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What are the symptoms of prop imbalance?


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As discussed in another thread I started, I've got new props on the new boat.  To the best of my inexpert ability to tell, it seems to be running great & making the right speeds & RPMs.

I've also noticed a bit of vibration that wasn't there before.  Spooling up, from just about anything above idle through about 2,000 RPM, there's a vibration, very rhythmic in nature, with a "frequency" (right term?) that seems proportional to the engine speed.  Above about 2,000 RPM it...  well, I don't know that it "disappears," per se, but it fades away into the background of the overall boat noises & vibrations.

On slow-down, it seems to manifest at pretty much any speed while the engine is slowing.  This I'd describe as a slight shudder.

 

Is this the description of imbalanced props?  How does one tell?

Is prop balancing in the repertoire of the dealer, or is that a specialty-shop item?

 

Thanks for any pointers, and the patience this group has shown for my noob questions!

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1 hour ago, Jughead135 said:

As discussed in another thread I started, I've got new props on the new boat.  To the best of my inexpert ability to tell, it seems to be running great & making the right speeds & RPMs.

I've also noticed a bit of vibration that wasn't there before.  Spooling up, from just about anything above idle through about 2,000 RPM, there's a vibration, very rhythmic in nature, with a "frequency" (right term?) that seems proportional to the engine speed.  Above about 2,000 RPM it...  well, I don't know that it "disappears," per se, but it fades away into the background of the overall boat noises & vibrations.

On slow-down, it seems to manifest at pretty much any speed while the engine is slowing.  This I'd describe as a slight shudder.

 

Is this the description of imbalanced props?  How does one tell?

Is prop balancing in the repertoire of the dealer, or is that a specialty-shop item?

 

Thanks for any pointers, and the patience this group has shown for my noob questions!

If you feel any type of vibration, take it to a shop that repairs props and have them test it, you don't need a dealer to do it, dealers do not repair props, cut out the middle man, and save money. 

Take it to the dealer, only if it is under warranty.  Denny.

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The test is easy. Run the boat on muffs, and while standing clear, drop the boat in gear at idle, and observe the drive for a rhythmic side deflection. If it's apparent than either the prop, or props are out of balance, or you have a bent prop shaft. Remove the prop, or props and use a dial indicator to check the shaft run-out. If it runs true, find a prop shop featuring Hale computer based balancing equipment and they will dial them in for you. It's surprising how far off they can be right out of the box, from the factory. The OEM spec is pretty wide for acceptability.  W

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44 minutes ago, Wingnut said:

The test is easy. Run the boat on muffs, and while standing clear, drop the boat in gear at idle, and observe the drive for a rhythmic side deflection. If it's apparent than either the prop, or props are out of balance, or you have a bent prop shaft. Remove the prop, or props and use a dial indicator to check the shaft run-out. If it runs true, find a prop shop featuring Hale computer based balancing equipment and they will dial them in for you. It's surprising how far off they can be right out of the box, from the factory. The OEM spec is pretty wide for acceptability.  W

+1 been there done that.  Denny.

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5 hours ago, ramoszx12r@comcast.net said:

Oh man I do not think I could that, I be to afraid to hit something. 

Actually it is pretty simple. First I pulled the prop and then ran the engine at an idle in forward, and held the end of a screwdriver at the end of the shaft, to see if there was any run out.

That checked out to be ok. Then I put the prop back on and while turning it by hand, (no engine running) I held the screwdriver at different points of the prop to see if any blades would hit it.

It is not high tech, but it will tell you if the shaft or any of the blades are bent.

I have a wooden tool box that I rest my feet on at the helm, and if there is the slightest vibration of any kind, it will transmit through that box.  Denny.

IMG-0384.jpg

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26 minutes ago, Denny said:

Actually it is pretty simple. First I pulled the prop and then ran the engine at an idle in forward, and held the end of a screwdriver at the end of the shaft, to see if there was any run out.

That checked out to be ok. Then I put the prop back on and while turning it by hand, (no engine running) I held the screwdriver at different points of the prop to see if any blades would hit it.

It is not high tech, but it will tell you if the shaft or any of the blades are bent.

I have a wooden tool box that I rest my feet on at the helm, and if there is the slightest vibration of any kind, it will transmit through that box.  Denny.

IMG-0384.jpg

Sounds good.

 

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2 hours ago, Phillbo said:

Or just take the prop to a shop to be balanced....... 

I do this first after I have hit something and then if it needs more then I feel I can straighten, I will take it to my local prop shop.  Denny.

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  • 2 months later...

EPILOGUE:  It took a while.  Between some unrelated work regarding the "we-owes" from the purchase along with some (very) minor delivery squawks, and our own schedule of using the boat & then getting out of Dodge for the season, the prop issue has only now been dealt with.

One of the "we-owes" was installing the trim tabs (God only knows why anyone would have ordered this boat without; but, they did, and we made it part of the sales contract to have them installed), following which the demo captain offered to take me out for some instruction on them.  That instruction turned out to be little more than "press this switch for up, and this switch..."; BUT, I was glad to have him along to demonstrate the vibration I was complaining about.  Particularly since the service tech who had lake-tested the boat said, basically, "Nope, nothing to see here!," I was eager for a second opinion.  The vibration was obvious enough that the demo captain agreed--so, they had officially recognized it now.  This was right before a long weekend, after which we were putting the boat up for the season.  Instead, we dropped it off at the service dock prior to leaving town.

Fast-forward about two weeks, and I got the following laconic response from the service manager:

Quote

PROPS needed to be rebuilt had bent blade and re-condition all in balance

I think that’s GREAT news on the props:  that’s about as much of a “smoking gun” as one could ask for, yes?  (The fact they needed to be rebuilt, a blade was bent, and re-conditioned—any one of which, particularly a bent blade, could/would cause vibration, yes?)  Won’t be able to test until Spring, but sounds like we’ve got this one licked...??

Once again, I have to ask you to forgive my ignorance, this is outside my expertise:  Does a “rebuilt,” “re-conditioned” prop which formerly had a “bent blade” imply a problem, either now or down the road?  Is such “good as new” (on my new boat) and will have the full life expectancy as if it were new?  Or am I starting from a degraded position? 

 

[Reminder for those following at home:  these are the third set of props I've seen on this boat.  My first test run, with FH-3s, I rejected the boat--the RPM was obviously out of whack.  They then switched to FH-4s, which made me happy with how the boat felt, and I bought the boat.  Later, having read the documentation, I realized the RPM was still not making manufacturer's specs, and they switched out FH-5s.  RPMs are now in spec, but the vibration was there.

  That vibration is now supposedly gone.  BUT, at what "cost" in the sense of what quality props do I now have...?]
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7 hours ago, Jughead135 said:

EPILOGUE:  It took a while.  Between some unrelated work regarding the "we-owes" from the purchase along with some (very) minor delivery squawks, and our own schedule of using the boat & then getting out of Dodge for the season, the prop issue has only now been dealt with.

One of the "we-owes" was installing the trim tabs (God only knows why anyone would have ordered this boat without; but, they did, and we made it part of the sales contract to have them installed), following which the demo captain offered to take me out for some instruction on them.  That instruction turned out to be little more than "press this switch for up, and this switch..."; BUT, I was glad to have him along to demonstrate the vibration I was complaining about.  Particularly since the service tech who had lake-tested the boat said, basically, "Nope, nothing to see here!," I was eager for a second opinion.  The vibration was obvious enough that the demo captain agreed--so, they had officially recognized it now.  This was right before a long weekend, after which we were putting the boat up for the season.  Instead, we dropped it off at the service dock prior to leaving town.

Fast-forward about two weeks, and I got the following laconic response from the service manager:

I think that’s GREAT news on the props:  that’s about as much of a “smoking gun” as one could ask for, yes?  (The fact they needed to be rebuilt, a blade was bent, and re-conditioned—any one of which, particularly a bent blade, could/would cause vibration, yes?)  Won’t be able to test until Spring, but sounds like we’ve got this one licked...??

 

Once again, I have to ask you to forgive my ignorance, this is outside my expertise:  Does a “rebuilt,” “re-conditioned” prop which formerly had a “bent blade” imply a problem, either now or down the road?  Is such “good as new” (on my new boat) and will have the full life expectancy as if it were new?  Or am I starting from a degraded position? 

 

[Reminder for those following at home:  these are the third set of props I've seen on this boat.  My first test run, with FH-3s, I rejected the boat--the RPM was obviously out of whack.  They then switched to FH-4s, which made me happy with how the boat felt, and I bought the boat.  Later, having read the documentation, I realized the RPM was still not making manufacturer's specs, and they switched out FH-5s.  RPMs are now in spec, but the vibration was there.

 

  That vibration is now supposedly gone.  BUT, at what "cost" in the sense of what quality props do I now have...?]

Sometimes brand new props from the factor have to be bent and balanced, mine did.

It did not feel right, so I took it to my local prop place and they said that it was out of balance.

So if it is balanced right, you should not have any problems down the road.  Denny.

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  • 3 months later...

Several years ago, I hit something and bent the prop a little bit. The funny thing is the boat went faster. I eventually swapped it and took it in for repairs.  

I don't have a toolbox under my feet but I always have my hand on the throttle or throttle housing which also transmits vibration. Vibration is a great communicator when something is going wrong.  

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  • 1 month later...

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