Hard chine dinghy hull, flat patterns?

Discussion in 'Software' started by rszemeti, Feb 19, 2012.

  1. rszemeti
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    rszemeti Junior Member

    Hi,

    I have drawn up a dinghy hull for plywood construction in Solidworks, and I have offset tables to the class rules etc .. what I need to do now is produce some .DXF flat patterns of the panels to cut on my CNC router.

    I tried the "carlson design" hull designer package, which looks like it shoudl work, but only accepts 5 frame positions int the offset tables ( I have 7 )

    Anyone care to recommend a (ideally free or cheap) package that can loft hard chine panels from a set of offset tables and output in .dxf?
     
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  2. lewisboats
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    lewisboats Obsessed Member

  3. rszemeti
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    rszemeti Junior Member

    Are you sure?

    Firstly, I cannot see how to limit the curvature of the surfaces in the XY plane to straight lines so they pass through the chine points.

    Secondly, unless I am mistaken, there is NO option of flat pattern output in FreeShip .. just a 3d DXF with frames ... no flat patterns of surface development the panels
     
  4. rszemeti
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    rszemeti Junior Member

    OK, I see how to make the hard chines

    Add creases to the chine lines .. yeah OK, that works.

    Now, how to get the developed flat patterns of the panels?
     
  5. lewisboats
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    lewisboats Obsessed Member

    Tools, Develop plates, export as dxf (picture of a compass or dividers)

    Note... to make panels show up as developable you have to go into layer properties and enable developable on each of the layers (if they aren't already)
     
  6. rszemeti
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    rszemeti Junior Member

    Ah, greyed out

    I can see I need to read the manual :) no doubt it will explain why the "develop surfaces" option is greyed out.

    The plate hull shape is still wierd ... I added creases to the chines, but looking on plan view, the shape still does not pass through the control points, it seems to be "rubber banded" inside them ... the points I have set in the offsets are the mid points of the measurement locations of the class rules, so it is essential the hull actually passes through those points ...
     
  7. lewisboats
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    lewisboats Obsessed Member

    The control points "pull" the line and so are not where the lines end up. Best way to get the lines to the exact points are to expand the view windows one at a time and put the cursor exactly on the line (look at the coords in the window bar). Pull the point and check with the line until the line hits the point you want in that view. Do the same in the other views and rotate around until they all agree with your offsets (if they don't already to start with).

    Re-read my last post about enabling developability.
     
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  8. rszemeti
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    rszemeti Junior Member

    I see ...

    I got the development to sort of work, it developed the first chine plate anyway, so I'll play with that.

    The chine points is more of a tricky issue ... I might try creating a "chines"file and importing it, as the manual seems to suggest that the "chines are fitted to the data points of each imported curve in such a way that the chines from freeShip match these curves"

    We shall see.

    Thanks for the assistance :)
     
  9. lewisboats
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    lewisboats Obsessed Member

    You are the fastest learner of freeship I have ever come across. You'll be teaching me in an hour or two.
     
  10. rszemeti
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    rszemeti Junior Member

    Years of experience with AutoCAD and more recently, Solidworks for solidmodelling .. oh and for the day job I am a Linux admin/developer .. :)
     
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  11. lewisboats
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    lewisboats Obsessed Member

    Piece of Cake....
     
  12. rszemeti
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    rszemeti Junior Member

    So .. the only remaining question is ...

    My design has a "pram" bow,

    like so:

    [​IMG]

    any ideas how to create a chines file to represent that, or how else to acheive it in freeship?

    Freeship worked great for the panels, just need to figure out the bow ...
     
  13. lewisboats
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    lewisboats Obsessed Member

    Good morning early riser!

    Take the bow point (s) and move them off to the side to the correct shape then extrude the edge back to the middle, fair up your lines. Highlight the line, edge, extrude, extrude in a negative direction (-1.375 or whatever) then take all your new points and make them y=0 to put them in the center again. Of course you will have to fair up the shear line and an intermediate lines ...the chine line shouldn't need anything but it might. To make sure your bow lines are straight use the align button. You will need 3 or more points on the line, select them in linear sequence then press the button. It will align the points between the first and last selected, thus assuring a straight line even at an angle. You should align the shear/chine line and the centerline of the bow transom top to bottom. This will give a flat panel that can be developed. Do not do this if you don't want the line to be straight in ALL directions... Undo is your friend, and so is save and save many different versions such as Skiff, Skiffa, Skiffb etc.
    Right click on a window, select mode and developability to see if the boat has issues with stretch or distortion (shows in red). The higher quality the view the less the red generally. If you get all green at lower res then you are sure to be good. Red edges are normal and not a problem so long as they don't extend into the panels. FS was developed for steel ship building and thin ply has greater twist/flex/stretch/compress -ability than sheet steel so a bit of red may not be a disaster. I have built boats that have red in the panels that still came out fine. Just depends on the amount and kind of distortion the red is highlighting.


    Pretty boat.
     
  14. rszemeti
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    rszemeti Junior Member

    hmmm

    OK, thats easy enough, I dont need the front piece so its just the skins im interested in.

    So ... I entered some rough values and worked up an offsets table .. split the bow and the linesplan looks pretty close. not been through the control points to check the fit against the rules, but, lets assume its close.

    The flat patterns for the plates seem to be .. wrong though. If you look at the side view, you can see the keel line curves up at the bow and stern, deepest around the mid section. Looking at the front elevation, you can see the slope of the sole plates towards the keel.

    So, I would expect the sole plates to have a convex curve along the keel line. Looking at the flat patterns, the edges are almost straight, and *concave* at the bow ... cutting them out and gluing them together produces a bowline in the sole plates that dips *down* at the bow, instead of up!! ...

    edit: convex/concave

    [​IMG]

    [​IMG]
     
    Last edited: Feb 20, 2012

  15. lewisboats
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    lewisboats Obsessed Member

    You have quite a bit of twist at the bow along the keel line...the panels look correct to me but I bet the error is significant. You are using quite a bit of surface area at the bow making the twist, flattening it out reveals the area. Go to Calculations/intersections and add some stations: Select +N and put in a spacing for the entire boat...say .5, then add +1 a couple of times towards the bow...say 3.625 3.75, 3.875 4.125. Turn off the control points with the "show control net" button, right click on the Body plan pane and save an image...post it here please. That should show the transition from near flat to near vertical. Oh...and ply doesn't like concave...convex yes but not concave. In order for it to be developable it must be able to be gotten out of a cone or a cylinder and concave shapes require too much compression to do that with. You may have to consider doing the bow section of the bottom in strip planking rather than out of plywood sheet.

    Take a picture of the perspective pane in Developability check mode showing the bottom a view just under the water off the SB bow quarter...like so:

    [​IMG]
     
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