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3 Blade to 4 Blade change question

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  • 3 Blade to 4 Blade change question


    We currently have 3 blade aluminum 18" 23P on Bravo 2 drives 5.7L mercruiser. We are looking at getting 4 blade stainless steel 18-1/2 22P.

    What differences might we expect in terms of RPM and whole shot?



  • #2
    Should see a lil better hole shot and a tad drop in RPM
    When in doubt,Trim it out!!!
    Business Owner & Certifed Technician
    Boats I own & use
    20ft Javlin w/250 Junkrude
    17ft Bullet w/200 Merc (SOLD!!)
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    14 x 48 Drifter with 1100SS Merc


    • #3
      The hull, motor, prop size and design all factor in to how well a prop performs on a given boat.

      Unless your changing from one size to the next of the same brand and make of prop, all bets are off on how the change will react on any given boat.

      I went from a Evinrude 4 blade Stainless to a Mercury 3 blade stainless. Better hole shot. Higher top end and a better all performing prop.

      Your results may vary..


      • #4
        You might want to go to a 21 P 18” Dia to maintain your top RPM.

        Going down 1 in pitch while going up in diameter may not work out.
        Best regards, Ted . . . . Cape Cod, MA

        Current Boats: Formula 330 Sun Sport, O'Day Mariner Sail #3224, Sunfish
        Past Boats: Catalina 22 Sail #10531, Formula 242 Sun Sport
        Twin Mercruiser 7.4 LX MPI (0F802036, 039), Bravo 3's (0F806198, 199), Mercury 7.5 HP (1969), Johnson 4.5 HP (1980)

        My Boating Web Pages: http://www.tpenfield.com


        • #5
          Not a prop guy really, can only state experience. Disclaimer: Like stated, so many factors can affect the outcome.

          My boat was a 20-21 walk-around outboard. Fairly heavy with gear. I felt I had to run alot of RPM to remain on plane. I went from 3 blade Alum to a 4 blade stainless. Went down 1/2" in Diameter, and down 2 pitches. Only slight WOT RPM drop. But now I can remain on plane at much lower RPM, still good hole-shot, and no noticable top end difference. Really love it on my rig. Cant say enought about the difference.


          • #6
            My prop guy always says to drop a pitch when going to a four blade from a three. This is assuming that top end RPM is OK to start with.
            "Growing old is mandatory. Growing up is optional."


            • #7
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              I’d say you’d see better hole shot, similar rpm but a fairly substantial drop in top end speed and fuel economy