Prop question

  • Jonesy
    Posts: 1148
    July 21, 2015 at 12:01 pm #1555706

    My boat 70hp 2 stroke evinrude currently has a 17 pitch prop on it. Boat can hit 36mph @5400 RPMs. It takes a lot of trim work to hit 5400 rpm’s however. I see my motor redlines at 6000 rpm so I am looking at dropping to a 15 pitch prop to hit the 5600-5800 range in RPM. I know this will help my hole shot but what do you think it will do to my top end? Am I crazy in thinking I might actually pick up a mph or 2? My thought behind that is that currently I am not hitting peak power numbers because I am not able to get the RPM into that range.

    FishBlood&RiverMud
    Prescott
    Posts: 6687
    July 21, 2015 at 12:24 pm #1555711

    You’ll probably hit 5800 rpm but lose a mph or two.

    I have a 70hp and replaced my 17 with a 15 this spring. Monday i put my 17 back on just because i’ve had the motor tuned up since removing it…the 17 will come off once again and become the spare as i enjoy the hole shot of the 15 more.

    Jonesy
    Posts: 1148
    July 21, 2015 at 12:28 pm #1555713

    Thanks for the reply. Bummer about losing top end. I already find myself wishing I could hit 38. I do think I would enjoy the better hole shot though

    wimwuen
    LaCrosse, WI
    Posts: 1960
    July 21, 2015 at 12:38 pm #1555716

    Can you raise the motor a hole? That might help you get some more RPMs out of your 17, and maybe some speed.

    Jonesy
    Posts: 1148
    July 21, 2015 at 12:42 pm #1555717

    I might be able to raise it. I know I had it raised last year so its on the 2nd hole I believe.

    FishBlood&RiverMud
    Prescott
    Posts: 6687
    July 22, 2015 at 7:55 am #1555839

    You want your cav plate withing a 1/2″ of level with the bottom of your transom. YOu’ll lose performance if you go more in either direction.

    eyekatcher
    Lakeville, MN
    Posts: 966
    July 22, 2015 at 1:12 pm #1555908

    There are a lot of variables in props.
    Propmann is an expert in this.

    What boat model, year, length?
    What is the make, model, material of current prop?
    What is the make, model and material of proposed prop.
    There are also considerations as to rake and cupping
    as well as 3 and 4 blades.
    aluminum to stainless.

    When I used the prop suggested by Propmann
    I gained hole shot and 3 mph on the top end
    as well as cornering speed.

    http://www.in-depthoutdoors.com/community/forums/topic/1675-impact-prop-selection/

    Jonesy
    Posts: 1148
    July 22, 2015 at 10:54 pm #1555984

    1. 1996 Alumacraft Dominator CS 16.5 feet
    2, BRP(Evinrude) 3 blade aluminum prop
    3. Same prop just in 15 pitch

    eyekatcher
    Lakeville, MN
    Posts: 966
    July 23, 2015 at 8:35 am #1556018

    That would probably be about +400 RPM
    (200 RPM per inch pitch)
    better hole shot
    not sure about top end

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