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Prop choice for Chaparral deckboat

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  • Prop choice for Chaparral deckboat

    I bought a 2004 Chaparral Sunesta 236 deckboat with a 5.0 fuel injected Merc. When boat was clean and I put in the lake with just me, I got 45 mph with 4600-4700 WOT with the new 4 blade Michigan Wheel Vortex 14 1/2 x 18. . Now that it's been in the water over a month and has scum on it I am getting WOT of 4000-4200 , 38-40 mph with 4 people in boat. Barely pulled me out of water on slalom ski. It was a real fight.
    Thinking I should change prop for skiing. Should I stick with 4 blade and go to 17"? Looking for some advise on what's best.
    Also, how do I determine what gear ratio is in this Alpha One Gen II?

  • #2
    Clean the hull . . . Sure, try a 17" pitch 4 blade.
    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


    • #3
      2nd on cleaning the Hull

      Even with the hull clean you were at the lower end of the WOT rpm range which is 4600 - 5000, so you are over propped when loaded. A 17" might be your cruising Prop as it will get you a couple hundred more rpms, or possibley a 16"

      You might want to try a 15 when skiing, a 23 ft boat is pretty big load for 5 liter when trying to pull up a Slalom Skier

      The gear Ratio is listed on the Decorative Band on the Upper Gear Housing on the Outdrive

      Myself, I would want a 6 or 7.4 liter in something that size, Nice looking boat
      Last edited by jimmbo; July 4th, 2019, 04:01 AM.


      • #4
        I would drop the pitch (to help get the engine in it's power band as quickly as possible) and stay with a 4 blade because of the size of the boat, and because you are looking for some low end performance (vs. emphasis on how fast it will go).


        • #5
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          Thanks for the input. However, I always put my boat in the water in May and it stays in until October. A clean hull only lasts a week or two. I guess I can drop down to a 17". Would a 5 blade be better?