Proper Prop for my 15'4" with 15 HP

Discussion in 'Prop Shop' started by zeneb, Oct 12, 2012.

  1. zeneb

    zeneb River Hawk 15'4" 15HP Evinrude / 15 HP Merc

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    I've got a RiverHawk 15'4" and am currently running an 84 OMC 15 HP on it. I will be adding a Stingray Jr. to it shortly. I will also be adding a grab bar to it, moving my weight up slightly.

    Currently I have my battery, small deep cycle, right in front of the front seat. I have my trolling motor, 55 lb thrust, mounted in the back. My gas can is just in front of the middle seat. My weight is 150. In the current config, I get 21-22 MPH depending on if I have the pin in the bottom or second slot. Bottom slot is slower, but the boat rides better. Second slot moves the water line from middle to half way between middle seat and rear seat. I've got a 1.5" riser on now which has the cavitation plat right at the bottom of the boat.

    Probably more info than you needed, but I want to know what is a good prop for that setup to gain more top end speed. I'm willing to shim up the riser some if needed, but need to have at least the 1.5" to run where I run. There are a couple of spots on the river where that extra 1.5" is the difference between hitting bottom and flying by. I'd like to get it tuned in before I through bolt the motor.

    Hooching
     
  2. Dillusion

    Dillusion devilray snob

    I had a merc 15 on my gheenoe 15.4 and I tested, 8, 9, and 10p props. A 10p with a slight cup was the best.
     

  3. zeneb

    zeneb River Hawk 15'4" 15HP Evinrude / 15 HP Merc

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    I just checked and the current prop is a 9-1/2 X 10.
     
  4. Dillusion

    Dillusion devilray snob

    Yeh.

    Mine stock was 9.25x9
     
  5. zeneb

    zeneb River Hawk 15'4" 15HP Evinrude / 15 HP Merc

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    so, is that about right then? How will cupping affect the prop?
     
  6. Dillusion

    Dillusion devilray snob

    Depending on how much cup you have done...a drop in RPM from 50 to 200

    But more water is directed back into the motor area instead of shooting outwards so it will help you trim the motor up slightly more.