Building a small work barge with plywood

Discussion in 'Boat Design' started by indianbayjoe, Nov 20, 2010.

  1. CaptBill
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    CaptBill CaptBill

    You have the right idea with the honeycomb sections now you need to lay it out on the RIGHT grid system. If you use a golden section grid much of the engineering is handled for you. A barge would be easy for this style of build.

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  2. SamSam
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    SamSam Senior Member

    I'm not quite sure what the RIGHT grid system is. Your grid system to me ( just an intuitive guess) would seem to be opposite of what actual stresses would be. The center would seem to be where the highest stresses would be. What do the heavier lines in the top illustration illustrate?

    Also, with this or any grid system, how tall is the grid? A barge can be a hull with just a bottom and top, a working platform, or it can have an insides, something you can put something into. To have an inside usability would be handy, it can always easily be decked to have a platform.
     
  3. CaptBill
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    CaptBill CaptBill

    Hi Sam,
    I was rather ambiguous in the example. The sketch up I did is rather incomplete. It is showing the main support backbone. The center of gravity is shifted forward and members come together where the crane shares support(circle). My thinking was go light aft and leave some overhang then she would maneuver like a duck. The bow quarter is raised, cargo area deck height should be as low as possible but above waterline. That was the idea.

    Concerning center as the strongest goes: actually the grid is mirrored on each side so we actually want to split the center board and take it in each direction to the first "chord", which is much stronger than the center alone. Plus more importantly, energy transfer/dissipation issues are accounted for. Notice the spacing of the grid is spaced like a guitar fretboard. The "bridge points" are now connected harmonically and work in concert to resonate the energy evenly throughout the structure like a musical instrument resonates. All that,as complicated as it sounds, you are getting by accident using the phi grid.


    I meant "right" grid for us backyard builders without engineering degrees,ha ha. By using a Phi grid you get a built in engineering "training wheels" of sorts. We are eliminating the infinite points within a 3d space and singling out the golden points. Now we can pull curves, compound curves even, without a problem. The NACA foil itself is based on the Phi ratio. So a perfect naca foil is naturally produced staring you in the face. Plus consider this: we only have 12 different measurements with this particular grid. 12 measurements. So I can precut these measurements. Make a stack of these "measuring sticks" and leave my measuring tape in the toolbox.

    I have Rhino Grasshopper scripts if anyone is interested.

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  4. CaptBill
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    CaptBill CaptBill

    Quote
    "Also, with this or any grid system, how tall is the grid? A barge can be a hull with just a bottom and top, a working platform, or it can have an insides, something you can put something into. To have an inside usability would be handy, it can always easily be decked to have a platform."

    The grid is any size you define and works in 3d. But in reality you would,say, find 3 bare walls (One for X, Y, and Z), lay out the grid on the walls. and use the intersection points. Drive nails at the points and use thin strips of wood to compose your curves.

    Sounds rather complex but actually this make it childs play. Hardest part will be laying out the grid. After that you are of to the races. You build out composite trusses in effect in an assembly line fashion

    [​IMG]
     
  5. SamSam
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    SamSam Senior Member

    I made some banjos and I think the fret spacing process was to take the space between the nut and the bridge and put the first fret at 1/25th of that space. The second fret went at 1/25th of the remaining space, the third at 1/25th of that remaining space and so on until you were at the end of the fretboard, every space smaller than the last but all on some sort of identical mathematical path.

    I'm not quite sure how closely a barge has to be tuned though.
     
  6. SamSam
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    SamSam Senior Member

  7. CaptBill
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    CaptBill CaptBill

    Yeah that's the idea except he put the motor on backwards...maybe he is just demonstrating reverse
     
  8. indianbayjoe
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    indianbayjoe Senior Member

    Boy, you guys are way ahead of me.. Were still working in the dark ages with a drafting board and pencil and paper. I will try and copy some of the drawings that Chick has made and post them. Not sure how since they are 24" X 30" but maybe i can take a picture of them. Don't know of anyone around with a scanner that large. Were continually working on our design taking into account some info from you guys and our experiences. Chick did have compartments that were scuppered but not accessible and not i have asked him to add pass through holes through the bulkheads to allow for inspection and repair. The craft would end up with 4 separate compartments. We are planning on utilizing some of that area for storage of things like chains, blocks, lines etc. Also we will probably ballast the aft end of the barge a little. This should help when lifting a large load up forward. In our design we had the lateral bulkheads spaced every 2 feet. The longitudinal bulkheads will be every 4 feet. All internal construction is double 3/4 ply glassed and sealed.
    I need to look into that program that your using captbill.
     
  9. SamSam
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    SamSam Senior Member

    I can't follow it either.

    For ballast you could have some tanks (old hot water tanks) that you could fill and empty easily.
     
  10. MatthewDS
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    MatthewDS Senior Member

    @CaptBill, Your render in post #106 shows a structure where the frames are farthest apart at the midpoint of the barge, similarly your longitudinals are widely spaced at the centerline, and close together near the outer edges.

    Assuming a point load on center of the barge (some equipment), the highest moment in the structure will be in the direct center. As a result, the highest stress will be found in the bottom hull skin, in the direct center. Your layout shows this area to have the longest unbraced length for both frames and longitudinals, which is absurd.

    Why on earth would you cluster your members into the area of least stress, while leaving the most highly stressed portions unreinforced? Please don't spread bad information.
     
  11. SamSam
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    SamSam Senior Member

    Even unloaded it's stressed from below, hogging wise.
     
  12. hoytedow
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    hoytedow Carbon Based Life Form

    Tighten the guitar strings to diminish hogging. :D
     
  13. rwatson
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    rwatson Senior Member

    I always understood that the 'golden' er ... concept was mainly for aesthetics and a common feature of exponential organic growth - I had never heard of it being used in engineering calculations like this
     
  14. wardd
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    wardd Senior Member

    now you have
     

  15. SamSam
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    SamSam Senior Member

    There's a name for those guitar string anti hog cable doodads. ???

    I found it, it's a hogging post with a cable brace.

    [​IMG]
     
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