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Thread: how to figure speed pitch to RPM

  1. #1
    lnsper
    dose any one know how to figure speed with pitch to RPM
    I have a 89 242Eliminator edge with a 24 pitch bravo 1 4 blade
    turning 5100 rpm
    thank Shawn

  2. #2
    You Te
    RPM X pitch...... divide gear raito...... divide 1050 X slip = speed
    EG......... 11000 X 24 = 264000.00 divide 1.87 =141176.47 divide 1050 =134.46 X .90 = 121.02 MPH.
    .90 is 10% slip .95 is 5% slip and so on.
    You Te

  3. #3
    celeb1
    Prop pitch X RPM
    divided by
    gear ratio X 1056
    this will give you your theoretical speed
    take your actual speed and divide that by theoreticle speed and that will give you a number like .89 for example which would indicate 89% efficiency or 11% inefficiency (slippage).

  4. #4
    Dave C

  5. #5
    Snowboat
    I think this one is easier.
    RPM X PITCH X GEAR RATIO X SLIP X .0009469 = SPEED
    6,000 X 15 1/2 X 1.18 (18'S IN A V DRIVE) X .85 (15% SLIP) X
    .0009469 =85.48
    Sounds about right for a nice flattie, not a hydro.
    Works for Mercruiser, only the gear will be .25, .50, .65, etc.

  6. #6
    burtandnancy
    I always liked the following:
    rpm x pitch x ratio* x .00094697 = theoretical speed. Then you have to find your slip factor and multiply it in. 10% is super, 25% for sleds.
    *a V drive usually give you overdrive, but all stern drives are under driven.
    A radar gun or GPS will pretty well peg your slip factor...

  7. #7
    lnsper
    thanks every one now i need a gps

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