Scaling Down a Sharpie

Discussion in 'Boat Design' started by FromMystic, Mar 14, 2017.

  1. PAR
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    PAR Yacht Designer/Builder

    Surely TANSL, you're aware of the issues that arise with mechanical similitude and particularly the dynamic relationships that occur on a reduction of this scale?Hydrodynamically it will be very difficult, structurally, all but impossible, if a true a proportionate scaling is performed. Langley discovered this in reverse quite dramatically when his Aërodrome, broke up, just after leaving the catapult and the bits plunged into the Potomac. He'd scaled up the model, structure and all and any reasonable engineer would know, not to do this, even in his day.
     
  2. TANSL
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    TANSL Senior Member

    There is no doubt that I am expressing myself wrong. When I say that the lines can be scaled I do not say that the structure can be scaled. I'm just saying, let's see if you understand me, that the lines can be escalated. This will give a hull from which the structure will have to be recalculated (Not Scaled), in its layout and in the thicknesses of its panels, module of the reinforcement, etc. As a consequence, the weight of the hull must be recalculated (Not Scaled). As a consequence many things will change, for example, the draft of the ship at full load will Not be the same. The maximum number of people on board will be different, Not The Scale of the previous one. The size of the anchor will be different than the one obtained by scaling the previous one. The weight of the skipper could be the same. And so on ......
    In short, the lines will be able to be scaled (without any limitation) but Absolutely nothing more. Everything else will change differently than the applied scale. If I do not explain myself right now, I'm sorry, I can not do better. Excuse me for my awkwardness and forgive me for the time I have made you lose with me.
    Greetings to all.

    P.S. Sorry PAR, I'm not aware of the issues that arise with mechanical similitude and particularly the dynamic relationships that occur on a reduction of this scale. Any explanation, please?
     
    Last edited: Mar 18, 2017
  3. Angélique
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    Angélique aka Angel (only by name)

  4. TANSL
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    TANSL Senior Member

    Angélique, is it all right if we answer what FromMystic asked? :
    My answer: you can scale the lines without problem but, as you already intuit, you have to take into account that, among many other things, you will have to recalculate the draft and, probably, the freeboard. Therefore, the total depth will probably not maintain the scale of the other dimensions.
     
  5. gonzo
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    gonzo Senior Member

    You can scale the lines. For example, model ships are scaled down versions. However, scaling lines by a large percentage do not generate a design that can be successful.
     
  6. TANSL
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    TANSL Senior Member

    A design consists of many parts, one of which is the hull lines. It is clear that modifying one of the important parts of a project will lead us to have to modify some other parts. I mean that modifying only one of the important parts of a project, without more, can not normally lead to a valid project.
     
  7. Angélique
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    Angélique aka Angel (only by name)

    The bunch of links in post #33 is an on topic reply to the misperceptions in your post #32, hence it's responding to the post directly above it as often is the case with forum replies when not is indicated otherwise, and I'm not going to spell it out for you, it's just intended for self read for anyone interested.

    BTW, thanks for your post #17 [​IMG] - I very much agree to it :)
     
  8. TANSL
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    TANSL Senior Member

    Thanks Angélique, really. It is probably very valuable information, which I will not read. I would prefer a one or two line answer for such a simple thing. If I had needed to search the internet or specialized forums, I would have done so, I feel empowered to do so. Thank you.
     
    Last edited: Mar 20, 2017
  9. PAR
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    PAR Yacht Designer/Builder

    Yes, you can scale the lines, but the results can't be used in this form. In the case of this particular reduction, it's plainly clear the hull's volume will need to change considerably, just to hold up the crew, let alone its rig, so though the lines can be scaled, but to what end other than an academic exercise in scaling lines.
     
  10. TANSL
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    TANSL Senior Member

    I agree with the first part of your post, since it is what I have been saying for several days.
    Regarding the question you ask, there are many possible answers but I will only raise one: have you ever seen the scale models that are made of cars, planes, ships, trains, ....? They are not at all academic exercises, they are realities.
     
  11. gonzo
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    gonzo Senior Member

    The behavior of models is very different from that of the full scale object. There is a branch of engineering that deals with the difference. It tries, with limited success, to extrapolate the result of model testing to apply it to full size things.
     
  12. TANSL
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    TANSL Senior Member

    Good comment, Gonzo. I would like to know what that special branch of the engineering is to go deeper into it. Must be an exciting branch.
    Limited succes :confused:. I had always believed that testings with models, with correct correlation coefficients, were a complete success.:(
     
  13. gonzo
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    gonzo Senior Member

    It is called model testing. If the tests were a complete success, there would be no need to do beta testing at full scale to correct errors and unpredictable behavior.
     
  14. TANSL
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    TANSL Senior Member


  15. Ilan Voyager
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    Ilan Voyager Senior Member

    The most beautiful failure I know was the 12 M JI Mariner designed by Britton Chance Jr. The boat was nicknamed the "Pregnant Whale"
    I say beautiful because that was an excess of trust on "science", but nobody died or was hurt, except some prides and wallets.
    Curiously the wiki bio of Chance does not say a word and I found only a pic in Pinterest. And none info.

    The model tank tests gave fabulous results with the sharp cut bustle and the forward round underwater entries in conjunction with a formidable belly. I do remember the triumphant communicates. On the water the 1/1 model (joke) was a dog, a bad one, dragging more water than a barge...and a successful 12 M JI drags already a lot of water. The 12M JI rule had some perversities. What year? After Intrepid in 1970. Internet seems to be silent on the subject.
     

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