Building of Aluminium Boat . Mounting of hull framing structure

Discussion in 'Boat Design' started by an2reir, Feb 27, 2019.

  1. Barry
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    Barry Senior Member

    So if then you wanted to Chamfer for tight fitment, you would need a multi axis, waterjet, plasma or router table for this?
     
  2. Barry
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    Barry Senior Member

    Giving more consideration about how to ensure the precision of each shell that you build to enable you to use a preformed inner structure, I would still utilize the bolts to affix the shell to the
    frame but also add a few studs that are welded upwards from the steel jig, and when the plates are cut, have corresponding holes cut into the plate. Might be a little tricky around the bow but these stud/hole combination would ensure precision/repeatability. IE place the hull bottom and sides within mm of each other from boat to boat.

    Additionally, I would consider a 1/4 inch bottom to help with keeping the hull bottom straight. There would be added weight but you may be able to save some in your
    stringer build.

    What alloy are you using? And MIG only? Not TIG
     
  3. DCockey
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    DCockey Senior Member

    If that type of equipment is available then the chamfers can be modeled in Rhino for input to the software which generates the control file for the cutter. If the chamfers will be manually created with a handheld grinder, etc then the model with the chamfers can be used to ensure the plate is cut large enough to create the chamfers. Or the plate can be modeled with square edges and the size of the gaps will be visible.
     
  4. gonzo
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    gonzo Senior Member

    I determine it by the way the plating lays on the frames. If it was completely developable into a shape has straight transverse sections, this thread would not exist. However, it lays against the frames up to the point where the chine start to go up. From there on, it is not developable into the designed shape. One way to make the plate lay flat on the frames is to cut it into triangles and make compound conical shapes that approximate the designed lines. The other is to cut longitudinal strips that are lofted to create the designed shape.
     
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  5. an2reir
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    an2reir fifty boat designs

    I just did another test. Lowell Walmsley the author of the DevSrf software was so very kind as to make a developable surface on my hull bottom lines. His developable surface is silghtly different than mine. But when unrolled the two are totally identical. The bottom plates, boat lines and the frames cutting files would be identical. That is a fourth validation . Gonzo thanks for feedback the thread would still exist if the builing of the hull bottom was done in such way that the contraction of the welds at the center when cooling did slightly warp the boat bottom pulling the tip upwards and incraesing the hull bottom sides curvature.
     

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  6. gonzo
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    gonzo Senior Member

    Have you tried making a model in cardboard? Forget software and see if it can actually lay flat on the frames. It shouldn't take you more than 30 minutes or so.
     
  7. an2reir
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    an2reir fifty boat designs

    Hi Gonzo, made one 580 mm LOA - in steel plate 3mm thickness and did work allright
     

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  8. TANSL
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    TANSL Senior Member

    If one knows how to use the right software, for this type of boat, you do not need to make any scale model and the software is always much faster. If one does not know how to use the software it is logical that he has no choice but to build scale models.
    For what Andrei has just explained to us (same results with two different software), it seems clear that it is a problem of bad sequence of assembly and welding.
    Imo, the solution of the triangles (I suppose you mean spherical triangles) will always be worse and much more expensive than making the plates again.
     
  9. Ad Hoc
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    Ad Hoc Naval Architect

    Sorry, but you're now starting to use all the wrong "tools" for a simple job!
    FEA is not the right tool here...

    You just need some curvature in those fwd frames, to allow a simple developable plate, that's all.
     
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  10. gonzo
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    gonzo Senior Member

    Looks like the panels should lay on the frames nicely. That means that the way the plates got cut, welded or both ended up distorting them. I suppose you can cut the welds and lay the plate on the frames. Unfortunately you may need to add a piece on one of the edges.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    No shape that has non-parallel straight sections, is strictly developable.
     
  12. Ad Hoc
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    Ad Hoc Naval Architect

    Forgive the crude nature of the sketch, but just attempting to lift off some basic dimensions (from your images) and place them in plan view and profile view:

    upload_2019-3-2_8-33-8.png

    You don't have a constant rate of curvature between sections when laid flat. This suggest the plate will not take the shape you desire without being stretched in different directions, i.e. a complex curve not straight.
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    I'd say many plate builders would love to easily replicate the OP's lines, it would be a good boat in my opinion, but alas they are stuck with compromises that don't look much different to the casual observer, but do not ride as well. One high volume builder in Australia has invested in stretch-forming to get hollow flared bows, and even the bottom forward has slight concavity. Whether that is done with tempered sheet, I don't know, maybe a softer material is needed to work into those shapes.
     
  14. an2reir
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    an2reir fifty boat designs

    Hi there, thank you for your feedback. To answer to above AdHoc : I think my bottom plate is developable as it did unroll in three different software and the unrolled cutting file does match perfectly the one unrolled from a developable surface made by Lowell Walmsley. I am reading what you wrote and I did replicate your drawing in the sketch . But even before that I can say that the developable surface made by Lowell Walmsley does match perfectly both my Profile the chine line and the keel line as well as my plan view . In this case your above reasoning should apply equally to the developable surface designed by him as well with his own software tools. I wonder can this be so ??? because his is a certain and 100% developable surface. But then I do uderstand from your above that the rule you illustrated is intended to be indicative to a geometry " being buildable in metal plate" and not necessarily to the geometry being a "developable surface " . In regards my use of computer simulation to check if a particular bottom plate cut from aluminium will curve on the framing; yes of course I am fully aware the FEA software was not designed for this specific purpose, nonetheless , what FEA does is it does simuate the deformation of a structure made of a particular material of precise mechanical properties when subjected to a set of forces and constrained by a given set of constraints. As I am doing anyway the FEA simulation of my bottom structure to validate its strenght - I was thinking as well in this direction of setting up loadcases in wich I would replicate the mounting sequence of a bottom plate on its curved bottom framing.
     

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    Last edited: Mar 2, 2019

  15. gonzo
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    gonzo Senior Member

    If the plates are developable (they will lay on transverse straight frames) the forces on the plate should all be normal. FEA will indeed do what you describe. However, it won't show if the shape will develop or not.
     
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