Prop Tune & Engine RPM

Discussion in 'Downeast Engine Room' started by JimRP31, Jun 26, 2018.

  1. JimRP31

    JimRP31 Captain

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    When I first bought my boat it had a lot of vibration at all RPM's. I had my Prop tuned this winter. I have a Yanmar 6LYA-STE. I filled the tanks up and too the family for a spin. It was a little choppy but no real waves. I think the prop tuner got it right. But I am open to opinions.
    RPM's Speed in Knots
    2000 10
    2500 13.9-14
    2700 15.2
    2800 16
    2900 16.8
    3000 17.6
    3100 18.3
    3200 19 WOT
     
  2. Gurryman

    Gurryman Captain

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    That motor is rated at 3300 RPM, you need to see 3400 at WOT :(
     
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  3. duckhunter

    duckhunter Senior Member

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    I'm with Gurryman. Better to be underpropped by 100rpm - especially at the beginning of the season, with a clean bottom and fresh prop - than running right on the ragged edge. Turning 100rpm under rated is not a recipe for longevity.

    Did it cure the vibrations? If so, that's a win, but I'd see if the prop guy would take out a little pitch for you.
     
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  4. fortier256

    fortier256 Senior Member

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    Agreed on minimum 3400 WOT loaded. That number comes from Yanmar. Be sure to use a photo tachometer at least verify your boats tachometer is correct.
     

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  5. powderpro

    powderpro Captain

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    Maybe you already have, but verify your throttle position is 100% at full throttle. Would hate to see you repitch the prop if the prop isn't the problem.
     
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  6. BillD

    BillD Captain

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    I'd take 2.5" of pitch out of the prop "after" you've verified "full throttle advance" 100% and that the WOT you measured is via "photo tach".

    For long term engine life.....Better to be "over propped" than "under propped". It's all about "engine load" and keeping EGTs below max spec.

    Just my 2 cents.
     
  7. JimRP31

    JimRP31 Captain

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    All good points.
    Duckhunter it did cure the vibration. I did not want to try WOT until I cured the vibration. BillD, Fortier256, Gurryman & Powederpro all good point. I agree with your assessments that I am overpropped at the moment but I did not give the prop guy any RPM guidance (due to vibrations) we agreed to a best guess. Gurryman, I will confirm I am at the full throttle position and get a photo tach to confirm RPM's. I am going try a few more runs over the summer and pull the prop when I haul the boat in the fall. I will say the engine sounds the best and runs smoothest at 2900. I am still learning.
     
  8. steveinak

    steveinak Captain

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    Don't ya mean better to be under propped ?? for less engine load ??
     
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  9. traditions

    traditions Captain

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    I think you got that Bass Akwards Bill
     
  10. powderpro

    powderpro Captain

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    After 5,500+ posts, he was bound to get something backwards.:D
     
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  11. BillD

    BillD Captain

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    ya backwards....sorry.....


    The 6BTA 370 in the 25 T Jason is propped to reach 3250 rpms.
    The 370 is rated 355bhp @3,000 rpms.

    The mechanical governor, under load, will not let the engine spin up to 3250 so you'd
    never see true WOT on the tach. I've photo tached @ 3180 ish. WOT

    How could I help verify my 370 was really under propped to 3250 WOT if I could never "see it" on a tach?

    Any takers on the question ? :cool:
     
  12. 05bill

    05bill Captain

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    I have same boat , same motor, RP put 22 x 22 prop on. Yanmar tech at splash said all was fine. I reached 3300 rpms. I had prop repitched to 22 x 20 .I now get 3450 wot, a little under propped but that is fine with me, piece of mind.

    I do not run that engine past 80 % of wot rpms !!! Jim 2900 ?


    Bill
     
  13. fortier256

    fortier256 Senior Member

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    That’s right where you want to be. You would probably be able to run at the Yanmar posted continues rating (3200?) if you wanted to without any ill effects. It’s the load / EGT that is the killer not RPM.
     
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  14. Genius

    Genius Captain

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    What is High Idle RPM spec for the engine?
     
  15. 05bill

    05bill Captain

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    Fortier 26, I hear you but I am a conservative guy,3200 I would be a nervous wreck.

    Genius the spec says 3300 , but we all know it should be higher, to 3400-3500.

    Fortier do you know the pyrometer range , for this engine prior to turbo ? I know but just checking .
     
  16. 05bill

    05bill Captain

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    Oh Genius that number is 3700 rpm. Sorry I didn't see idle rpm.

    Bill
     
  17. Genius

    Genius Captain

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    05Bill, I was responding to BillD's post on the cummins.

    I'd have no problem running your Yanmar at 3200, sounds really good at that speed. Like fortier256 says....
     
  18. fortier256

    fortier256 Senior Member

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    I do not have the info for your motor. However my 4LH manual calls for less than 1200f at WOT.......Before the turbo.
     
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  19. Beamie

    Beamie Senior Member

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    Well, a good accurate charge air boost pressure gauge will tell allot about load when compared to test bed results.
     
  20. JimRP31

    JimRP31 Captain

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    Bill, just to compare I have a 22" diameter LH that the previous owner reduced to 21. My Pitch is 20.8. I am over-propped at this point but I don't want to take the haul the boat until the fall. I can comfortably run at 2900-3000 for this summer. I still need to confirm I am getting full throttle and get a photo tach. I will say once I get it dialed in I will run it 3200 without a worry.

    Fortier, forgive my ignorance but what is EGT?
     

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