Loading ...
Sorry, an error occurred while loading the content.

Re: [AtkinBoats] Twinkle Twinkle little boat

Expand Messages
  • 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 1 of 10 , Jan 2, 2008
    • 0 Attachment
      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 2 of 10 , Jan 3, 2008
      • 0 Attachment
        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 3 of 10 , Jan 3, 2008
        • 0 Attachment
          > 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 4 of 10 , Jan 4, 2008
          • 0 Attachment
            > > 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 5 of 10 , Jan 4, 2008
            • 0 Attachment
              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 6 of 10 , Jan 4, 2008
              • 0 Attachment
                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 7 of 10 , Jan 4, 2008
                • 0 Attachment
                  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 8 of 10 , Jan 4, 2008
                  • 0 Attachment
                    > 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 9 of 10 , Jan 6, 2008
                    • 0 Attachment
                      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
                    Your message has been successfully submitted and would be delivered to recipients shortly.