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Twinkle Twinkle little boat

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  • rljssn
    I hope everyone had a great Christmas and happy new year. Quick question. On the Atkin s tunnel boat Twinkle. With the maximum recommended horse power of 9
    Message 1 of 10 , Jan 2, 2008
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      I hope everyone had a great Christmas and happy new year.

      Quick question. On the Atkin's tunnel boat Twinkle. With the maximum
      recommended horse power of 9 what would the top speed be? The Atkin's
      prose warns that she is not a speed boat. This power would be provided
      by an air cooled motor and rpm stepped down with pulleys (no reverse).

      I'm trying to get a wheel size from Michigan and they want this info.
      thanks for the help.
      Russ
    • Kenneth Grome
      Hi Russ, I would guess that this boat should not be driven any faster than 15-20 mph. One clue here is the last sentence in the description where Atkin says:
      Message 2 of 10 , Jan 2, 2008
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        Hi Russ,

        I would guess that this boat should not be driven any faster than 15-20
        mph. One clue here is the last sentence in the description where Atkin
        says:

        "Remember Twinkle is not a racing boat."

        The hull design with its straight run and flat bottom aft suggest that
        it is designed to be a planing boat, so it could probably be driven
        faster than this with a bigger engine.

        But if you use a 10 HP inboard and it won't push the boat faster than
        say 15 mph, higher theoretical speeds won't really matter anyways.

        Sincerely,
        Ken Grome
        Bagacay Boatworks
        www.bagacayboatworks.com





        > Quick question. On the Atkin's tunnel boat Twinkle. With the maximum
        > recommended horse power of 9 what would the top speed be? The Atkin's
        > prose warns that she is not a speed boat. This power would be
        > provided by an air cooled motor and rpm stepped down with pulleys (no
        > reverse).
        >
        > I'm trying to get a wheel size from Michigan and they want this info.
        > thanks for the help.
        > Russ
      • rljssn
        Ken, Do you really think Twinkle will go that fast with 9hp? She is carvel built 7/8 cedar sides and bottom on sawn oak frames(heavy). The article does read
        Message 3 of 10 , Jan 3, 2008
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          Ken,

          Do you really think Twinkle will go that fast with 9hp? She is carvel
          built 7/8" cedar sides and bottom on sawn oak frames(heavy). The
          article does read that with 3hp she should make 6 mph. I was planning
          a ply laptrake Ellon Jessup outboard skiff but decided to go with an
          inboard design after inspiration by the writings of the late Mr.
          White and his Rescue Minor skiff. This one has a simpler box tunnel
          than the RM. With a less efficient tunnel and alot smaller engine she
          should be a bit slower...but how much?

          I was also thinking around 14mph (just guessing). I can't judge these
          tunnel boats so well. Has anyone worked up the wheels for these
          Atkin's tunnel boats?
          thanks,
          Russell


          --- In AtkinBoats@yahoogroups.com, Kenneth Grome
          <bagacayboatworks@...> wrote:
          >
          > Hi Russ,
          >
          > I would guess that this boat should not be driven any faster than
          15-20
          > mph. One clue here is the last sentence in the description where
          Atkin
          > says:
          >
          > "Remember Twinkle is not a racing boat."
          >
          > The hull design with its straight run and flat bottom aft suggest
          that
          > it is designed to be a planing boat, so it could probably be driven
          > faster than this with a bigger engine.
          >
          > But if you use a 10 HP inboard and it won't push the boat faster
          than
          > say 15 mph, higher theoretical speeds won't really matter anyways.
          >
          > Sincerely,
          > Ken Grome
          > Bagacay Boatworks
          > www.bagacayboatworks.com
        • Kenneth Grome
          ... Maybe, but only if she can get out of the hole and onto plane with that 9 HP engine ... and I think this is the big question. I don t know what she will
          Message 4 of 10 , Jan 3, 2008
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            > Ken, do you really think Twinkle will go that
            > fast with 9hp?

            Maybe, but only if she can get "out of the hole" and onto plane with
            that 9 HP engine ... and I think this is the big question.

            I don't know what she will weigh when she's finished (do you?) ... but I
            do know she's a heavy boat compared with today's relatively lightweight
            boats, and it's going to take a lot of power to lift all that weight
            out of the hole and get the boat onto plane.

            Jim Michalak says it takes 1 HP per 50 pounds to get a boat to plane.
            This means the boat and contents should weigh less than 450 pounds if
            you're going to use a 9 HP engine to plane her. But won't this boat
            weigh more than 450 pounds with only one passenger? If so, I'm
            guessing it will not plane with 9 HP anyways, and if this is true you
            could probably get away with a much smaller engine ...


            > The article does read that with 3hp she should
            > make 6 mph.

            I suspect that this 6 mph figure is the boat's hull speed. A
            displacement hull wouldn't go much faster with additional or excess
            power, but this boat has a planing hull -- so additional power *might*
            move the boat faster in semi-displacement or semi-planing mode.

            Then again, maybe it would just run at 6 mph with a bow-high attitude
            and "remain in the hole" until enough more power were added to make it
            jump onto plane. I would hope that this is not the case, but if it is
            you may not be happy with the boat's performance if you try to push it
            faster than hull speed.

            You've selected a planing hull boat, are planing speeds important to
            you? How fast do you really want to go in this boat? Atkin has other
            inboard powered boats that may be better suited to displacement speeds.


            > I was planning a ply laptrake Ellon Jessup outboard
            > skiff but decided to go with an inboard design after
            > inspiration by the writings of the late Mr. White and
            > his Rescue Minor skiff.

            I think a lot of people are intrigued by Robb While's writings and
            boats. I've been designing a number of different tunnel-stern
            Seabright skiffs because of the inspiration I received from him as
            well ... and the Atkin's too of course.


            > This one has a simpler box tunnel than the RM. With
            > a less efficient tunnel and alot smaller engine she
            > should be a bit slower...but how much?

            Tunnel-stern Seabrights use a double-ended box keel which is basically a
            pirogue hull beneath an upper planing hull. The pirogue hull carries a
            substantial amount of the boat's weight and makes for a very easily
            driven hull with very low power requirements. I think this is the
            primary reason why the Atkin tunnel-stern Seabright skiffs move through
            the water more efficiently than most other hulls, especially in the
            range from displacement to low planing speeds.

            But Twinkle does not have the pirogue hull bottom to help with
            efficiency, so I don't think a direct comparison of these two hull
            types is appropriate here. It could very well be that Twinkle may not
            transition easily from displacement to planing speeds like the
            pirogue-bottom boats do.


            > Has anyone worked up the wheels for these
            > Atkin's tunnel boats?

            I don't think so.

            Sincerely,
            Ken Grome
            Bagacay Boatworks
            www.bagacayboatworks.com
          • 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 5 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 6 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 7 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 8 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 9 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 10 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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