Compound Curvature in Aluminum plate

Discussion in 'Metal Boat Building' started by fpjeepy05, Jul 23, 2019.

  1. fpjeepy05
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    fpjeepy05 Senior Member

    How is this done? I see sailboats with rounded bilges all made out of aluminum and "variable deadrise" aluminum powerboats. But most amateur builder plans are "plywood or aluminum" plans that are all developable surfaces.

    I googled as much as I could and didn't come up with much. "Tortured" relates to almost entirely plywood. "Warped plane" "compound curvature" these search results don't provide much. How much twist can be put in a sheet of aluminum? What does one do in the event that more twist is needed?

    Any books I can read that might shed a little light on this?
     
  2. KeithO
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    KeithO Senior Member

  3. DCockey
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    DCockey Senior Member

    Aluminum sheet can be forced into shapes which are not exactly developable but the possible deviation from developable is less than with plywood.

    Aluminum can be formed into compound curvature by several methods including using an English wheel. ds

    Some aluminum sailboats with rounded bilges, such as Dudley Dix's "radius chine" designs, use segmented cylindrical surfaces for the bilge with developable surfaces above and below. Article - Radius chine metal boat building https://www.dixdesign.com/radmetal.htm

    It is possible to design a variable deadrise boat with developable surfaces but the stations will not be exactly straight. However not all variable deadrise shapes are developable.
     
  4. fpjeepy05
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    fpjeepy05 Senior Member

    Cool. I think this answered my question a little bit. The surfaces are not developable, but they make it happen. [​IMG]

    I'm not interested in the actual building, I'm more interested in designing. But I can't design ff I don't know how it's built.
    Any way to quantify this?
    I'm failing to wrap my head around how it can be developable.
     
    Last edited: Jul 27, 2019
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    "it" meaning what ? What are you wanting to shape, that needs to be developable ?
     
  6. fpjeepy05
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    fpjeepy05 Senior Member

    Variable deadrise.

    The only developable surfaces are flat, cylindrical, conical or a variation of these. I’m trying to envision how one of these would be trimmed to be a close approximation of the twisting of a variable deadrise hull bottom.
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    You mean a boat with a curved bottom at the transom ? Good shape in many ways. DEV.jpg
     
  8. Ad Hoc
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    Ad Hoc Naval Architect

    He means like this.
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    He doesn't need compound curves to get the "variable deadrise" he is interested in. Or as I understand what he wants.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    He is talking about variable deadrise in the bottom, at the transom, not deadrise varying along the length, like a warped plane. He doesn't want straight sections aft. Failing that, I don't know what he wants !
     
  11. Ad Hoc
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    Ad Hoc Naval Architect

    He wasn't asking about that he was asking:

    Hence the link to hyperforming.
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    That will likely be beyond the scope of his activities, I suspect he is thinking he needs compound curves, and wants to know how to get it, but probably doesn't need them.
     
  13. fpjeepy05
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    fpjeepy05 Senior Member

    You are correct. I meant a warped hull. 60 degrees of deadrise forward and 5 degrees at the transom. (Exaggerated)
    You are also right that it can be done with developable surfaces, like you have drawn. It wouldn’t be the same shape as a tradition warped hull as the midsections would have an addition chime between the keel and chine, but I suspect the net affect would be similar. Adding a third sheet between the deadrise of the other two might make the transition less drastic. The midsections would then have two additional chines.
     
  14. fpjeepy05
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    fpjeepy05 Senior Member

    Additionally, I think I have came up with an idea to quantify twist. Modeling it as a simple beam in torsion. (although the cross-section of the beam is very long in one dimension and very short in the other.) I could apply a torque that could reasonably be applied. (say not more than the 100-200#) and see what angle the sheet would rotate (and check for yielding). It would be affected by the length along the twist axis, the width of the panel perpendicular to the axis, the thickness of the plate, and the material. It would be a cool to have a forumla that would give the angle of max rotation per foot for a given panel width and thickness. Then one could model any shape they wanted and then cut down panel sizes until it was twistable.

    Maybe I can dig up my old engineering books and plug through the numbers.
     

  15. DCockey
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    DCockey Senior Member

    Example of a developable surface hull with deadrise varying from bow to stern. Blue and green lines are ruling lines. None of the surfaces are flat, cylindrical or conical.
    Example 002-1.jpg Example 002-2.jpg
     
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