Awful noise.

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Paulka

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I was crewing for the first time a friends Hallberg Rassy 40, for a 4 days cruise in the Med.
Unfortunately, there was very weak winds, and most of the cruise went on engine.
The boat is now two years old, the engine has clocked 2000 hours,
The boat – probably not the engine itself – develops an unsustainable noise.
Staying in the aftcabin was (still is) like staying just in front of a B747.with running engines!
According to the owner, this noise plagued her since new.

The engine is a 40HP 4 cylinders Yanmar (no turbo), connected directly to the shaft.
The gland is a Volvo one, the propeller is a Maxprop.
Thus nothing exotic and everything well engineered as can be expected from Hallberg Rassy.
When motoring, up to 1500 RPM, everything goes nicely, then, when accelerating, a high frequency noise develops to get unsustainable at around 2200RPM and more.
As said, the noise is quite comparable to the noise of a gas turbine.
Trying to localise the source, we found out that it does not originate in the engine room, which is very well isolated.

My suspicion is the bearing being either of the wrong dimension, or material.

I would thankfully read of any suggestion, experience, opinion about any sort of remedy to this very, very annoying noise, and how to get rid of it.

Thanks in advance to the experts.

Paul
 
have you considered prop cavitation ? High frequency "singing" is a symptom thereof.


IS the prop smooth or dinged ?
 
It sounds as though it might be coming from the cutlass bearing but 'why' is another matter. Given the long-standing nature of the problem it doesn't sound like marine life in there but could be misalignment. I would be inclined to get her out of the water and draw the shaft, and check alignment very carefully....there might be some signs of wear given the high level of sound over such a long time.

Since this has been happening since new, it would be worth asking the same question of the boatbuilder and commissioning engineers.
 
pitch easy.
find out max rated rpm for the engine
run @ full throttle under way
does the engine attain the max rated
if any difference adjust the prop pitch to suit ( see MaxProp manual )
a slight over pitch is best reducing the max rpm by say 200 rpm, this will help in motor sailing
 
Most noise in marine transmissions comes from the shaft, as thrust is applied to the end of the shaft along with torque the unsupported section will be inclined to bend and twist. Rubber cutless and stern tube bearings and the engine moving on its mounts allow this to happen.

If a shaft is supported along its length in bearings that hold the shaft true the noise levels are reduced considerably.

Without changing the set up drastically, he could look at accurate alignmnet and dare I say it trying a composite bearing instead of rubber as these run close tolerances and are rigid. The shaft/bearing carrier alignment can be checked easily using a clearance fit bearing. If everything is true with the shaft supported the bearing can be slid into the carrier and will turn easily. The bearing can now be epoxied in place. Now you can go to the engine and get the feeler guage out.

However with any soft mounted drive where thrust is taken on the engine mounts the system goes out of alignment when thrust is applied as the engine moves! so this system will always have noise and vibration associated with this movement.
 
Are the trailing edges of the prop blades sharp? I've had similar symptoms which were relieved by filing the trailing edges until they were about 1mm thick. Made no discernable difference to the performance, but a lot to the noise.
 
I think you may find it is a characteristic of the design of the propeller. The blades are flat rather than shaped and they can be noisy. It is something that can occur in all designs of feathering propellers, not just the Max Prop. The noise can be exaggerated in the aft cabin which acts like a sounding box. A slight change in pitch to alter the angle of attack of the blades to the water may change the sound. The only way to eliminate the propeller as a source is to try a fixed pitch one. Worth checking the cutless bearing for marine growth inside if the boat stays idle for long periods. However, this usually results in a high wear rate rather than noise.
 
I agree with posts that talk of prop ringing. If it's this, the problem can be solved by modifying the leading edge of the prop blades. It is surprising how a little amount removed with a fine file can "de-tune" the prop and stop it. What is actually happening is that the prop is "in tune" with a harmonic of the vibration caused by rotation at a certain RPM and then rings like a bell. If you are not confident to file the leading edge yourself take the prop to a "prop shop" but it's an easy job...

The other thing is that the boat itself can be attuned to the vibration set up. On my own boat, which is a cat, the tension of the backstays is critical. At a certain tension, the whole boat sounds like Jimi Hendrix playing "Watchtower" out of key! A couple of turns on the backstays and it is tuned out.... Have fun!
 
Ah, that's good. I thought you had a new one that I hadn't heard of!

One of the best examples of this phenomenon that I have come across was the rudders on Hobie 16s. Out of the box the rudders would emit a loud wailing noise at wind speeds over about force 4. This could get really annoying over a long race or a regatta. Running down the trailing edge with a file, making a flat line about 1 mm wide, would completely silence them.
 
Not sure this would work on a Max Prop as the blades are not shaped and are much thicker than on a conventional prop. My feathering prop also makes a noise at certain revs, but it is not under an aft cabin and is drowned out by lots of other noises. Volumious aft cabins tend to amplify any stern gear noises.
 
Almost without doubt this is a singing prop - you will get lots of info under that title if you do a search here.

The prop has a defect - very small - in its trailing edges that set up resonannce when it hits a certain speed. Pushing on up through the revs can eliminate it: if so, this is confirmation that it is not a bearing or other item failing.

Your solution is to return the prop to a prop specialist and it can be removed by fine tuning. But beware - such attention can move the range of vibrations to another sector, and you may be no better off!

Rest assured, apart from the damage to your ears, you are doing no other damage by running on! That you have had this since launching is further confirmation of the diagnosis.

Finally, my prop suffers from this - fortunately only at low revs so I can move on up and eliminate the noise. I sympathise......

PWG
 
Thanks to all contributors.
I shall submit your suggestions to the owner, he should decide what to do.
He will now be able to argue with either Max-prop, or HR, or both.
And ... I may have a better sleep in the aft cabin.

Paul
 
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