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Re:Gear reduction for Little Effort

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  • JJ Johnson
    Not to disagree with Kenneth, but I would come at the problem from a different direction. Measure the distance from your shaft to the hull, double it and take
    Message 1 of 8 , Dec 20, 2006
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      Not to disagree with Kenneth, but I would come at the problem from a different direction.
      Measure the distance from your shaft to the hull, double it and take 80% for Maximum Prop diameter. Now go to your prop supplier, tell him how the boat will be used and follow his suggestion for reduction gearing. Personally for displacement speeds I like a prop to turn a max of 1250 rpm. If you want to get above the displacement speed range, your prop rpm can be much higher and the max diameter can be smaller. But pay attention to your prop supplier, he will know much better than I what will work for your boat.
      If you would like to play what if games with a spreadsheet, PropKIngX is a free download that will get you into the ball park for diameter, pitch, and rpm by varing the boat speed, engine rpm, reduction, power available, etc... It is very easy to use and I think it is in the files section. If not in this group then one of the other Yahoo groups on boat building.
      If you don't find it, send me a message and I'll send it to you direct. If you don't have a spreadsheet, OpenOffice is available as a free download for Windows and Linux systems.



      Regards
      JJ & Irene
      Rockport Tx.
      78382


      Science without religion is lame,
      religion without science is blind.



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    • Rob Rohde-Szudy
      Nowhere is this all better explained than in The Propeller Handbook by Dave Gerr. I think Duckworks carries it. --Rob Gear reduction for Little Effort Posted
      Message 2 of 8 , Dec 20, 2006
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        Nowhere is this all better explained than in The Propeller Handbook by Dave Gerr. I think Duckworks carries it.
        --Rob


        Gear reduction for Little Effort
        Posted by: "adharvey2" adharvey@... adharvey2
        Date: Tue Dec 19, 2006 7:32 pm ((PST))

        I'm open to suggestions regarding grear reduction using the Kubota
        engine in Little Effort. I'm a complete neophyte when it comes to
        inboards. The designed engine ran at 2000 rpm with no reduction, but
        I'm told by my marine diesel mechanic friend in Seattle that 2000
        shaft rpm is not the norm these days, but he's used to engines larger
        than my car (they do work on engines of this size and type but only as
        gensets). I'd like to hear from an experienced inboard
        utility/runabout person about optimal shaft rpm and prop specs in
        this aplication. I'm sure prop technology has advanced some in 50
        years. The kubota has an incredibly flat torque curve so it could be
        happy at 1800 or 2800 rpm or whatever.
        He picked up the motor (mechanic friend) which I bought on ebay
        for $381, and it looks like it may just need bearings. It had been run
        out of oil and started to make some wrong noises, so they replaced it
        with a new one ($6400).
        Still awaiting the study plans and looking forward to some more
        info soon.
        Andrew


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      • sals_dad
        ... Handbook by Dave Gerr. I think Duckworks carries it. ... I ll second Rob s recommendation. Atkin s drive systems were something special - even bizarre,
        Message 3 of 8 , Dec 21, 2006
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          > Nowhere is this all better explained than in The Propeller
          Handbook by Dave Gerr. I think Duckworks carries it.
          > --Rob
          >

          I'll second Rob's recommendation. Atkin's drive systems were
          something special - even bizarre, by today's standards. For "Noble
          Cab", Dave Gerr re-designed the drive train, and ended up specing a
          17x17 5 bladed prop, with something like 95% coverage ratio (wrong
          terminology, I know). That prop had to be custom fabricated in
          Australia - and cost more than any boat I have ever owned.

          For Rescue Minor, I consulted with several prop specialists. The
          unanimous response was "impossible", "will never work".

          After a long time with Gerr's book and a spreadsheet, I came up with
          solutions very similar to Robb White's. I have the spreadsheet
          somewhere, kinda rough, and no documentation, but it might save
          somebody a few hours working out Gerr's formulas

          Sal's Dad.
        • John Kohnen
          Bizarre? Most of Wm. and John Atkin s motorboats use direct drive, no reduction, for simplicity and lower cost, I d guess, and the low to medium speed engines
          Message 4 of 8 , Dec 22, 2006
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            Bizarre? Most of Wm. and John Atkin's motorboats use direct drive, no
            reduction, for simplicity and lower cost, I'd guess, and the low to medium
            speed engines available in William's day could turn a decent sized prop
            direct at a suitable speed without complaining. Nothing bizarre about any
            of that. <shrug> Nowadays even light diesels turn faster than many of the
            gas engines William favored, so a reduction gear might need be used. In
            some cases, if you're going to pungle up the dough for a reduction gear
            anyway, it might make sense to gear down enough to use a larger propeller.
            Generally though, if you can get a reduction gear that'll turn the prop
            shaft at about the speed the Atkin's intended that's a good start. Then
            consult Gerr's Propeller Handbook.

            On Thu, 21 Dec 2006 07:35:44 -0800, Sal's Dad wrote:

            >> Nowhere is this all better explained than in The Propeller
            > Handbook by Dave Gerr. I think Duckworks carries it.
            >> --Rob
            >>
            >
            > I'll second Rob's recommendation. Atkin's drive systems were
            > something special - even bizarre, by today's standards.
            > ...

            --
            John <jkohnen@...>
            Power always has to be kept in check; power exercised in secret,
            especially under the cloak of national security, is doubly
            dangerous. <William Proxmire>
          • John Kohnen
            For displacement hulls like those huge engines usually push a big, slow propeller is most efficient. But Little Effort is intended for planing speeds, so a
            Message 5 of 8 , Dec 22, 2006
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              For displacement hulls like those huge engines usually push a big, slow
              propeller is most efficient. But Little Effort is intended for planing
              speeds, so a smaller, faster propeller will work best. The propeller
              called for in the plans is 11" dia. by 12" pitch. If you can find, or
              make, a reduction gear that'll turn the shaft around 2,000 rpm that should
              be fine, but if you run a direct drive from the engine and prop it so the
              engine turns 2,000 rpm you won't get anywhere near the advertised 33 hp.

              If you can find a direct drive reverse gear you could use a cogged belt to
              the prop shaft. That'd make it easy to get just the amount of reduction
              you want.

              On Tue, 19 Dec 2006 19:27:20 -0800, Andrew wrote:

              > ...
              > I'm a complete neophyte when it comes to
              > inboards. The designed engine ran at 2000 rpm with no reduction, but
              > I'm told by my marine diesel mechanic friend in Seattle that 2000
              > shaft rpm is not the norm these days, but he's used to engines larger
              > than my car
              > ...
              > I'm sure prop technology has advanced some in 50
              > years. The kubota has an incredibly flat torque curve so it could be
              > happy at 1800 or 2800 rpm or whatever.
              > ...

              --
              John <jkohnen@...>
              Distrust any enterprise that requires new clothes. <Henry David
              Thoreau>
            • Ronald Fossum
              Thank you John for this and the previous posting. I m still moving ahead on a steam powered version of Rescue Minor and find that Bill s propeller selection
              Message 6 of 8 , Dec 22, 2006
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                Thank you John for this and the previous posting. I'm still moving ahead on
                a steam powered version of Rescue Minor and find that Bill's propeller
                selection (based on prop tables and formulas - including Dave Gerr's) is
                exactly right. My difference is the steam power part of the equation. Rob
                White's use of a different propeller (not very different really) was based
                on engine rpm (about 800 rpm faster) and the resultant hp at that rpm. But
                working forward to that from Bill's propeller, it comes in about right. I've
                had experience with "angled off center" props and I must say that, done
                correctly, they do make for improved handling. A radical example of what
                happens with an inline shaft and high horsepower and be observed when such a
                boat "guns the engine" when underway.

                Merry Christmas all.

                Ron Fossum
                ----- Original Message -----
                From: "John Kohnen" <jkohnen@...>
                To: <AtkinBoats@yahoogroups.com>
                Sent: Friday, December 22, 2006 12:47 AM
                Subject: Re: [AtkinBoats] Gear reduction for Little Effort


                > For displacement hulls like those huge engines usually push a big, slow
                > propeller is most efficient. But Little Effort is intended for planing
                > speeds, so a smaller, faster propeller will work best. The propeller
                > called for in the plans is 11" dia. by 12" pitch. If you can find, or
                > make, a reduction gear that'll turn the shaft around 2,000 rpm that should
                > be fine, but if you run a direct drive from the engine and prop it so the
                > engine turns 2,000 rpm you won't get anywhere near the advertised 33 hp.
                >
                > If you can find a direct drive reverse gear you could use a cogged belt to
                > the prop shaft. That'd make it easy to get just the amount of reduction
                > you want.
                >
                > On Tue, 19 Dec 2006 19:27:20 -0800, Andrew wrote:
                >
                >> ...
                >> I'm a complete neophyte when it comes to
                >> inboards. The designed engine ran at 2000 rpm with no reduction, but
                >> I'm told by my marine diesel mechanic friend in Seattle that 2000
                >> shaft rpm is not the norm these days, but he's used to engines larger
                >> than my car
                >> ...
                >> I'm sure prop technology has advanced some in 50
                >> years. The kubota has an incredibly flat torque curve so it could be
                >> happy at 1800 or 2800 rpm or whatever.
                >> ...
                >
                > --
                > John <jkohnen@...>
                > Distrust any enterprise that requires new clothes. <Henry David
                > Thoreau>
                >
                >
                > No flaming, cursing, politics, religion or public mopery. Please be
                > polite.
                >
                > If you set out to build an Atkin boat, please do not modify the plans. If
                > you stray from the plans you do so at your own risk and Atkin & Co. will
                > take no responsibility for the performance of the resulting boat.
                >
                > The current Atkin boat plans catalog is online at
                > <http://www.atkinboatplans.com/>
                >
                >
                > Yahoo! Groups Links
                >
                >
                >
                >
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