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Re: [AtkinBoats] Re: flat bottom design

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  • Michael Bogoger
    It s a question of efficiency. If you look at the watermark left on a flat bottom boat when it s pulled from the water you will see that those with more
    Message 1 of 9 , Mar 4 9:58 AM
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      It's a question of efficiency. If you look at the watermark left on a "flat bottom"  boat when it's pulled from the water you will see that those with more "rocker" have very little contact with the water as it leaves the stern of the boat and will offer very little resistance and leave almost no wake. The more surface area in contact with the water at the stern, the more resistance and more horsepower will be required to move the boat, at slow speeds but more remarkably at higher speeds. As Gavin says, a boat with rocker will not plane like a flatter run aft, but will reach speeds up to 20 knots with more efficiency, thus a smaller motor. A slight "V" in the hull aft is even better.

      doryman



      On Fri, Mar 4, 2011 at 5:49 AM, gavin atkin <gavinatkin@...> wrote:


      Glad to help.

      There's a tricky third way called semi-planing, which is what many sailing do. In this case the transom is either on the water or only a little way below. The idea here is that once a good speed is achieved the water swooshes back to the surface a little way aft of the boat, which makes the water behave as if the boat were an little longer - and therefore due to a change in the physics of  wavemaking, a little faster. Some low power outboard boats get a bit more speed this way.

      Gav    


      --- On Fri, 4/3/11, Billy <billybronaugh@...> wrote:

      From: Billy <billybronaugh@...>
      Subject: [AtkinBoats] Re: flat bottom design
      To: AtkinBoats@yahoogroups.com
      Date: Friday, 4 March, 2011, 13:29


       

      Thanks Gavin,I didn't think of that aspect, I was wondering mainly about trim and load carrying capacity and load (operator) placement. So, in that respect they share that design trait with rowing boats. I keep wanting to build Elon Jessup, Punch has caught my eye recently too, and was wondering why the tuck up in thier hulls. Punch seems to have less but both transoms clear the water.

      - In AtkinBoats@yahoogroups.com, gavin atkin <gavinatkin@...> wrote:
      >
      > With a small outboard there's no chance of planing, and a straight run would mean the transom dragging in the water.
      >
      > So these boats are often more like rowing boats, than they are like modern planing craft.
      >
      > Gavin (no relation that I know of)
      >
      > --- On Fri, 4/3/11, Billy <billybronaugh@...> wrote:
      >
      > From: Billy <billybronaugh@...>
      > Subject: [AtkinBoats] Re: flat bottom design
      > To: AtkinBoats@yahoogroups.com
      > Date: Friday, 4 March, 2011, 3:13
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      > I didn't see an adit option so......I guess what I am asking, not meaning to single out William and John, is what is the purpose of rocker aft on an outboard boat?
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      > --- In AtkinBoats@yahoogroups.com, "Billy" <billybronaugh@> wrote:
      >
      > >
      >
      > > OK, so why did William and John design the bottoms of their flat bottom skiffs designed for outboards with the seemingly generous amount of rocker, especially aft where, at least with an outboard, it seems contrary to more modern design practice.
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      >





    • John Kohnen
      At moderate speeds the rockered bottom will be more efficient. When out alone in an Atkin skiff you do have to use a tiller extension and get your weight out
      Message 2 of 9 , Mar 6 3:05 PM
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        At moderate speeds the rockered bottom will be more efficient. When out
        alone in an Atkin skiff you do have to use a tiller extension and get your
        weight out of the stern. A good bit of the reason for the fat, flat a** of
        more modern outboards isn't just high speed planing, it's to support the
        fat a** of someone running a big motor while sitting right next to it. <g>
        The more shapely Atkin skiffs will be more seaworthy than a fat a**ed
        modern skiff too, since the buoyancy and weights are closer to the middle
        of the boat.

        On Thu, 03 Mar 2011 18:42:48 -0800, Billy wrote:

        > OK, so why did William and John design the bottoms of their flat bottom
        > skiffs designed for outboards with the seemingly generous amount of
        > rocker, especially aft where, at least with an outboard, it seems
        > contrary to more modern design practice.

        --
        John (jkohnen@...)
        Let us enrich ourselves with our mutual differences. (Paul Valery)
      • Billy
        Instead of using a tiller ext could one use ropes around the perimeter of the boat for :anywhere: steering like with a tiller?
        Message 3 of 9 , Mar 11 4:31 PM
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          Instead of using a tiller ext could one use ropes around the perimeter of the boat for :anywhere: steering like with a tiller?
          --- In AtkinBoats@yahoogroups.com, "John Kohnen" <jkohnen@...> wrote:
          >
          > At moderate speeds the rockered bottom will be more efficient. When out
          > alone in an Atkin skiff you do have to use a tiller extension and get your
          > weight out of the stern. A good bit of the reason for the fat, flat a** of
          > more modern outboards isn't just high speed planing, it's to support the
          > fat a** of someone running a big motor while sitting right next to it. <g>
          > The more shapely Atkin skiffs will be more seaworthy than a fat a**ed
          > modern skiff too, since the buoyancy and weights are closer to the middle
          > of the boat.
          >
          > On Thu, 03 Mar 2011 18:42:48 -0800, Billy wrote:
          >
          > > OK, so why did William and John design the bottoms of their flat bottom
          > > skiffs designed for outboards with the seemingly generous amount of
          > > rocker, especially aft where, at least with an outboard, it seems
          > > contrary to more modern design practice.
          >
          > --
          > John (jkohnen@...)
          > Let us enrich ourselves with our mutual differences. (Paul Valery)
          >
        • John Kohnen
          Certainly: http://www.boat-links.com/Atkinco/Photos/Scandal/ ... -- John (jkohnen@boat-links.com) The most persistent threat to freedom, to the rights of
          Message 4 of 9 , Mar 11 4:35 PM
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            Certainly:

            http://www.boat-links.com/Atkinco/Photos/Scandal/

            On Fri, 11 Mar 2011 16:31:53 -0800, Billy wrote:

            >
            > Instead of using a tiller ext could one use ropes around the perimeter

            --
            John (jkohnen@...)
            The most persistent threat to freedom, to the rights of
            Americans, is fear. (George Meany)
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