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26' project. Perkins jackshafted to ??? Need some help

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  • 26' project. Perkins jackshafted to ??? Need some help

    I am new to this forum as well as to marine diesel engines for that matter. Well, i got refered here from other forums and they told me some of you guys have sort of the same setup am after.

    Well, I have a 26' center console Proline that has a 10' beam. Its a project. Had twin 225hp Yamahas on a bracket. I sold the bracket and yamahas and bought me a Perkins Range4 M275ti .

    My goal: Install the engine under the console. Have a jackshaft run from the engine to the outdrive. Now, everyone tells me this engine will destroy most bravo outdrives, so a friend told me to just go straight shaft.

    Does anyone here have a similar setup? I need all the help and knowledge I can get my hands on. ANy help on the subject would be greatly appreciated.

  • #2

    Other than your perkins what do you have to work with?

    Do you have a jackshaft, or outdrive?

    Did the Perkins come with a transmission.

    Let me know what you have.



    • #3
      I posted this a long time ago. I have changed the plans for the boat. I no longer want to go with a lower unit (herd too many horror stories). I am looking more for reliability so am going with a straight shaft.

      I have done lots of work and have the stringers done, and the floor ready to be thrown at it. Am still missing the transmission and drive plate for my perkins (Range4 M275ti) 275hp. I already have 2 shafts one longer than the other but both are 1 1/8" S.S and also got a S.S rudder with seastar hydraulic system.

      My questions now are, What kind of gears do you guys think i should go for? prop size? what would be the top speed of this thing? and most importantly ( i still dont get) What angle should i give the shaft? and how do i go about the shaft tube?

      Remember it was an outboard boat, so i dont have a shaft tube. How does this work?

      Any help would be greatly appreciated!


      • #4
        Shaft Angle

        You will need to determine how much propeller diameter will be required to push this boat.

        Once that is known you establish the propeller location. The engine will need to be at or near the center of gravity. Add the length for your down angle transmission. Now you have the transmission output flange location and your propeller location. You can drill a hole in the hull and install a round fiberglass tube at the exact angle of your shaft or you can purchase Shaft logs that bolt to the hull. ( You may want to read Inboard Motor Installations Witt/Hankinson

        I would try for a 7 degree shaft angle. As you increase the degree of angle the thrust developed by the propeller is directed down instead of back. This reduces speed and increased the bow angle of the boat.