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Thread: what prop ?

  1. #1
    Join Date
    Feb 2006

    what prop ?

    Hello guys

    I,m a newbie here ,and like to say hello.
    I,m from Europe ,Holland and have a 28 Sonic with a single Yanmar 370 hp diesel (6LYA-stp)
    I,m having some troubles with finding the right prop.
    I use a 1,50 :1 XR bravo 1 ,max rpm engine is 3500.
    First time after the conversion from a BBC to th Yanmar ,I used a 28 bravo 1 labber,I have never had so much prop slip seen ,like 20-25 %,cause i did 3500 rpm and barely 36 mph.
    So I used a 30 bravo labber,and it was almost the same ,I could hardly see any difference ,same rpm ,same speed.
    with both props it wasn,t completely planed ,it felt like a halfglider,it wasn,t flat running at all at wot.
    Strange thing was I pused it into plane ,and almost directly when the turbo charger came in, the rpm needle was at 3500 rpm and never came back ?it stayed there at 3500 rpm all the time ,(with the 28 and the 30 labbers)
    I could easy take the throttle back to 3/4 ,and it still was in the limiter at 3500 rpm.
    Forgot to mention ,the trim was all the way in ,if trimmed up a little ,things where worser,slower speed,and more bow rise .

    Then i tried a stock 28 bravo 1 ,and this felt much much better,now she,s running flat,and 42-43 mph.
    still i hit the limiter at 3500 rpm,and trimming up would make no difference ,cause I was at max rpm.

    Anti ventilation plate is +- 1 inch above the bottem.
    The weight of the Yanmar is 1100 lbs.
    Torque is 800 ft/lbs at 2200 (so I take it easy on the xr)

    Am I using the wrong type prop ?
    Do I better go with a Hydromotive P5X ?
    Or a Maximus ?
    Or do I have to turn the propellor faster with less pitch to be more effective ?
    I can borrow a 1,36 :1 ,and a 1,26 : 1 just to see what happens.

    Has anyone here an idea whats going on with my boat ?

    I have no comparison ,as I bought the boat with no engine .

    thanks A.J

  2. #2
    My Boats:
    1982 Eliminator Offshore
    Join Date
    Apr 2007
    Martinez, CA
    You seem to have the same problem as me. I just added a thread asking anyone to help with my prop selection also. If anyone gives me good feedback, I will pass onto you.

    Good Luck Kevin .

  3. #3
    My Boats:
    2003 Joker
    Join Date
    Mar 2002
    Boydton Va.
    Call Throttle-Up Props

  4. #4
    My Boats:
    Donzi 27 ZX... 500EFI .....With a little Boost
    Join Date
    Jun 2004
    Quote Originally Posted by chippin it View Post
    sounds like you need to try the 1.36 and the 30 pitch and go from there.A 5 blade wheel should help the slip.
    with the torque peaking so low you need a lower gear....a 1.50 will not work well with the set up you other words you need to spin a prop the same rpms @ 3500 as you spin a BBC prop @ 5000 to see any benifit here....does this make is all in the gearing on a diesel.


  5. #5
    Join Date
    Feb 2006

    prop gearing

    Thanks for input guys.

    Ok that leaves me with a 1,26 :1 to come closest to a BBC that turns 5000 rpm with 1,50 : 1.
    Mine will turn 2777 with 1,24: 1
    a BBC will do 3333 rpm with 1,50 : 1.
    I,m going to try it what happens as soon as the weather clears up.

    What is the biggest diameter prop that should fit my need ?
    I thought Merc said 16 inch max for a bravo 1 ,but do they make props so big ?

    What pitch would be used if you have a Sonic 28 with a 454 magnum ? assume it has 1,50 : 1 ,that way I can maybe find what pitch to use if I calculate these numers .

    I,m aware that my boat is not going to win any high speed awards,but I was hoping to see 50 mph with my engine/drive set up

    Do you guys think thats possible ?

    thanks A.J

  6. #6
    Registered evaluex's Avatar
    My Boats:
    Join Date
    Feb 2004
    Your numbers & too big pitch props don't make sense

    Last year Powerboat Mag tested 3 Eliminators 28 XP
    1 with the 496 HO which did 68,2 mph @ 5000 rpm
    1 with a 350 carb/ 250 HP => 48 mph
    Last one with a Yanmar 6LPA-STP / 315 HP coupled to a Bravo 1 X drive, 1.5 gear ratio spinning a non labbed Bravo 1 4blade 24P @ 4000 rpm giving a decent 52,8 mph

    If wanted, I can send you copy of this article, just let me know

    Downgearing could be an option, although Bob Teague always stated to run the highest gear ratio until you run out of prop pitch...But if you have those drives available, always worth a try.

    I certainly wouldn't start with labbed props, you'll need all the cup and bite of your prop to get this boat moving. Your high torque diesel engine will love the big Maximus 5 blade

    just my 02 cents peter nordic

  7. #7
    Join Date
    Feb 2006


    It would be nice to try a 26 or 28 pitch maximus with the 1,26 :1 gearing,just to see if I can get this heavy weight champion moving.
    First I am going to try a 1,36 with the 28 bravo 1 stocker.

    thx a.j

  8. #8
    Registered evaluex's Avatar
    My Boats:
    Join Date
    Feb 2004
    Quote Originally Posted by stirling View Post
    It would be nice to try a 26 or 28 pitch maximus with the 1,26 :1 gearing,
    We do have a 26P Maximus available in our prop test program

    Just let us know if we can be of any help

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