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How Important is the Gearbox Ratio?

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  • How Important is the Gearbox Ratio?

    Hello all from Brisbane, Australia.

    I am in the market for a new outboard to replace my 1999 Johnson 35Hp 3-cyl 2-stroke on my 3.9m aluminium hull (side console Quintrex Hornet Trophy). The hull is rated to 40Hp with a max allowed motor weight of 118kg.

    The candidates are the PTT 40Hp 4-strokes from Yamaha, Honda, Suzuki and Tohatsu. I can’t quite shake the idea of a 30Hp E-tec either.

    Top speed is not a priority for me but getting onto the plane quickly is. My boat is not big, but could be at the heavier end of the scale with live well, keeper tank, duel batteries, 24L fuel, electric bow mount, ice box, tackle, fishing buddy etc.

    One of the differences, in the glossy brochures, is the gearbox ratio of these engines. Yamaha is the tallest at 2.0:1. Honda and Tohatsu are 2.08:1; Suzuki is 2.42:1; the E-tec is 2.15:1.

    Should the gearbox ratio play a part in my decision on which outboard to buy?

    Or would the propeller pitch have a greater influence on “hole shot” performance anyway?

    Good advice appreciated.

  • #2
    The 35 HP 3 cylinder Johnson is a solid motor.----Why not maintain / keep it ??

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    • #3
      The different gear ratios mean that prop pitches selected for these motors differs.-----The Yamaha would use say a 14" pitch.-----The Suzuki would use a 16" pitch.

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      • #4
        A gear box simply multiples the torque while lowering the rpm output of a motor. Simply torque x rpm = Hp

        The fact that all the motors under consideration are rated the same tells you the output of each motor is slightly different.

        The wrench in this is that regulation allow a 10% variation from the advertised HP. The actual output of a 40 hp rated motor can vary plus or minus 4 HP. Pretty significant difference.

        To get a real picture of what is going on you need to compare HP and torque curves for each engine.

        Having said that, select the motor that has the best support in your area. Makes no sense to drive an hour to get support for brand A when the brand B shop is across the street
        ....

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        • #5
          Doesn't matter much the gear ratio the motor manufacturer has put inside the lower unit, can play with prop pitches all you want to make the motor to run at least middle to max wot rpm range factory stated as loaded.

          Happy Boating


          Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers

          Comment


          • #6
            Originally posted by racerone View Post
            The 35 HP 3 cylinder Johnson is a solid motor.----Why not maintain / keep it ??
            I do like the motor and it is running well at the moment. I just like the idea of what the modern engines offer (trolling idle speed adjustment, NMEA2000 compatability etc).

            The only local Dealer who can truly support these older Johnson/Evinrude outboards has retired. USA based genuine spare parts Suppliers won't sell to me in Australia unfortunately.

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            • #7
              Call a dealer.----Set up an account.----I know one dealer that has a website and I am positive he would ship you the parts !!

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              • #8
                Originally posted by racerone View Post
                The 35 HP 3 cylinder Johnson is a solid motor.----Why not maintain / keep it ??
                3 cylinders on that small of an engine I'll bet runs smooth as silk. That's one thing I liked about the classic Mercs and the Towers. Lots of cylinders/cu in of displacement meant smoooooooth running, especially when compared to the '50-'60's coughing, sneezing, I'll start when I feel like it OMC twins.
                If you are new to boating or have a new boat, a knowledgeable friend could show you how to operate your boat and save you a lot of grief, maybe some money, and maybe your life.

                Comment


                • #9
                  Originally posted by Texasmark View Post

                  3 cylinders on that small of an engine I'll bet runs smooth as silk. That's one thing I liked about the classic Mercs and the Towers. Lots of cylinders/cu in of displacement meant smoooooooth running, especially when compared to the '50-'60's coughing, sneezing, I'll start when I feel like it OMC twins.
                  I.want some.of what you are smoking.

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                  • #10
                    Agreed ----Worked on many OMC twins.-----Was on water skis behind them too.-----Nothing wrong with them and many are still running today.

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                    • #11
                      Searider is right. All about the propping of the set up.

                      if you want to shift a heavy boat with lower than normal HP though, there isn’t much better than the new mercury command thrust units. Not sure they go as low as this though. Not far off it though.

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                      • #12
                        Originally posted by flyingscott View Post

                        I.want some.of what you are smoking.
                        Yet another useful and meaningful input to the discussion. Perhaps your request above helps explain a lot previously FS. Haha.
                        please forgive me. Couldn’t resist it, my friend ! All in jest !

                        Comment


                        • #13
                          Originally posted by QBhoy View Post

                          Yet another useful and meaningful input to the discussion. Perhaps your request above helps explain a lot previously FS. Haha.
                          please forgive me. Couldn’t resist it, my friend ! All in jest !
                          Of course I forgive you. I understand you are still in pain from finding out your prop is obsolete. If you were closer I would offer you a hug my friend.

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                          • #14
                            Originally posted by flyingscott View Post

                            Of course I forgive you. I understand you are still in pain from finding out your prop is obsolete. If you were closer I would offer you a hug my friend.
                            Oh shucks...

                            Comment


                            • #15
                              Sign up today
                              Originally posted by QBhoy View Post

                              Yet another useful and meaningful input to the discussion. Perhaps your request above helps explain a lot previously FS. Haha.
                              please forgive me. Couldn’t resist it, my friend ! All in jest !
                              I had my fill of alternate firing twins growing up and Johnnyrudes were all around me, like other brands with their manual low and high speed carb. adjustments. My first experience with a multi cylinder engine was a new 1957-9 (somewhere in there) Wizard 25 (Merc Mark 30 derivative) I purchased for $400 from a local Western Auto store.....brochures of the day are on the www. Sweet running, smooth power.

                              No doubt a 25 horse Johnnyrude could plane out a 16' wooden, wide beam, bay boat (shorter version of this: https://www.ladyben.com/power-classi...s/view-details ) with a couple of guys, couple of 6 gallon tanks of gas and their gear just fine, but at low speeds/idling, like picking up a skier (on 2 skis, not too heavy), while starting or in the no-wake zone, ugh.

                              What does this add to the posting? A reason to look at newer engines with a lot of those older problems solved. Different folks have different feelings..........on smoking, I quit in 1988 when I bought a new F150 with velour upholstery and didn't want to stink it up. Don't drink.
                              If you are new to boating or have a new boat, a knowledgeable friend could show you how to operate your boat and save you a lot of grief, maybe some money, and maybe your life.

                              Comment

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