Stations vs shadows

[Symont]

Hi

Reviewing the many informative and excellent threads here have been a great source of inspiration. A big thanks to all the contributors.

I am trying to create a model of a sailboat out of PDF’s coming from the original 2D CAD plan. I therefore made jpgs out of the profile and plan view to be imported as background. The stations were placed at each shadows of the hull. I think I may mix up the definition of the English vocabulary or maybe I don’t understand something more fundamental but… here is my dilemma:

The purple arrow shows an example of a known point on the hull (stern view, Y&Z axis), based on known coordinates. The edges and WL points were hardcoded and great (!), they match the imported background shadows lines (green arrow). The in between points were placed visually. The red arrow seems to represents a station line. It is a pretty obvious deduction since I can remove these lines with the button “Toggle stations visibility ON/OFF”. In my head, station = shadow (or a cut or a slice of the hull). So… I would believe that the red line should/must match the green line. I can easily make them perfectly matched if I move a couple of my known points a bit (keeping the same X coordinates). But then my know points would be “out” of the hull shell, which seems to defeat the purpose. Unless these points are construction “nods” that have nothing to do with physical point on the surface of the hull.

What do I don’t understand? Thank you for your time!

[Rob Hewitt]

Hi Symont
you are correct in your assumption the line you have marked as green is the control mesh and the hull profile will lie within those lines. Stations are slices of the actual hull profile.

[Symont]

Thanks Hewitt for your quick reply!

I am sorry to report that I am still confuse. Probably because I don’t understand the true meaning of a control mesh.

Does it mean that the points are “control” points that only define the surface and can therefore be offset from the actual hull surface in order to define the curvature/shape of that region?

If that is true, then I understand that I should match the stations and imported shadow lines, not worrying about the actual placement of the points. Is that correct?

Oh, and should I then checked the “corner” checkbox for the edge points?

[Rob Hewitt]

Hi
yes your are correct the control points can be offset from the true hull lines and you are also correct in your assumption regarding of matching the stations to your lines. If you are producing a hard chine hull then use the crease edge button to produce hard edges or knuckle lines on your hull if your hull is a curved carvel profile then do not.

[Symont]

In the light of your little explanation, I just reread the “Background to surface modeling” in the manual and everything seems clearer now.

Set sails!

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