A25 singing propeller ?

[honza]

I have installed the Beta 25 with TMC40P 2.6:1 gear box, new 1 in. shaft and new Michigan Wheel DJ355 16R11 prop. I would be willing to share a couple of observations about the installation, should anybody be interested.

The motor runs beautifully, but between 600 and 1000 shaft RPM in FWD only I am getting very annoying noise, kind of a whine, of a frequency changing with the RPM. (I tried to attach a recording, but the site would not take MP3.) I thought (and I still do) that the sound is coming from the transmission.

I contacted the local Beta dealer, I bought the new engine/transmission unit from and sent cc to Beta Marine NC. After a few emails Stanley of Beta got back to me with the assertion, that I had a propeller squeal and needed a prop shop to fix it. I did some research on the subject, talked to somebody at Michigan Wheel and came to the conclusion, that Stanley might be right. So I did some light filling on the trailing edge to develop approx. 1mm wide flat with square corners to see, if there was going to be any change to the noise. I took the boat for a sea trial, but the noise remains exactly the same.

Has anybody experienced a similar problem? Any thoughts? Thank you.

[WillieC]

Yes. No. New Michigan Wheel prop a couple years ago and I found it annoying at first but had forgotten about it until you mentioned it. We will be launching in a couple weeks and I will see if it's gone or if I have lost even more hearing.

Sorry to not be much help. I'd be hesitant to do much filing on my shiny new prop considering balance. Sounds like you haven't talked to a prop shop, which I get if you didn't buy the prop from them.

The new blade was much thinner than the original. Maybe that is involved.

[DesertAlbin736]

We get similar noises at that RPM range with our Yanmar & 2.6:1 gear reduction. I think it has to do with a harmonic with the shaft. Above or below that range it goes away. We've put over 600 hours on our engine since we took ownership & haven't had problems with shaft, cutlass bearing, and/or prop yet.

Like a 'singing sword', it's witchcraft & 'strictly taboo'.

https://www.youtube.com/watch?v=6u8wBfDtZkE

[honza]

Well, harmonic with the shaft. Why it was not there before? Because the shaft was metric?
DA: Is your gearbox also TMC40P? I suspect that it is the gears. Do you ever hear them big trucks with crappy cheap gears in the rear axle? Sometimes, I can hear them 2 miles away.

[nebulatech]

I'm lost in the woods on this topic, so don't mind me, but is it possible to put the old prop back on just for testing or did you install a new shaft? I dont know if it even makes sense to do that...

[WillieC]

Clearly needs a louder engine or turn the radio up.

[LopezMike]

As long as it's singing opera or Nelson Eddy and Jennette McDonald you are O.K. but when the rap music starts up, shut it down quick!

[honza]

Nebulatech: With the repowering, I had to go from LH prop to RH one and, as I needed longer shaft, from 25mm shaft with metric cone to 1 in. shaft with SAE cone. But, you are right, I have been thinking about trying a different prop and will be looking for one to borrow, if possible.

[ssrig]

The first thing I thought about was the cutless bearing, new one for a new shaft right?
It's like when you take a wine glass and wet your finger and run it around the top of the glass and it sings....
maybe it will wear in and the singing will quiet down but who knows? I find it odd to have that singing from a prop at that lowish rpm though.

[honza]

Too bad I can not post the recording. It is more like not a very good hydraulic pump on a farm tractor or one on the huge forest cutting machine. Changing frequency with RPM.

[nebulatech]

Send me the mp3 by PM or whatever and I'll post it to my web server.

[honza]

I do not see a way, how to attach something to PM. If you send me a PM with your email address, I'll respond with the MP3.

[nebulatech]

PM sent!

[honza]

Some notes about the installation:
- The engine has to go quite forward because of the shape of the cowling and the location of the old attachment bolts, so, longer shaft is likely needed. Also because the new transmission is much shorter. I made kind of a simple wood frame, to simulate the cowling and to see, what was going on.
- Beta prescribes (confirmed over the phone, by somebody in England) the sequence of items on the foot support (from bottom up): regular nut, spring washer, foot, lock nut. I thought, that the spring washer would rive me nuts, when adjusting the alignment, so I used two thin nuts instead. Thin flat wrench is needed for this.
- There is no use to support the 1 in. shaft in the shaft log ("the split hose method") when roughing in the engine. It bends to much under its own weight. It is better just to eye-ball the alignment and support it by the coupling.
- With the flex coupling comes a bolt with a machined head, which is meant to be used with a feeler gauge against the engine flange. Unfortunately, Beta does not supply a flange on the engine side, but something I would call a butterfly. So, the measurement has to be done against the shaft flange. I filled out kind of a nipple on a bolt head for the purpose. The bolts in the coupling are not interchangeable.
- Otherwise, I did not have any issues. It is just a slow going, figuring out conflicts, hoses etc. Now I understand, why boat shops are not crazy, about taking on the job and prefer getting $900 or (much) higher mark-up (my guess), by just selling you the unit and (hopefully) never hearing from you again.
- The standard harness was long enough, but no excess.
I hope it might help somebody a bit in the future.

[nebulatech]

OK, here are the audio files. They should play in your browser just by clicking on them, but if it proves to be a problem, I can quickly code up a browser-based mp3 player. I just don't have time right now. Let me know if anyone has trouble playing the files:

http://nebulatechnologies.net/albin/honza/rpm.mp3

http://nebulatechnologies.net/albin/honza/test.mp3