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peas

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  • Gavin Atkin
    Most of you will have seen this already. http://apci.net/~michalak/ If not, do check it out. In particular, if you ve heard me rambling about the seas of
    Message 1 of 3 , Apr 1, 2000
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      Most of you will have seen this already. http://apci.net/~michalak/

      If not, do check it out.

      In particular, if you've heard me rambling about the 'seas of peas' theory
      in the past, and wondered what on Earth I was gibbering about, this is an
      opportunity to find out more.

      And any ideas why these boats should be so fast? Could it be that the old
      speed/length rule just doesn't apply, and these boats plane or semi plane in
      a very smooth way that's actually not at all obvious when it happens?

      Cheers,

      Gav
    • Peter & Polly Vanderwaart
      This may be heresy..... I would like to see (or hear) the Bolger sharpie-shape theory discussed in its most complete form. Bolger is capable of both subtle
      Message 2 of 3 , Apr 3, 2000
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        This may be heresy.....

        I would like to see (or hear) the Bolger sharpie-shape theory
        discussed in its most complete form. Bolger is capable of both subtle
        thought and pedantic simplification, so I am reluctant take issue
        with him based on the short, simple explanations that he has put in
        articles.

        However...

        The proposition that the curve of the sides (i.e. angle of entry of
        the side) should match the curve of the bottom (i.e. angle of entry
        of the bottom) BECAUSE then the bottom pushes water down equally as
        the sides push water out seems to me to be flawed. Water under the
        boat is constrained because water can not be compressed. Water on the
        side of the boat can be forced upward. It seems to me that the Bolger
        Box form leads to higher pressure under the boat than on the sides.

        According to the Bolger Theory, this is desireable because it means
        water passes around the chine only in the bottom-to-side direction
        and not in the higher drag side-to-bottom direction.

        I do believe that he has proved on the water that the Bolger Box
        makes a superior boat in practice.

        Now, the question of why Bolger Boxes can be capable of high speeds.
        (Not that I believe in an 8kt Micro.) I think it is because of
        Bolger's oft repeated observation that a shallow boat can not make a
        deep wave. I will have to post my complete line of thought sometime,
        but the jist is this:

        The forward part of a boat depresses the water surface. As the boat
        goes by, water pressure pushes the surface back to the equilibrium
        level. (This pressure is set by the density of water, and is
        independant of boat length and speed.) If the water is not pushed up
        quickly enough to support the aft section of the boat, the stern
        falls, the boat gets out of trim and resistance increases. The boat
        has reached 'hull speed.' If the water is pushed up quickly, the boat
        stays in trim, resistance does not rise, and the boat can accelerate.

        It seems obvious that shorter the distance the water is displaced,
        the quicker it can rise to support the stern of the boat, and the
        faster the boat can go before it reaches hull speed. The Square Boats
        displace the surface about the smallest amount of any shape of boat,
        which may explain why they can generate unexpectedly high top speeds.

        Peter
      • Peter & Polly Vanderwaart
        This may be heresy..... I would like to see (or hear) the Bolger sharpie-shape theory discussed in its most complete form. Bolger is capable of both subtle
        Message 3 of 3 , Apr 3, 2000
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          This may be heresy.....

          I would like to see (or hear) the Bolger sharpie-shape theory
          discussed in its most complete form. Bolger is capable of both subtle
          thought and pedantic simplification, so I am reluctant take issue
          with him based on the short, simple explanations that he has put in
          articles.

          However...

          The proposition that the curve of the sides (i.e. angle of entry of
          the side) should match the curve of the bottom (i.e. angle of entry
          of the bottom) BECAUSE then the bottom pushes water down equally as
          the sides push water out seems to me to be flawed. Water under the
          boat is constrained because water can not be compressed. Water on the
          side of the boat can be forced upward. It seems to me that the Bolger
          Box form leads to higher pressure under the boat than on the sides.

          According to the Bolger Theory, this is desireable because it means
          water passes around the chine only in the bottom-to-side direction
          and not in the higher drag side-to-bottom direction.

          I do believe that he has proved on the water that the Bolger Box
          makes a superior boat in practice.

          Now, the question of why Bolger Boxes can be capable of high speeds.
          (Not that I believe in an 8kt Micro.) I think it is because of
          Bolger's oft repeated observation that a shallow boat can not make a
          deep wave. I will have to post my complete line of thought sometime,
          but the jist is this:

          The forward part of a boat depresses the water surface. As the boat
          goes by, water pressure pushes the surface back to the equilibrium
          level. (This pressure is set by the density of water, and is
          independant of boat length and speed.) If the water is not pushed up
          quickly enough to support the aft section of the boat, the stern
          falls, the boat gets out of trim and resistance increases. The boat
          has reached 'hull speed.' If the water is pushed up quickly, the boat
          stays in trim, resistance does not rise, and the boat can accelerate.

          It seems obvious that shorter the distance the water is displaced,
          the quicker it can rise to support the stern of the boat, and the
          faster the boat can go before it reaches hull speed. The Square Boats
          displace the surface about the smallest amount of any shape of boat,
          which may explain why they can generate unexpectedly high top speeds.

          Peter
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