Singing prop? Or something else?

[richardf]

Hi Folks.

 

Last year we had a refurbed Perkins D3 with a 2:1 PRM (also refurbished) fitted. At the same time the prop shaft was changed and the packing renewed. We only picked it up at the end of last season and it had about 12 hours of running back to base - and then we took her out again this weekend. On Friday we had this loud harmonic sound that seemed to start when the engine was put in gear to pull away out of a lock; it did this twice. It didn't seem to go when additional revs were put on - what seemed to shift it was a sharp rev in reverse. I checked the weedhatch and there was only some light weed around the shaft. I could turn the prop in neutral by hand through the weedhatch.

 

I did notice on our return that the noise did seem to build up slowly - but a quick rev in reverse seemed to clear it.

 

Some possibly useful (most likely useless!) additional info

 

The prop was not changed at the time the engine was changed, to my knowledge, it has not been 'clonked' against anything hard - but it may not be the ultimate size for the boat now.

The stern tube does not leak a drop in forward, but I note does drip in reverse

I'm not sure if the shaft is getting warm as there does seem to be some grey grease on the shaft between the stuffing box and the centrafex coupling

The engine is on solid mounts.

There is a 'clonk' when engaging gears - I have had this before on a PRM, but its not a comfortable sound!

 

It does seem like a prop singing noise - but why would it clear itself when reversed, unless it is a slow build up of crap on the blades?

 

Any ideas very welcome

Thanks

 

[MtB]

Does the note of the singing vary up and down with engine speed or is it a non-changing monotone?

 

MtB

[richardf]

Hi Mike

 

It does vary with engine speed - but you can't rev through it so that it disappears

[RLWP]

Have you got a flexible driveshaft between the gearbox and propeller shaft?

 

Richard

[MtB]

Hi Mike

 

It does vary with engine speed - but you can't rev through it so that it disappears

 

I'm not expert with this, just commenting to get discussion started.

 

I'm very much inclined to think this is a gearbox problem them. A singing prop is the result of a resonance. Resonance is by definition a fixed frequency.

 

Which PRM do you have? A D260?

 

MtB

[RLWP]

 

I'm not expert with this, just commenting to get discussion started.

 

I'm very much inclined to think this is a gearbox problem them. A singing prop is the result of a resonance. Resonance is by definition a fixed frequency.

 

Which PRM do you have? A D260?

 

MtB

 

Or the thrust bearing on the Aqua/Python drive, if fitted

 

Richard

[MtB]

Another thought. You say the PRM is newly refurbished as well as the engine.

 

It's obvious to add oil to the newly built engine. Equally easy to forget to add it to the newly rebuilt gearbox.

 

MtB

[richardf]

There is a Centraflex coupling fitted - but both shafts are very short. Its tight to the stern of the boat

 

Its a PRM 260

 

Still can't fathom why reverse would clear it - but I don't know anything about PRM boxes!

[cereal tiller]

There is a Centraflex coupling fitted - but both shafts are very short. Its tight to the stern of the boat

 

Its a PRM 260

 

Still can't fathom why reverse would clear it - but I don't know anything about PRM boxes!

Could you be picking up "The wrong sort of Leaves"?

 

 

CT

[RLWP]

There is a Centraflex coupling fitted - but both shafts are very short. Its tight to the stern of the boat

 

Its a PRM 260

 

Still can't fathom why reverse would clear it - but I don't know anything about PRM boxes!

 

 

Because it's probably a failing ball bearing. The thrust is in the opposite direction in reverse, so the balls run on the other side of the race. As that side is not used as much, it's probably OK

 

Richard

 

MORE: What does 'both shafts' mean?

Edited April 22, 2014 by RLWP

[MtB]

There is a Centraflex coupling fitted - but both shafts are very short. Its tight to the stern of the boat

 

Its a PRM 260

 

Still can't fathom why reverse would clear it - but I don't know anything about PRM boxes!

 

On reflection I don't think a PRM D260 would work with no oil in it as it's a hydraulic transmission. The oil is used under pressure to change the gear so I doubt you'd get it into gear in the first place with no oil.

 

This propshaft arrangement is new to the boat I think. Is this D3 replacing the Kelvin J3 you removed?

 

MtB

[richardf]

RLWP - I meant the shaft coming out of the gearbox and into the coupling - and then the propshaft running through the stern tube

I can kind of see why there would be more wear in ahead than astern - in which case it would not do it in reverse. But a 'prop clearing squirt of reverse' seems to clear it?

 

MTB - Yes we gave up on the Kelvin P4

Edited April 22, 2014 by richardf

[RLWP]

RLWP - I meant the shaft coming out of the gearbox and into the coupling - and then the propshaft running through the stern tube

I can kind of see why there would be more wear in ahead than astern - in which case it would not do it. But a 'prop clearing squirt of reverse' seems to clear it?

 

MTB - Yes we gave up on the Kelvin P4

 

Redistributing the lubricant in the bearing?

 

Richard

[MtB]

RLWP - I meant the shaft coming out of the gearbox and into the coupling - and then the propshaft running through the stern tube

I can kind of see why there would be more wear in ahead than astern - in which case it would not do it. But a 'prop clearing squirt of reverse' seems to clear it?

 

MTB - Yes we gave up on the Kelvin P4

 

 

Oh yes, a P4. I have the right person and boat though!

 

My point is that I'm asking if this is a whole new installation? Or is it the old prop shaft, thrust bearing etc that worked fine with no singing when the P4 was in there?

 

MtB

[RLWP]

 

 

Oh yes, a P4. I have the right person and boat though!

 

My point is that I'm asking if this is a whole new installation? Or is it the old prop shaft, thrust bearing etc that worked fine with no singing when the P4 was in there?

 

MtB

 

No thrust bearing. It's a centaflex between the gearbox and propshaft, so the gearbox carries the thrust

 

Richard

[richardf]

It's a brand new propshaft running through the original (now repacked) stern tube.

 

It certainly didn't do it the first time we took her out.

 

Richard - I'm in uncharted territory here - could this be a problem of misalignment? The bearings you referred to taking the brunt of it?

 

That clonk going into gear - is that a common PRM thing?

[MtB]

It's a brand new propshaft running through the original (now repacked) stern tube.

 

It certainly didn't do it the first time we took her out.

 

Richard - I'm in uncharted territory here - could this be a problem of misalignment? The bearings you referred to taking the brunt of it?

 

That clonk going into gear - is that a common PRM thing?

 

My PRM D160 (nearly the same) used to 'clonk' if the tickover was too fast.

 

MtB

[RLWP]

The clonk is relatively common

 

The propshaft is relatively fixed, it can't move up and down or side to side. It can move backwards and forwards though. When you go into forwards, the propshaft tries to move forwards (and vice versa). Somthing has to stop it and take the thrust to push the boat forwards. In your installation, that will be the rear bearing in the gearbox. In our boat it is the thrust bearing in the Aquadrive

 

The Centaflex is there to allow the engine to move about a bit on it's flexible mounts, usually not very much. It should allow some misalignment as well. If things are drastically out of line, it could be loading the gearbox bearing undesirably, but I think you would notice it more because of what it will do to the propshaft bearing - like getting hot

 

Richard

 

MORE: What is the history of the gearbox?

Edited April 22, 2014 by RLWP

[richardf]

Thanks Richard

 

To get to the bearings that may be faulty - does that normally necessitate gearbox removal - or is it something at the back of the box that may be accessible in situ?

[RLWP]

Box off I'm afraid. The output shaft needs to be removed and dismantled to get to the rear bearing and seal

 

Before you do though, there is some diagnosis you can do with a listening stick

 

Richard

Edited April 22, 2014 by RLWP

[bizzard]

A singing prop, which pitch is it,'' bass, tenor, baritone, contralto, alto or a couple of sounds mingling, descant?. If the back of the propeller boss is too close to the stern post collar it could rub on it when in forward gear and so make the noise and pull away from it when in reverse and be silent.

[BruceinSanity]

A singing prop, which pitch is it,'' bass, tenor, baritone, contralto, alto or a couple of sounds mingling, descant?. If the back of the propeller boss is too close to the stern post collar it could rub on it when in forward gear and so make the noise and pull away from it when in reverse and be silent.

If he's accidentally left a member of the CID under there, could be a Singing Detective

[nebulae]

If it is a singing prop.the Vetus Catalogue gave some usefull information of how to cure it .I followed the instructions(involved grinding a little off the edge of each blade) .Worked,problem solved.

[nicknorman]

Having had prop singing on a new boat a few years ago, as has been suggested this definitely doesn't sound like it. Prop singing only occurs over a fairly small rev range, so taking the rpm above or below that range makes it stop. The noise itself doesn't change with rpm even in the noisy band. Contamination (weed, poly) on the prop makes it less bad.

 

Although it probably is a bearing, one thing you could consider is some sort of resonance of the fit of the shaft in the stern tube. It might be worth disconnecting the aft bit of the prop shaft and moving the prop shaft forwards and backwards through the tube to wipe the grease around a bit. That said, it does sound like a bearing but sometimes it is a good idea to try the easiest things first, rather than the most probable things.

[RLWP]

I'd try listening to various parts with a stick first

 

Richard