me it was my boat that was the problem not the prop.  Eventually they agreed to supply a replacement that I could fit myself in the water !!! 
Compliments to Midland Chandlers who sorted it and even covered the cost of fitting the replacement.

Mine (16"x12" 4-blade Michigan Marine/Nakashima, as supplied by Finesse) doesn't sing at any rpm... 🙂 

3 hours ago, IanD said:

 

That's what they seem to be doing, the grinding angle is quite blunt, certainly much more so than a tapered edge would be with a blade that thick.

 

 

The drawing in there looks very much like the Nakashima/Michigan propeller.

 

 

 

Interesting read.

The Nakashima picture shows extensive bevelling to the rudder side of the blades. The hydrodynamic article doesn't state which face of the blade is modified. It does state "trailing edge" but that doesn't define which face.

 

Andy

30 minutes ago, Telstar said:

 

Interesting read.

The Nakashima picture shows extensive bevelling to the rudder side of the blades. The hydrodynamic article doesn't state which face of the blade is modified. It does state "trailing edge" but that doesn't define which face.

 

Andy

It says "typically on the on the suction side", which I assume would be the front (leading) face. But as you say the photo seems to show the rudder side...

 

Maybe it doesn't matter which face is bevelled (or both?) so much as having an obtuse angle not a fine trailing edge?

Edited September 11, 20251 yr by IanD

Yes the front side. Interestingly after I did the work it still sings a bit in reverse at just above tickover, but only if there is no weed or plakky bags or bits of clothing on it. Which is actually quite a useful attribute! Obviously because the trailing edge is the leading edge in reverse!

My Crowther prop has always been quiet, a bit thrashy in reverse as normal.

After it had been chewing bricks on the Ashton canal in low water I had is back to Crowther's ( sadly no longer in business ) for fettling.

They sharpened the leading edges, beat out the burrs and rebalanced it. The trailing edges are radiused, it is silent in forwards.

42 minutes ago, Kingdom Isambard Brunel said:

My Crowther prop has always been quiet, a bit thrashy in reverse as normal.

After it had been chewing bricks on the Ashton canal in low water I had is back to Crowther's ( sadly no longer in business ) for fettling.

They sharpened the leading edges, beat out the burrs and rebalanced it. The trailing edges are radiused, it is silent in forwards.

 

I think this is one of the points - take two seemingly identical props, and you might find that one sings badly and the other doesn't at all.