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Re: Twinkle Twinkle little boat

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  • sals_dad
    ... I put together a spreadsheet, using formulas from Gerr s Propeller Handbook, performance data from White s RM, and Noble Cab (similar to River Belle), and
    Message 1 of 10 , Jan 4, 2008
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      > > Has anyone worked up the wheels for these
      > > Atkin's tunnel boats?
      >
      > I don't think so.

      I put together a spreadsheet, using formulas from Gerr's Propeller
      Handbook, performance data from White's RM, and Noble Cab (similar to
      River Belle), and whatever I could glean from Atkin's writings.

      The spreadsheet is a bit rough, and is really useless without Gerr's
      book nearby. But I would be happy to share it.

      BTW - Gerr designed the power for Noble Cab, with (as I recall) 100HP
      Yanmar, 17x17 5 bladed prop (the prop cost more than any boat I have
      owned). I understand he expressed some scepticism as to whether it
      would perform as well as Atkins claimed. She met all expectations, and
      I suspect might have done better if Gerr had pushed her.
    • rljssn
      I don t have Gerr s book yet so I suppose the spreadsheet would not help me much. Thanks for the offer though. Part of the problem is that I m not sure what
      Message 2 of 10 , Jan 4, 2008
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        I don't have Gerr's book yet so I suppose the spreadsheet would not
        help me much. Thanks for the offer though.

        Part of the problem is that I'm not sure what engine was supposed to go
        in these boats originally. Typical small sizes (3hp) were often cast
        iron, two stroke, make-n-break ignition. Above twenty horsepower they
        were often small marine four cylinder equipped from Grey marine or
        Redwing, etc. What were the in between marine motors like? A ten horse
        make-n-break is heavy. That could weigh as much as the hull! I would
        suppose the hull to be around 300-400lbs. This makes estimating the
        weight to horsepower difficult.

        I would think the tunnel would force the bow down in acceleration like
        on Mr. Whites RM. The jet of water from the tunnel would pull the water
        from transom and make it difficult to tell when she would be on plane.
        This design is right at the threshhold of a semi-planing boat. The
        concern is that she might not perform well unless very lightly loaded.
        If fuel mileage in this day were not a concern I would build a Little
        Water. :)
      • Ronald Fossum
        Well, since we re talking a planing (or semi-planing) boat and somewhere in the same time period as RM, the 15HP RM engine was pegged by Bill A at about 340# &
        Message 3 of 10 , Jan 4, 2008
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          Well, since we're talking a planing (or semi-planing) boat and somewhere in the same time period as RM, the 15HP RM engine was pegged by Bill A at about 340# & 91ci. As to the smaller engines, I remember in the late 40s that 16' inboards in the Puget Sound (rental boats at "resorts") usually had a 2 or 3HP Briggs & Stratton or equivalent (Reinell and Marysville Boat Works both used that) and they moved along quite nicely at 6 or so knots (nobody really measured that sort of thing back then - it just got you there fast enough or it didn't).


          ----- Original Message -----
          From: rljssn
          To: AtkinBoats@yahoogroups.com
          Sent: Friday, January 04, 2008 3:46 PM
          Subject: [AtkinBoats] Re: Twinkle Twinkle little boat


          I don't have Gerr's book yet so I suppose the spreadsheet would not
          help me much. Thanks for the offer though.

          Part of the problem is that I'm not sure what engine was supposed to go
          in these boats originally. Typical small sizes (3hp) were often cast
          iron, two stroke, make-n-break ignition. Above twenty horsepower they
          were often small marine four cylinder equipped from Grey marine or
          Redwing, etc. What were the in between marine motors like? A ten horse
          make-n-break is heavy. That could weigh as much as the hull! I would
          suppose the hull to be around 300-400lbs. This makes estimating the
          weight to horsepower difficult.

          I would think the tunnel would force the bow down in acceleration like
          on Mr. Whites RM. The jet of water from the tunnel would pull the water
          from transom and make it difficult to tell when she would be on plane.
          This design is right at the threshhold of a semi-planing boat. The
          concern is that she might not perform well unless very lightly loaded.
          If fuel mileage in this day were not a concern I would build a Little
          Water. :)





          [Non-text portions of this message have been removed]
        • rljssn
          i tried one of those prop calculators on the net. 9hp engine running at 3600rpm reduced 2:1 at the prop. The boat displaces 1000lb total (hull, motor, people).
          Message 4 of 10 , Jan 4, 2008
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            i tried one of those prop calculators on the net.
            9hp engine running at 3600rpm reduced 2:1 at the prop.
            The boat displaces 1000lb total (hull, motor, people).
            15.5' waterline length brings a 5.2mph displacement speed.

            All of this yields a propeller of 11 inch diameter and 18 inches of
            pitch to get the hull to 16 mph.

            I think I'm getting close because the Atkin drawing looks like a 10"
            diameter propeller with a little clearance.

            Russell
          • Kenneth Grome
            ... Maybe, but I wouldn t bet on it having as much downward thrust as the Atkin tunnel-stern boats. The tunnel-sterns use the entire width of the boat to
            Message 5 of 10 , Jan 4, 2008
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              > I would think the tunnel would force the bow
              > down in acceleration like on Mr. Whites RM.

              Maybe, but I wouldn't bet on it having as much downward thrust as the
              Atkin tunnel-stern boats.

              The tunnel-sterns use the entire width of the boat to direct the water
              downward. By directing so much more water downward, they can use far
              less hook in the aft hull bottom than I see in Twinkle's tunnel
              section ... and I think the less hook used to direct water downward,
              the more fuel efficient the boat will be.

              Do you need a tunnel hull for propeller clearance where you're planning
              to use the boat?

              Sincerely,
              Ken Grome
              Bagacay Boatworks
              www.bagacayboatworks.com
            • rljssn
              The tunnel boat is for the super shallow water we have here. We are in drought level four here in Georgia and the water levels are so low most boats are seeing
              Message 6 of 10 , Jan 6, 2008
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                The tunnel boat is for the super shallow water we have here. We are in
                drought level four here in Georgia and the water levels are so low most
                boats are seeing very little use because of the danger to exposed
                stumps. This large man made lake is notorious for eating props (even at
                high water levels). The shallow draft on Twinkle along with the
                efficient four stroke engine might work very nice in these conditions.
                I'm not tournament bass fishing so I don't need alot of speed.

                I understand about the Rescue Minor's tunnel. In the article on Twinkle
                it is mentioned. I have studied all the tunnel boats but like this one
                for the simplicity and size.

                I'm waiting for Michigan Wheel to get back to me on the prop size.
                I'll let everyone know what they recommend.

                thanks,
                Russ
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