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"Singing Prop"

V

Victor Copelan

Member
Yea, I know this is a strange one....

Two weeks ago I finished the second installation of a new engine in less than a year. This one seems to be a keeper but that is another, long story.

Either the transmission or the prop "sings" for lack of a better description - the sound it makes if very musical. At about 1000rpms a sound like the harmonic you get when you wet your finger and rub it on the rim of a wine glass. At 1100 rpms it deminishes to the point it is tollerable but is still there all the way thru the rpm range - at 1000 to 1100 it is loud.

The transmisssion is hydrolic made by twin disc, shaft is 1 1/4", distance from cutlass bearing to prop is about 2 1/2", prop is a new 17x12 Michigan Wheel (I had it balnced & mated to the shaft). Beta Marine, the engine manufacture says it is the prop making the noise. I tend to agree with him but have been snake bit once too often.

Any thoughts?

Thanks,

Vic C



 
Vic
Could the 17" wheel be too close to the upper and lower parts of the aperature? The biggest prop I've heard of on the Morgans is a 16". Maybe the narrow space as the blades (Three I assume)on the 17" wheel pass the hull causes the harmonic sounds.
 
Is it really annoying? A lot of the science between engine, prop, and boat is really black magic. What happens at cruising rpm? a 3 blade 17 x 12 sounds like 7 knts. at 1800 rpm, but I'm just guessing. The noise might disappear after a break-in period. And then again Jim might be right. The aperture might be a bit tight for 17 inches. It might be borderline, and that might be the cause of the hum. All in all if the combo of engine, transmission and prop and working well, sing on. It's much better than the grumble, grumble that you get on some boats.
Larry
 
Vic. My guess is that it is the cutlass bearing. If it is a loud noise, then you should be able to find it. If possible, moor the boat along a pier start the engine, engage the transmission and go below and feel, look and listen to the different parts of the system and try to isolate the vibration. Try the same while underway, with help of coarse. I don't think a prop, turning at 600 RPM (I assume you have a 2:1 ratio) would produce a high pitch sound, like a finger on a wine glass. Good luck.

Jay
 
The aperture is plenty big for the 17". I measured before I bought the prop. We have almost 4" of clearance. One more bit of info. It doesn't do it in reverse. The harmonic is OK at cruising RPM but after a few hours it starts to grate on your nerves. The pitch is rather high - sort of like finger nails on a blackboard, tolerable but marginal. I really want to make sure it is not a transmission thing. I have had so much bad luck with this project I am truely gun shy and every anomily scares me.

If it is the prop then changeing it or shorting the shaft will probably stop the harmonic. In order to accomindate the engine in the box I had to move the coupling about 1 1/2" back and there fore the prop is further back in the apeture. At this point I am just scratching my head and picking yours. If any of you have any additonal thoughts please share them.

Speed is more like 6.8 at 2200 and 6.1 at 1800.

Vic
 
Vic,
Jay might be right about the bearing. I had a volvo that had a bad wheel bearing and it made the noise you describe. It made the sound that heavy duty wide tread snow tires make on a dry road.
By the way, what engine and trans. did you put in, and are we all correct in assuming that you installed a 3 blade prop?
Larry
 
Try feeling around with your fingers. Set the RPM to max noise and see if you can find an area where the vibrations are the strongest. This might help you localized the source.

Jose
SV Siboney
 
Vic
What if you disconnected the shaft coupling and ran the engine at 1000 rpm in forward? If no noise then you can assume it's in the shaft & prop, No?

Jim
 
Vic,

two suggestions

1. a long, (enough), metal rod held against various locations and held against your ear, (fold lob back into ear), may help locate source of noise.

2. a piece of hose will accomplish the same and has the effect of locating your ear at the open end of the hose.

The noise you describe is multi Khz. Hard to believe it is from a prop or shaft rotating at 500 rpm and dampened with water. Same with engine. My guess, and I hate to say it, is that the noise is a gear whine from the transmission.

The reason that it is loud at 1000 rpm and diminishes with speed is probably due to a resonance at the point of origen.

Good Luck, sounds like a serious problem, I wouldn't just live with it until I knew what it really was.

If the trainy is your old one, perhaps there is a clearance problem with the spline coupling at the engine that loads or loaded the front bearing and displaced the input gear rearward during installation. Also, the prop thrusts against the tranny in opposite directions in fwd and rvs.

Not trying to be a pessamist, just trying to help.

Plz advise progress and resolution.

Bill Buebel
 
Years ago my dad installed a new Perkins 4-99 in his boat. The Paragon reduction/reverse gear sang like this--and we determined it was going to give out. Among other things, we checked the gear's oil temperature periodically and it was much too high. (Don't remember the numbers.) I hope that is not the problem, but if it is, the gear can be replaced or repaired without pulling the engine. That much I know from replacing my Hurth transmission two years ago. Good luck.
 
Thanks for all the input. I have down with a cold most of the week but plan on looking into it more closely this weekend using some of the techniques you guys suggested. One thing I am surely gonna try is to disconnect the transmission and run the engine/trans at 1000rpm. However, I'm not sure this will give an absolute answer becasue the transmission is not under load.

The transmissions is brand new and came with the engine, uses ATF, built by Twin Disc, 2:1 reduction. I hope it is not a transmission problem. Could over or under filling the transmission cause funky harmonics?



Vic
 
Vic: I agree with the group who think it's the trany. I don't know your engine or the coupling on the shaft but you could probably rig up some type of pony brake on the coupling or the shaft with the coupling removed to induce a load. The bearings in the trany are probably better rated for thrust loads than axial but should take some axial. Be very careful if you do this and check with Twin Disc as to location of loading shive on the shaft. You have had too much trouble with this project. Good Luck

Dick
 
I finally answered this one. It is the prop not the transmission. The prop sings under sail as well as power. Now the only question left is why?

I suspect I will be changeing a prop some time in the future.

Vic
 
Vic,

I hope you are right but! The but is that in forward or neutral there are still rotating components in the transmission. I understand that our transmissions will lock and prevent prop rotation in reverse.

I just can't envision the physics of a prop singing other than, perhaps, the cutlass bearing, but I've never heard of that.

Bill Buebel
 
It occurs when the transmission is in neutral. My transmission (twindisc) recommends neutral, not forward or reverse for sailing...and I too hope I am right.

I have used rubber tubing as a stethicope and the harmonic seems to come from the prop shaft not the transmission. The transmission is isolated from the shaft by a flex coupling.

But, I too agree that there is still a chance it is the transmission but less of one. Beta marine swares it is the prop. Claims he has had the experience once before and changing the prop fixed the problem.

The physics of the situation have driven me nuts also. The only thing I can visualize is the prop is acting like a "bell." There is just enough back pressure from the apature that it "taps" the blades as they pass thru and therefore the "ringing" sound. Who knows?

I'll let you know when I change out the prop but that will be a while.


Vic C.

Vic C.
 
Vic,

I have a thought!

The flex coupling has a spring rate. Every thing does but a flex couple is low compared to a direct couple which is, obviously, very stiff.

The propeller/shaft system probably has a breakaway friction that is different than the running friction.

I believe that it is quite possible that this could cause the noise and vibration that you hear. Like the noise you sometimes hear when you tighten or loosen a nut.

Perhaps a slight adjustment to the stuffing box, some lubricant, or both will correct the problem or at least change the symptom so that you know that you have a handle on it.

I still can't envision the prop as the problem. It has a resonant frequency but that frequency does't change with rpm and is furthermore heavily damped by the water. Think about ringing a gong under water, it would just 'thud'.

Remember, the prop is only turning about 8 turns/sec at 1000 rpm and you are hearing about 1000 events/sec.

Hope you, (we), figure this out soon.

Bill
 
Bill,

I will try lubing the flex coupling but I do not believe it is making the sound. The sound has a true bell like quality similar to the ringing you might here if you tapped the prop out of the water with a mallet. I don't think it could be stuffing box because it was not altered in any way with the change in engine. Only the flex coupling, engine & transmission were changed out.

Maybe I should take the flex coupling out of the system and see what happens. When time allows I'll try that also.

If the flex coupling is not it then I will change out the prop in the spring and see what happens.

I agree with diagnosis, by the way, but I was grasping at straws.

Thanks,

Vic
 
Vic,

What flex coupling do you have?

I've been contemplating one for my boat but havn't done it yet.

I think testing with direct drive is a good idea and test. A pain but a good test.

Good idea and time to check shaft alignment in the water also.

Also pretty much isolates the prop as the problem.

Bill
 
Jose,

Not now, but that is a long sad story...

It started with a Yanmar engine. Well, you can't remove the prop without droping the rudder.

I changed engines and while out of the water so I could do the bottom I droped the rudder and changed props (and shortend the shaft so I could get the new-flex coupling on and off without pulling the rudder and thus be able to aline the shaft coupling/engine coupling). Back in the water and the new campbell prop is the wrong pitch or so it seemsed - still not sure about that one but that's another story. Long story short - wrong pitch (maybe).

So, Campbell and I talked. Beta marine and I talked. Campbell and Beta talked and they decided what I needed was a 16x8 not the 16x9.5 and that would fix my over heat problems.

So, the boat had to be pulled again. This time I'm smart. I shorten the shaft so the prop can be changed in the water. I'm thinking now. On a roll. Back in the water the prop made not 1 RPM difference and I still over heat. Aw! Sucks!

I've had the year from hell with a new engine that is too small, over heats and leaks oil. Aw! Shoot!

I've had it! Beta and I talk and they agree to take back their 37.5 hp that leaks oil and over heats and agravates the you-know-what out of me and give me a 43 for the difference in price of the 2. Fair, except now I have to go thru the whole engine installation thing agin including getting the prop right.

So, I remove the old new engine and while the engine is out of the boat pop the old new prop off and put on a Michagin wheel 17x12 which should be right for the new 43 hp. By-the-by its seems to be about right for the engine and boat.

So, this engine had to be moved a little further back in the engine room (missnomer) so it would fit becasue it was longer than the 37.5hp. And, you guessed it now I am back to square 1 with the shaft. I have to remove the rudder to change out the prop.

All that to say, I ain't taking the prop off just now & when I do I'll probably change the prop to the Campbell eqivalant of the 17x12 MW.

Funny how one inocent little statement triggered such a flood, huh? Sorry about that but I feel better anyway.

Fairwinds and Rum Drinks(and believe me I've had a few),

Vic

PS- One of these days I'll write up what I've learned on this project.
 
Vic,
I am sure that we can learn volumes from your experience. Partially based on your woes and partially because I have always belived that it is better to deal with the devil you know than to conjure up a new one. I have decided to rebuild(or replace with same) the perkins 4108 I have on the boat before we go cruising.While this engine is no longer in production, there are still thousands in service all over the world.
I am sure we will all benefit greatly from your endeavour and look forward to reading your post mortem on this project.

Best Regards
Jose
 
Hi,

I have just read this thread because I have some similar noise issues.
It occurs in fwd but not reverse, however mine is more of a varying grumbling sound above 1700 revs.

Getting back to the thread.... The sound as you describe it sounds like when you drill metal. ie. a high pitched whine / shriek, but in your case more constant. This makes me think it could be the cutlass bearing as you similarly have a metal shaft rotating in a metal surround.

I realise this has already been suggested but thought i'd try and add weight to the theory.

Trouble is you cannot check this by removing the propeller as the bearing could be affected by an unbalanced propeller or forces acting as a result of the propeller.

I would recommend changing the bearing, however, from the sound of it it's not an immediate failure problem and it'll still get you out of trouble when required.

Incidentally, it is likely you'll get less drag (and less gearbox / bearing wear) if you leave it in gear under sail. I didn't believe this either but have now seen test graphs in a magazine.

Well, enough rambling, I hope you sort it, keep us posted.

Cheers

Rob
 
Hi All and greetings froam a new member,

I too have had recient problems with a ringing squeel and previously a screach (but on my PSC34).
The screach was caused by a nylon bushing that adapted a 1 inch shaft to a 1.25 inch diameter propeller. The bushing extruded itself forward into the cutlass bearing and caused the screach which could be induced even by turning the shaft and pulling the shaft forward once the flange spacer was removed. The solution was a bronze bushing.
The ringing occured with a installation of a new longer shaft and cutlass along with a drive saver. I get it only in forward with the engine running at 1000 to 1400 RPM and 1600 to 2000 RPM. I dont get in reverse and it is largely gone with the helm all the way over, especially turning right. I also get it when sailing over 5 knots with the shaft free wheeling which rules out other engine stuff. Yes it sound like a wine glass ring, and sort of "modes" going from low to high RPM.
If you take the prop off the sound is not there. If I remove the driver saver the sound has gone away, at least for the first short run. Note that I had put on about 6 hours of running and tried various allignments hoping that it might be the cutlass.
As it turns out I might have 3 to 5 inches of shaft length after the cutlass (that is in the deadwood). It furthur turns out the the Propeller handbook says that there should be no more that 1 to 2 shaft diameter spacing, and the ABYC standard says not more than one shaft diameter. Looking at my previous (non ringing installation) the prop was within an inch of the cutlass.
Now you can read a bunch on the webb about ringing props but I and the prop shop think the problem is too much shaft length between the prop and the cutlass which is why removing the saver eliminated the ringing (at least so far).
Also I am told that a bad transmission thrust bearing makes more of a growl
Hope this helps
 
It sounds as though you have gerry-rigged the drive system of your boat. A proper prop should be installed on the drive shaft! By that I mean correct diameter and pitch. If the boat is in the water, you should consult a good diver to inspect everything outside the hull, both in gear and out while motor is running. By the way, what is the model of the Morgan?
 
Hi Jim,
The boat is a 1988 Pacific Seacraft 34, which is clearly not a Morgan but I thought the description of the symptoms and the results might be useful to people searching for propeller ringing.

The boat came with the propeller/shaft/bushing combination which was successfully motored roughly a thousand miles late last Fall before the screach started. I am pleased with the performance, fuel economy, top end RPM, and exhaust which supports that the propeller diameter and pitch are correct as well as meeting the recommendation for the engine. Hopefully the bronze bushing will prove robust.
The new shaft was lengthened with the thought of getting the propeller better centered in the cutout for better efficiency, and because I wanted to be able to butt the flanges dirrectly without the existing spacer or a drive saver. As stated in the last post I now believe we over did the length.

After the ringing occured with the new equipment and several attempts at reallignment and a dive, the boat was rehauled and inspected by the yard, an independent mechanic and myself. There was "no trouble found" which is to say the prop was tight and on correctly with the key in the right place, there was nothing wrapped around the shaft like monofiliment up in the cutlass, the diameters for the shaft and cutlass were correct, and it turned very freely. Initially I was concerned that the groves in the cutlass were somewhat blocked by the new bottom paint; but furthur clearing that out did not help the ringing, and I have had a good drip comming out of the new stuffing box since the new installation, which is to say water is clearly getting into the cutlass and shaft tube. By the way, we did put the boat back in the water and turned the shaft over the full range of RPMs in forward and reverse without any ringing present.

Overall I have no intent of cluttering the Morgan site with PSC stuff but it can be very frustrating an expensive to trouble shoot such problems and I personally did not want to sharpen the trailing edge of my propeller as suggested elsewhere on the webb.

It would be really interesting to know how some of the difficulties described in other posts were resolved.

Regards
Ed M
 
Addendum,
What I meant to say above is that we ran the boat in the water without the prop over the full RPM range, both dirrections, and the ringing was gone. Had the noise still been there one might have suspected the cutlass or other.

Ed M
 
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