A singing propeller

The boatyard says I have a "singing" prop.* To me, it sounds like an*"up-and down"*whine which occurs between 1000 and 1400 RPMs.* What do you believe can be the cause, from the most to least likely cause?

Not in any order, reasons I have heard for this are blades out of true, edges too sharp, blade pitches not all equal, blade widths or lengths not equal. If you don't have any vibration in the boat the blade differences will be very slight but it apparently doesn't take much to start a high-pitch vibration. The trailing edges of the props sometimes seem to be the culprit, too.

Transmissions can whine, too.

Thanks, Marin.* Your comments are consistent with the boatyard's initial verdict.* They're proposing the propeller be pulled and be reworked (edges and such).

Not the cutlasss bearing perhaps?

Doc wrote:
Not the cutlasss bearing perhaps?

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*Why not?* But it has only been*used for 50 engine hours.

Had this occur on several boats.

It's usually caused by the trailing edge of the blades being too fine. I've fixed them in the past by squaring off the edge -*just a little*- with a fine stone. Sounds like the yard is onto it.

what tune does it perfer to sing? probably rap I had one that sang the blues, i had to replace it as it made my motor sad

Better singing than screaming all the time for no reason, I suppose.

I have a propeller question some one might be able to advise me on.* I have a vibration that shows up at 1500 rpm and persists to 1650 rpm.* Since we almost always run at 1250 - 1350, it's not an issue.* There are new cutlass bearings and the shaft has theoretically been properly aligned.* My questions are:

1.**Would an imbalanced prop have any negative effects when run in the sweet, no vibration range?* Say on the cutlass bearings?

2.* If removed and balanced, how likely is it that a vibration shows up at another rpm range?

3.* The prop was tuned by the PO and this range vibration has been there since I bought her in 2003.* How likely is it that the prop wasn't balanced properly, or is this likely to turn out to be a function of factors other than prop balance?

4.* I asked a very experienced CAT mechanic about this, and he said that 3306s all vibrate under load at certain RPM ranges.* He said that they had spent a lot of hours on engines trying to balance them to no avail.* Does this make sense?* Sunchaser, I think you have experience in this area, correct?

I know I can get ideas on these from a prop shop, but any comments on your own experience in this area would be welcomed.

A good prop shop*can check the prop for balance, thickness and pitch true for each blade. With all the possible issues you raised it can be a guessing game if the prop checks good. Rudder vibration at certain prop exit velocities can cause some rumble as well as motor mounts, different durometer rubber in the struts etc*--------.

With 20 or so additional tons of cargo (herring or cod) in* your vessel maybe it wouldn't rumble at 1500??

sunchaser wrote:
A good prop shop*can check the prop for balance, thickness and pitch true for each blade. With all the possible issues you raised it can be a guessing game if the prop checks good. Rudder vibration at certain prop exit velocities can cause some rumble as well as motor mounts, different durometer rubber in the struts etc*--------.

With 20 or so additional tons of cargo (herring or cod) in* your vessel maybe it wouldn't rumble at 1500??

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*Thanks Tom.* There are so many variables I guess it could turn out that after balancing, the rumble still remains.* My worry is that it would move to an rpm I actually use.*

I'll take your suggestion though and move the barrels of whale blubber from the master stateroom to the head and see if that helps.....

Delfin wrote:3.* The prop was tuned by the PO and this range vibration has been there since I bought her in 2003.* How likely is it that the prop wasn't balanced properly, or is this likely to turn out to be a function of factors other than prop balance?

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When we bought our boat in 1998 it had no vibration evident in the driveline at all.* We ran the boat this way for some nine years until we were advised by a prop shop that our props were "worn out."* Assuming we had to buy new ones I inquired among friends in the marine diesel manufacturing business and in the San Juan islands landing craft haulage business as to what they felt was the best prop shop in the area.* I got the same answer from all of them so that's who we went to.

Armed with the data the shop told us they needed to determine the right props for our boat, we took the old props to them assuming we would be buying new ones.* They took one of the old ones into the shop and checked it and came back and said the prop was fine but it had been horribly set up by whoever did it last. This would have been someone in the SFO Bay area before we bought the boat.* One blade on one of the props wasn't even moving water at cruise rpm.* Blade lengths were slightly different--- all sorts of problems.*

But.... none of this was evident when the boat was running.* No vibration, no clue at all that the props were a mess.*

So yes, it is very possible that even if a PO had your prop worked on, there is no guarantee it was set up correctly.* The folks at the shop we used could tell from our props the method that had been used to set them up previously, and they said it was a less than ideal one.* So instead of buying new props at some $1800 each they completely reworked our old ones for $350 each.

So Tom's suggestion of taking the prop to a good prop shop is a good place to start if you suspect a problem with the prop.* They may even be able to advise you from a verbal description if what you are experiencing could be related to the prop or is more likely coming from some other source.





-- Edited by Marin on Saturday 3rd of September 2011 12:14:40 PM

Thanks Marin.* Our prop is 44" and weighs a bit, so I wonder if it is possible for an in situ examination to yield guidance on whether to remove the prop for re-working?* I'll talk to a shop.....

Which shop did you go to that you were happy with?

Marin took his to Kruger & Sons. I went there once and would not go back. I'd recommend Tacoma Propeller. Since you have a large propeller you will probably get better service at Kroger. Some propeller services have pet agenda's like lots of rake. Some don't have computer equipment. Would you have a mechanic balance your car wheels w a bubble balancer? I would and you almost certainly not be able to feel the difference at 100mph. Same w propellers. Unless you hit something I don't think many propellers need to be reworked. That is if you've got it pitched properly at WOT. Also I don't think propellers are very susceptible to resonance that would produce more or less vibration at various rpm. A propeller vibration from either pitch or weight problems should vibrate less at low rpm and much more at high rpm. What does vibrate at spefic speeds,rpm or frequencies in my opinion is resonance in the boat. Hull bottoms, bulkheads, decks, cabin tops and many other flat or fairly flat surfaces that can be excited to vibrate. Wood boats are the least likely to be resonant. Metal boats probably the most likely but resonant structures can be made non resonant by adding weight or stiffness. If a bulkhead vibrates at the engine rpm of 1500 attach something heavy and strong to it. Don't attach the fix in the middle. Then you have just doubled the resonance frequency. But depending on other variables that may be OK or it may cause other things to vibrate that were still and quiet before. Attach the fix at about 30 to 40% of the span. Anyway I think the singing propeller is the trailing edge and the 1500 to 1650rpm vibration is in the boat structures. Just say'in.

Next week, I expect to have the Coot hauled out and: have the propeller pulled and reworked; have the bow thruster examined (it's locked); and replace the chain-locker-drain-exit fitting replaced.* Anticipate these will be subjects for future discussion.

Thanks Eric.* From their website, Tacoma Prop doesn't doe anything larger than 35", so Kruger seems to be the best option, as others have been kind enough to recommend by PM.

I think you might be right about resonance.* I sprayed the empty hull with QuietShip and lined her with acoustical cork to address that, but I doubt there is any perfect fix.* Thanks again!

nomadwilly wrote:
Marin took his to Kruger & Sons. I went there once and would not go back.

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I'm not sure what experience Eric had at Kruger that soured him on them but our experience and the experience of the several other people we talked to--- including the operator of one of the barge services in the San Juans-- at Kruger has been outstanding.* Prompt, courteous, they even gave us some drilled setscrews for our new shaft couplers for free when I found that the shop that had supplied the couplers (not Kruger) had installed non-drilled setscrews.* And from the look of the props in their yard, they work on some pretty big stuff.* I asked what the largest prop they could accomodate was and they told me but I've forgotten.* But they had props there that looked like they came off commercial tugs or something.


-- Edited by Marin on Tuesday 6th of September 2011 11:10:26 AM

Marin,

Kruger gives good service to those that bring big propellers to them but they think it's beneath their dignity to work on smaller props (18" in our case). If you've got a tug or seine boat Kruger's the place to go** ...and probably for Carl. I didn't like their attitude and I (as I recall) don't think they did a thing to my prop. But I paid.

nomadwilly wrote:
Marin,

Kruger gives good service to those that bring big propellers to them but they think it's beneath their dignity to work on smaller props (18" in our case). If you've got a tug or seine boat Kruger's the place to go** ...and probably for Carl.

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Well, everyone will have different experiences.* But the props on our GB are 24" and Kruger was delighted to deal with them.* In fact, as I've related before, we went into Kruger expecting to have to buy new props for about $1800 each.* We had been told by another prop shop that our props were "worn out."* Kruger checked them and said, no they were not worn out but they had been horribly set up by whoever did it last (prior to our buying the boat).* They said they'd be happy to sell us new props, but for $350 each they could completely rework and rebalance our existing ones.* So that's what we had them do.* Considering what they found was wrong with our props, they did a hell of a lot of work for their $350


-- Edited by Marin on Tuesday 6th of September 2011 11:29:02 AM

The Coot is going*"on the hard" for the next several weeks for work on propeller, thruster, chain locker drain, etc.





*

Where did you pull her?

Giggitoni wrote:
Where did you pull her?

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*KKMI in Richmond.* Selected because they're the local John Deere dealer so as to replace engine sensors and fix oil leak at water pump (pump to be replaced). Other issues kept "popping up."

Good timing.* I'm taking a two-week transatlantic cruise in a couple of weeks.* Hope things will all be "bettah" on my return.* Fortunately, that cruise will cost less than a couple days' work at the boatyard.


-- Edited by markpierce on Thursday 8th of September 2011 12:38:06 AM