Scaling Plans

Discussion in 'Boat Design' started by sean27, Oct 12, 2011.

  1. DCockey
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    DCockey Senior Member

    You might want to do some studying and learn how to layout a part from dimensions before trying to build a boat. It's a basic skill.
     
  2. sean27
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    sean27 Junior Member

    Chuck,

    THANK YOU!

    I will do just that. Draw it out on paper, cut out, layout on plywood drawn at same scale.

     
  3. sean27
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    sean27 Junior Member

    I know how to lay out the parts on paper/plywood, but was caught up in the thought that I had to draw out the new scaled up plan in some kind of cad/computer program. I am going to take Chuck's advice and draw it all up on paper with the new dimensions at 1/10 scale and do the nesting plan manually.
     
  4. DCockey
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    DCockey Senior Member

    Good to hear. It's understandable that you might think it should be done on a computer give some of the discussion here with folks who seem to believe that software is the key element for boat design.

    Some designers such as Phil Bolger work hard when designing a plywood boat to maximize the use of each sheet of plywood. If that's true for the design you are interested in then you will probably find the amount of plywood needed after enlarging goes up more than expected.

    After you get the parts laid out consider building a simple model using cardboard. It will help in learning how the boat goes together.
     
  5. philSweet
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    philSweet Senior Member

    Sean, very briefly, can you tell us why you want to enlarge this design? Do you want to fit in an additional feature, or do you feel the boat as designed is built for munchkins and you need more elbow room. Maybe you just have a bigger trailer at your disposal. The way boats scale, one would not ordinarily just apply a fixed factor to everything. Seats, bunks, headroom might best be left alone. You must be careful how the joinery work comes together in this case. Stretching only the length is usually the easiest thing to do because most designs have already pushed the panel width to the max. However, it is not simply a matter of stretching the panel flats since the angles all change. I'm guessing that's what you meant by saying a bulk scaling factor was all you knew how to accomplish. Please be conscious of preserving the original design's grain orientation and good face up orientations when creating the new nesting. You can't just nest them any old way. Also check the mechanicals. Will the motor mount still serve or was it at its limit geometrically, you may require a longer shaft. Will the standard control cables still work or do you now need an extended set. You'll have to think about how the glass sheath goes on as well regards the overlaps and reinforcements.
     
  6. michael pierzga
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    michael pierzga Senior Member

    Sounds like sensible advice. That boat looks a good candidate for stretching.

    Also by simply stretching the boat 8 percent , you can preserve much of the original ply nesting.

    As was noted grain orientation is worth considering when you re nest. Some components care little, some need grain respected.
     
  7. DCockey
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    DCockey Senior Member

    Be aware that if the design is stretched in length only, the shapes of the panels will fundamentally change, not simply stretch in one direction. The expansion of the surfaces to obtain the shapes must then be redone. This is a task which good software can greatly simplify.
     
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  8. michael pierzga
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    michael pierzga Senior Member

    Sure, But stretching the hull panels is straightforward. That's a 4 panel boat plus a transom.
    I would have no idea how to go about stretching all the interior, cabin components.

    Its these components that the original design nesting plan is most useful for.
     
  9. DCockey
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    DCockey Senior Member

    Stretching the hull panels is not straightforward if the design is stretched in only one or two directions (unless the design is a scow with parallel sides). The distances along the hull do not scale with the the length because the hull is curved.
     
  10. michael pierzga
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    michael pierzga Senior Member

    Ya, sure... but youre talking about drawing, lofting on a computer. I dont have any computer skils.
    I would simply set the frame or frames at B max plus transom on the jig , play around with a long batten batten until I got the stretch propotions correct, then measure for the ply panels. Its how I added to the last skiff. For me Its the easiest way.

    I guess is a good intellectual challenge to master the computer, but Id have to spend weeks just learning how to use the software and even then my eye just cant "see" on a computer.
     
  11. michael pierzga
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    michael pierzga Senior Member

    I guess the big question is why stretch the design to begin with ? On my skiff I needed just a bit more buoyancy aft to float the new, heavy 4 stroke outboard and keep the skiff on her lines.
     
  12. sean27
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    sean27 Junior Member

    After thinking about it, I am not going to scale the design. The boat is large enough for what I need it for and all the potential risks that go along with scaling a plan will be eliminated.

    I have started a model.

    [​IMG]
     
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  13. philSweet
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    philSweet Senior Member

    Excellent. you will soon notice that the panels will not lay exactly flat against a dead straight frame edge. The frames should have a small bow to the faces. In this design I think it will be quite small, but the frames should be eased to accommodate the shape of the panels. On the real boat don't draw the panel flat against the frame if it doesn't lay that way, you will create and ugly hump somewhere. There is a paper attached which explains a graphical way to develop the amount of bow on the frame. Or you can just adjust during the build. The plans should explain how they want you to deal with this. Hopefully, they have given you the curved shape on the plans.
     

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