Free CAD program

[xanthar]

On 6/19/2024 at 1:52 AM, IronShips said:

To create hull shapes in 3D, Jaager is right, a NURBS modeler is needed.

 

 

I'm not disagreeing that NURBS make this easier but, It's not strictly a requirement.  The curves workshop in FreeCAD does use actually employ NURBS so, it fits the bill anyway.  One can get closer to an accurate hull from tracing a set of body lines or importing a table of offsets in FreeCAD because the curves workbench's tools will create splines that actually pass through those points and you can then use a Gordon surface to "loft" those splines together into a fair hull shape.  Delftship on the other hand interprets your coordinates as "control points" and the curves will almost never pass through them : (

[CDR_Ret]

2 hours ago, xanthar said:

Delftship on the other hand interprets your coordinates as "control points" and the curves will almost never pass through them : (

What you say is true, @xanthar, but the program uses a whole different approach to generating a surface, which I'm sure you are aware of. (When people talk about NURBS, my eyes glaze over . . .) In order to create an accurate and fair surface, you must introduce "intersections" that correspond to the lines on the plans you are working with. Once the applicable station, waterline, buttock, and diagonal coordinates are entered into the Intersections tool, and Intersections are enabled for the hull layer you are working with, simply moving the control points until the intersection lines align to the applicable lines on the plans creates the desired hull surface (and there are some basic rules for doing this). DELFTship control points almost never lie on the actual surface you are forming. The greater the curvature of the surface, the more intersection lines (and control points) you will need. This may require displaying more station, water, or buttock lines than the reference plans may contain, which is where fairing tools come in.

 

DELFTship has a whole bunch of fairing tools (i.e., basic shading, developable surfaces, Gaussian surfaces, zebra stripes, and environmental reflections) that involve various visual cues, including highlights, colors, and reflection patterns, to create a smooth, fair surface. After iteratively adjusting the hull surface to a visually or Gaussian fair form, you will likely find that the principle intersection lines don't exactly agree with the reference plan lines, as noted earlier in this thread. This is mainly due to the fact that taking off lines and converting them to 2D lines plans was as much an art as a science. The fidelity of the process depends on many factors, including the skill of the yard workers and draftsmen, the age of the original plans themselves (older physical drawings tend to shrink and warp with time), and physical factors pertaining to the hull, such as hogging, or perhaps the original hull wasn't perfectly fair in the first place. (My project's hull had a five-inch hog over 135 feet—which I ignored!)

 

Another feature that affects the fairness of a DELFTship model surface is the "Precision" setting. The higher the precision, the more sensitive the fairing tools are to adjustments, and the more fair the surface will be. I haven't tested this, but I believe the higher the precision setting, the finer the exported STL mesh will be as well (in the Free version).

 

Once you have an accurate, fair hull, you can export the file to another 3D program of your choice, confident that the basic hull form will provide a valid base for the rest of the model. I wouldn't bother using DELFTship for smaller details, though you can create them in DELFTship (I did). It's not designed for that—it's primarily a naval architectural program to evaluate the form and physics of modern vessel hulls and superstructures. For this reason, a lot of modeling features one would expect to be included in a 3D CAD program are either absent or work in such a klugey manner that they can drive you to distraction. PM me if you want to learn how to work around some of these so-called DELFTship "features."

 

Terry