Fish form revival: rough (very) draft.

Discussion in 'Boat Design' started by Alwaysthinking., Oct 25, 2019.

  1. Alwaysthinking.
    Joined: Sep 2019
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    Location: Colorado, USA

    Alwaysthinking. Junior Member

    I needed a break and got involved in other projects, so sorry I haven't posted anything about my stand-up paddle board/sit-on-top kayak design.
    Reminder: I had the theory that fish form had gotten a bad rap and just needed an update.
    Here is a rough draft I did several weeks ago. The bow is at the top. Bow is rockered. I should show a side profile.
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    The fish theory did not get a bad rap. It was shown that other forms are more efficient and/or faster. In science, when a theory is proven wrong it either discarded or use within the limits it is applicable. If you really think the fish shape is better, in whichever operation mode or limits you claim, then prove it by comparing the performance to a modern design. Drawings won't prove anything. Make some models and tow them side to side for a first comparison.
    Manfred.pech and fallguy like this.
  3. messabout
    Joined: Jan 2006
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    messabout Senior Member

    I agree with Gonzo. There may be isolated cases where the fishform is the better choice. Where much forward bearing is needed for example. The alternative, swedeform, layout is not necessarily the only other option.

    May I suggest that you give some consideration to the influence of shapes that affect the molecular accelerations of the water that you are pushing aside.
  4. rxcomposite
    Joined: Jan 2005
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    rxcomposite Senior Member

    It is not bad rep or anything. It is related to speed to length ratio or Froude number. Slow ships such as barge starts with box like shape, progresses to spoon bow or fish shape, then to full bodied ship with constant cross section, becomes finer and the shape reverses, and finally a reverse fish shape with very fine lines.

    The shape also relates to the Cb and its corresponding position of the LCB. Attached graph from Watson and Gilfillian lines.

    Attached Files:

  5. Eric ruttan
    Joined: Jul 2018
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    Location: usa

    Eric ruttan Senior Member

    This. With one caveat. The wrong theory is kept for history. We know the old idea was not as good as the new idea, because we have the record of how and why it was wrong.

    I think this is an important detail because one does not have to redo the work to reprove the weak points of the old theory.
    We do not edit out old theorys from history. We remember them.

    Thus, when someone brings up an idea, those who remember can point to all the data that made that idea weak, vs data that supports the idea or theory that replaced it.

    This process has an effect. When some approach those who have studied a field with a new idea, they are often told some version of 'been there, done that' by those who remember, or read, how we did that. And that dismissiveness can feel rather dismissive, because it is.

    Which is why no one thinks this old theory is any good.
    W9GFO likes this.

  6. rnlock
    Joined: Aug 2016
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    rnlock Senior Member

    I'm sure the fish form is reasonably good when fully submerged. Probably very efficient if tail flaps. ;-)
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