Singing Propeller

[haydude]

I read on some threads that to solve a singing propeller issue the trailing edge should be filed. However one post in cruiserforums.com mentions the leading edge instead.

Now I understand that filing the edge might help, however I would like to understand exactly where and by how much.

Could anyone with direct experience (please do not report of other threads as I believe I read all of them), guide me to do it properly?

 

[Deleted member 36384]

You might not want directed to other threads but you do need directed to the answer, which was one click away. To help you: -

Most propeller professionals (and others) are
familiar with the “anti-singing edge” – a chamfering
of the trailing edge, typically on the suction side. The
intent of this shape is to avoid the creation of curving
flow eddies by cleanly separating the flow off of the
blade. The following graphic illustrates the desired
geometry of an anti-singing edge, where points of
flow separation are spaced both in thickness and in
flow-stream position .....

..... sources recommend that the anti-singing
edge be applied from the 40% radius (0.4R) fully to
the tip, or even slightly beyond [Carlton, 1993]. It
has also been noted that erosion of the blade edge is a
risk if the new edge were made too thin.

You are looking for an 18 degree taper.

The source of the information http://www.hydrocompinc.com/knowledge/whitepapers/HC138-SingingPropellers.pdf
http://www.hydrocompinc.com/knowledge/techexchange/tex0303.htm

 

[haydude]

You are looking for an 18 degree taper.

I read that but still it is not clear, do I have to do that over the whole edge of each blade? Or just the tip? To clarify, I understand that the TRAILING edge is the aft, the edge facing back?

What is the 40% radius?

 

[actionoptics]

singing prop

I had an awfully loud and annoying singing at all speeds bewtween 4 and 6 knots. Just the range of normal speeds one would want to use.
I spoke to a naval architect who explained the text book way to cure the problem is to measure the outside of one blade from where it joins the boss to its tip. Divide this by 13 and file a small nick at 90* to the blade at all of the odd numbered divisions.
He then said that the quicker and just as effective way, is to measure the thickness of the blade, in my case it was 3mm, divide it by 3 so that was easy, and file the leading edge of all three blades by a third at an angle of 45* so the file went 1mm down the front and 1mm across the top.
He also said you don't actually have to be very accurate.
I used the quick method on my LM 30 with Bukh 24hp and three bladed prop and the singing was completely eliminated. Not a single note at any speed.

 

[vyv_cox]

Interesting variety of solutions!

My experience with this phenomenon began with Hobie 16 catamarans. Their rudders howl remarkably due to the same hydro-dynamic phenomenon. The cure is to file the sharp trailing edge square, to produce a flat about 1 - 2 mm wide. I did this several times with new boats during our racing career.

I then experienced the prop ringing when we began our change to cruising boats, and solved it in exactly the same way. I filed a narrow flat, less than 1 mm wide, down the trailing edge of the two-blade fixed props on two boats. This completely silenced the ringing.

To clarify for the OP, the trailing edge is the aft, sharper one. I believe that this is excited by the shedding velocity of the water flow. I filed the whole length, tip to hub, probably overkill but the amount removed is tiny.

 

[haydude]

Since english is not my first language I am not 100% sure about what part of the propeller we are talking about. To this point I had understood that the "edge" was the outermost end. If we fit a propeller in a circle with the centre hub in the centre of the circle, I understood the edge was the circumference. The latest poster mentioned the hub, so now I am beginning to understand that the edge we are talking about is the one running on the "radius" of the blade.

I will try to describe a propeller with simple terms, because understanding where to file it is crucial. The "hub" is the centre where the propeller is fitted to the shaft, each "blade" is attached to the "hub". Looking at the blades from behind the boat each have three edges.
1) the edge in correspondance with the circumference of the circle covered by the rotation, we will call it "outer edge",
2) the "forward edge" corresponding to the radius facing the waterflow when the boat goes forward (is this what you mean by leading edge?)
3) and the "rear edge" corresponding to the radius facing behind (is this what you mean by trailing edge?

Each edge then has a side, the forward facing side and the backward facing side (this is actually what I initially understood as being leading and trailing edges ....)

Please could you clarify which edge, side should I file?
I noted also somone else mentioned the "leading" edge suggested by a naval architect, which contraddicts the indications about the trailing edge and makes the whole explanation even more confusing.

 

[penfold]

The diagram on the right here is helpful; the lefthand side is aft, the righthand side is forward.

 

[vyv_cox]

Your "3) the "rear edge" corresponding to the radius facing behind (is this what you mean by trailing edge?" As I said in my post, this is the aft one, usually the sharper one.

"Each edge then has a side, the forward facing side and the backward facing side (this is actually what I initially understood as being leading and trailing edges ....)"
I would substitute 'face' for your 'side'.

I haven't come across the leading edge solution before, so cannot comment. But yes, your forward edge = leading edge.

Your 'outer edge' would normally be the tip, although this implies a point, rather than a line.

 

[haydude]

Thank you for your clarifications.

So what is the "suction side" (see quoted text in first reply)? Is it the forward or aft face?

Also the text suggest to file from 0.4R. Assuming the radius is 10cm. do I start the filing 4cm. above the hub and continue up to the tip (outer edge)?

 

[vyv_cox]

Thank you for your clarifications.

So what is the "suction side" (see quoted text in first reply)? Is it the forward or aft face?

Also the text suggest to file from 0.4R. Assuming the radius is 10cm. do I start the filing 4cm. above the hub and continue up to the tip (outer edge)?

Suction side would be the forward face. That quote is talking about a chamfer of 18 degrees but I have only used 90 degrees.

For the second part I read it as you do.

You don't say what your first language is but I wish I wrote a second as well as you do!

 

[srm]

Many thanks to all of you for this thread. Have been wondering about the painful screaching between 1200 and 1800 RPM since buying Escapade in 2009.
Dried out on the slip yesterday and filed a slight chamfer, about 1 to 1.5 mm wide and around 45 degrees on the trailing edge of each blade from about 0.4R to tip (3 bladed prop). Not much metal removed and not enough to give a feather edge.
Motoring back to the berth the screaching is down to much more modest levels - still some harmonics there but much quieter and pleasanter so will see how we get on this season.

 

[actionoptics]

singing propellor - trailing or leading edge

My humble apologies because I got it wrong.
I have just spoken with my friendly naval architect
and he confirmed that it is the trailing edge that should
be filed by one third of the blade's thickness at an
angle of 45 degrees.
I'm very sorry for causing the confusion but I can confirm
that filing the trailing edge worked on my prop.

 

[spencerd]

Singing prop

Having a singing prop myself on a Bavaria 44, this thread is a god-send. I also have a hobbie 16 and having read earlier comments, the noise is nearly identical in pitch from both cat rudder and cruiser propeller. Filing the 'trailing edge' on the prop I hope will work as it worked on the rudders of the Hobbie Cat.