Tohastu 20 hp 4-Stroke

Discussion in 'Prop Shop' started by islander1225, May 1, 2012.

  1. islander1225

    islander1225 Well-Known Member

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    Hey guys i have a 05 classic with TSG electric Jackplate, I have recently went from a Merc 25 hp 2strk to a Hatsu 20 Hp 4 stroke, I finally installed my tiny tach and bobs cavitation plate. Here is my dilemma. The stock prop on the motor is like 9.8 pitch, With the jackplate all the way down i am hitting 6100 rpms, but when i raise jackplate i have reduce throttle to keep from going over the 6100 due to the rpms going up when i raise jackplate. Also with the merc i could lift jackplate all the way up with no ventilation at all i could even take full turns with it all the way up, with the new motor i cant even get it half way without major ventilation, What i am trying to do is be able to run jackplate all the way without ventilation and under 6100 rpms, which prop should i go to?


    Alex
     
  2. Brett

    Brett > PRO STAFF <

    If it was mine, I'd be trying a cupped 12 pitch.
     

  3. islander1225

    islander1225 Well-Known Member

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    I talked to powertech today and they told me to go to a 8 pitch??? he cant be right can he?>
     
  4. Brett

    Brett > PRO STAFF <

    8 pitch on a 20hp /noe ;D
    Y'er already tapping the rev limiter.
    Time to increase pitch and cup to get you back down to 5500 to 5900 rpm.
    An 11 or 12 pitch with cupped blades will do you better.
     
  5. Flyline

    Flyline Won &quot;Do More With Less&quot; Award!

    Talk to Marc at Powertech.....get a 3 blade s.s SRA 11” pitch with standard cup.
     
  6. islander1225

    islander1225 Well-Known Member

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    What do you guys think? a 4 blade or 3 blade with cup?




    Alex
     
  7. Brett

    Brett > PRO STAFF <

    My vote's for a cupped 3 blade.
    You aren't trying to hole shot a tunnel hull.
     
  8. islander1225

    islander1225 Well-Known Member

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    10-4, i mainly would like to just be able to lift my jackplate again, but this ventilation is killing me,

    i tried a 4 blade 11 pitch and and lost all ym top end and still had ventilation problems.


    Alex
     
  9. islander1225

    islander1225 Well-Known Member

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    Also i forgot to mention that i did try out the 9.25 dia x 11 pitch 3 blade, I was able to lift the jackplate some while staying inside my rpm. So would i need to go with a 12in pitch 3 blade powertech? or higher? With my jackplte i have about 4 in of lift, it goes high lol.



    Alex
     
  10. Brett

    Brett > PRO STAFF <

    Only way I know to determine the correct answer is to test it.
     
  11. islander1225

    islander1225 Well-Known Member

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    I can bring the boat and all the props i have down to palm coast if need be, i really need to get this figured out, i fish a alot of shallow water and not being able to lift the jack plate is killing me lol.


    Alex
     
  12. Brett

    Brett > PRO STAFF <

    Sunday morning, Herschel Park ramp... :-?
     
  13. islander1225

    islander1225 Well-Known Member

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    Where is the Herschel Park ramp at? I will be there.





    Alex
     
  14. Brett

    Brett > PRO STAFF <

    Quiet ramp, rarely busy, great for testing and adjusting

    http://www.flaglercounty.org/facilities.aspx?page=detail&RID=10
     
  15. islander1225

    islander1225 Well-Known Member

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    Sounds good, what time do i need to be there? I am free all day.




    Alex
     
  16. Brett

    Brett > PRO STAFF <

    Pick your time, I live 10-15 minutes away, depending on the line at my coffee stop.

    This time of year I'm done fishn' by 8:30 am.  ;)
     
  17. islander1225

    islander1225 Well-Known Member

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    I can be there as early as you need me to be. Is 7 cool?



    Alex
     
  18. Brett

    Brett > PRO STAFF <

    Time can be decided on Saturday evening, pm sent
     
  19. evanslmtd

    evanslmtd Well-Known Member

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    Alex
    A few years ago I had a Classic (with a manual jack plate) that I put a new 20HP Hatsu motor on (great little motor).
    After break-in, I started fooling around trying to find the correct prop. Below are some excerpts from my test log:
    05/07/10 – Ran boat to test the stock Prop (9.25X10) that Soles Marine put a heavy cup in. Ran in a light chop (2”-3”) with a light load.
    Jacked up 2”, I saw 27.1 MPH at 6050 RPM (Good hole shot and turns)
    Jacked up +1/4” (21/4” high), I saw 28.1 MPH at 6090 RPM (Good hole shot and turns)
    Net increase in speed, 1.6 MPH/Net decrease in RPM -192.

    06-10-10 - Wind 10-15 with a 1’ chop
    Jacked up 1” w/ Aluminum prop saw 28.2 MPH @ 6150 RPM
    Jacked up 1” w/SS prop w/cup, saw 26.2 @ 5700 RPM tries to blow-out coming out of the hole. Good on turns.
    Jacked up 3/4” w/SS prop, saw 26.7 MPH @ 5690 RPM no blow-out on hole shot or turns.
    The SS wheel I went with was a Power Tech SRT 9-1/2”X10 SS wheel with extra cup.
    Hope this helps you find your prop.
     
  20. islander1225

    islander1225 Well-Known Member

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    Thanks for the info Barry, My prob is i am running an elctric jackplate that has 4 1/4 in of travel, with an 9.25 x 11 pitch i can raise jp up almost half way with no issues and still performs well, I am looking to go higher, when i go high my rpms shoot through roof and and I have ventilation. I am gonna get with brett here soon so he can see what it is doing so he can make some suggestions on what i need.

    Alex