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Re: [AtkinBoats] Gear reduction for Little Effort

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  • 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 1 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 2 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/>
        >
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