1/4 scale model

Discussion in 'Sailboats' started by Howlandwoodworks, Jun 11, 2019.

  1. Earl Boebert
    Joined: Dec 2005
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    Location: Albuquerque NM USA

    Earl Boebert Senior Member

    Yes. It's like the "stand off scale" idea in model airplanes. From twenty feet away your model looks like a P-38. Up close a P-38 expert can find a hundred things wrong with it: bigger elevator, wings forward, whatever you did to make it fly well.

    The average scale sailboat builder just wants to make a model that looks right and sails well. That's what John Black did with Yankee Jr. If you want to use the model to learn something about a proposed full-size boat, you're in a different problem domain.


  2. Howlandwoodworks
    Joined: Sep 2018
    Posts: 145
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    Location: MO

    Howlandwoodworks Member

    I checked the center of buoyancy CB yesterday in a tank of water. It was on the water line.
    I though about putting a Dragon type keel on but if I build and can't sell it I will be sailing on inland lakes. The keels overall depth is a little deeper than an outboard motor. And finding boat ramps that will accommodate a deep keel are hard to find around here.
    I am going to fasten the keel and put some kind of transparent finish on the hull after grind off a bone headed idea I had. I add on to the keel making it proud from the hull, a division in between starboard and port, like a power boat. Well it's only a 1/4 scale mistake.
  3. Howlandwoodworks
    Joined: Sep 2018
    Posts: 145
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    Location: MO

    Howlandwoodworks Member

    My first line above should have read.
    I checked the center of buoyancy with water yesterday, filed the hull with water to the water line and then took half out. Then with a dry bilge I set the 1/4 scale model in a tank of water, it sat on its waterline.
    I know that the VBC will take the Simpson's rule. I have the Table of Offsets in 8" sections in Excel now and have started to divide them into 2" sections of the below the waterline area for the Simpson's rule. After I have the COB I can start on the Dellenbaugh angle.
    I have acquired some of the easer numbers for my little boat such as the SA/D, D/LWL, BN, Sw, Aw, Ax, etc... There are a couple of pages of other numbers that I haven't acquired yet. After I calculator the more important numbers I will redesign the Wetted surface, keels root and tip of my little sailboat.
    Is this a viral or a mental issue that I have acquired about boats?
    Last edited: Sep 6, 2019
    Dolfiman and Doug Lord like this.
  4. rnlock
    Joined: Aug 2016
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    Location: Massachusetts

    rnlock Junior Member

    If everything is scaled exactly, the model won't be able to sail in anywhere near as much wind as the full scale would. On the other hand, at 1/4 the height, the wind is much weaker. Or you can sail it on days which don't have much wind. The model's hull speed should be 1/2 that of the full scale.

    I think one thing your model will be good for is hydrostatics. You can figure out just where it needs to balance and how heavy it should be to float on its lines. You can also determine righting moment by experiment. Because of viscous effects, the model won't point as high. I think the model might help with weather and lee helm.

    Lots of models have ridiculously tall rigs. This is part of why they need ridiculously deep fins (keels). If on the other hand, you look at the Soling 1 meter, it has a fairly normal looking rig and a fairly normal looking keel. That keel is kind of fat, but the model will stand up to a fair amount of wind. Not as much need,for smaller rigs on windy days.

  5. Howlandwoodworks
    Joined: Sep 2018
    Posts: 145
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    Location: MO

    Howlandwoodworks Member

    Thanks for your in sites, I need all the help I can get.
    The model is not meant to sail, it is just a 3D model for my design. I am using it as a (*Mind tool for my ** Necktop computer as a Intuitive pump)
    and as a check and balance for my calculations such as CB, LWL, how planks would be shaped and cut, ribbing and molds margin of error to achieve a fair hull ...
    I was hoping to use it to calculate a Approximating GM for the #@$% Dellenbaugh angle, but how to scale the roll period up from 1/4 scale is still alluding me. Any thoughts would be welcomed?

    John Howland

    *David Jonassen - coined phrase
    **Daniel Dennett - coined phrases

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