Existing hull import problems

[Roger Long]

I am trying to use Delftship with existing faired lines for rendering and to take advantage of the advanced hydrostatic features. Some of these will be historic vessels so a high degree of fidelity to the original design is required. I’m working from faired AutoCAD sources so I need to use numerical import.

It appears that the imported lines are used to define the control net and those then define the mesh surfaces. I can see the lines I input as magenta lines but the program seems to ignore them and draw new lines according to its fairing routines (that I can’t find a way to turn off).

Is there anyway to force the sheer and fairbody lines I import through text files to be treated as control lines and force the surface edges through them?

[Marven]

No you can’t.

But you have to bear in mind that the control points are not on the surface, there’s always a distance between the control points and the actual surface. This complicates things.

The best way to model existing vessels is to use background lines or images and then keep adjusting the model until the lines correspond to the background geometry. This way you have more control over the amount of control points and their distribution over the surface.

[Roger Long]

That’s a real shame and one that could probably be fixed with a check box that turns off the automatic fairing and some programing to draw the meshes through the input curves as can be done with AutoCAD and Rhino.

I have often had to prepare stability data for existing vessel that are not actually fair. The Coast Guard doesn’t care if the lines are fair, they want to be sure they accurately reflect the existing vessel. The errors inherent in scanning and tracing an image would be unacceptable to them and the labor would be prohibitive.

[Marven]

Roger Long wrote:

The errors inherent in scanning and tracing an image would be unacceptable to them and the labor would be prohibitive.

Not neccesarily. It depends on the quality of your image. Of course a small image would not be of sufficient quality, where larger images are. Instead of images you could also use markers (vector curves) to use as background geometry. Whether you are reproducing an existing lines plan or a real-life model (which is possible not very fair anymore due to distortions ) doesn’t really matter as long as your background geometry reflects the target model accurately.

As far as labour is concerned, I happen to do this type of work a lot and can recreate almost any model in a matter of hours.

[Bruce Packard]

Insisting on control points out in space puts a crimp on importing an exsisting design into this program. Other design programs have found a way to work with points on the hull surface, it is time to bring your program up to date and easier to use.

[Roger Long]

Many hours later, I’ve figured out how to make the program work with existing hulls. Importing separate surfaces with the rows and columns numbers set fairly high does it and it is reasonably easy to produce the import text files by cut and paste from the AutoCad properties window after tracing the lines with polylines.

I was able to produce this model:

[Marven]

Nicely done!

[Fred Rosse]

I notice you are replicating older hulls. I would like to get, if possible, some of the older hull models, such as the WWII Liberty ship, English steam coasters and trawlers, steel lifeboats of WWII era, etc. Do you know of any source that might be available in Delftship format, or other sources?

Thanks in advance

[Author]

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