The Ship Model Forum

I have used DesignCAD since 1987, and there are a number of tricks I use to hold down file size. Nevertheless, my USS Oklahoma City CLG-5 model is more than 500 Mbytes (I am modeling 1:1 with every feature 1/4" or larger, so there is a huge number of little pieces like nuts, bolts and screws). I expect it to be close to a gigabyte when it is done.

1. With extrusions along a curve - like railings, cable runs, pipes, etc. - the program defaults to a large number of sections to create very smooth solids. A single hand rail on a ladder will be about 13 Mbytes! I override the defaults and reduce the number of sections to the bare minimum that still produces a smooth looking surface at a "normal" viewing distance. The same hand rail will be 1-2 kbytes or so.

2. I break up pipes into straight sections and curved sections and create them separately. I use simple cylinders for the straight sections - this makes the file much smaller than the normal straight extrusion. For the curved parts where the curve has a constant radius I use a swept planar cross sections instead of extrusions. Again, I can control the number of steps in the sweep to get a good result with minimum file size increase.

3. Solids with complex curved surfaces gobble memory. If a curved surface is hidden - against another surface for example, I explode the solid and delete the hidden surface grid. Then I recombine the remaining parts into a faux solid (one side open). This often almost halves the memory needed for the part. Don't do this if you are planning on generating 3D stereolith files from the CAD model!

4. For cable runs I cheat. I don't use circular cross sections. Instead I use an octagonal plane and extrude it along a curve. If you look very closely it is ugly, but from even a moderate distance rendering artifacts make it look more like a braided cable than a smooth cylinder does, and the octagonal surface uses less memory and renders faster.

5. I build parts of the model (winches, boats, individual deck houses, hull, props and prop shafts, etc.) in separate files. It is much easier and faster to work in a 10-20 Mbyte file than it is to work with a 250 Mbyte file. Each is a separate project. Only when I need a complete assembly do I put all the pieces together, and I don't do any significant editing in the assembly file.

6. For complex assemblies like winches I create parts in many layers and disable everything I don't need in order to speed rendering, rotation, etc. After the whole assembly is completed I copy it to the larger file it will be a part of, and there I collapse the whole assembly (winch, boat, searchlight, etc.) into a single layer, and a single group. In the larger file it is just a single part. If it needs editing I work in the original file and not in the larger composite file.

7. I tried the trick of not combining solids, especially with hand rails. This created two problems. First, when I try to make a 2D drawing the intersections of the surfaces will be missing. It looks wierd. Second, you cannot create stereolith files from these "irrational" solids.

Did the test
Sample railing with solids - 432kB
Sample railing with extruded polylines and splines - 218kB
So the difference is significant.
Both drawings had the same settings, scale and all display settings.
Solids history was purged (btw history purge decreased size from 449kB to 432kB)
You can judge the difference in render appearance (poly on the left, solid on the right)

I think I see what your getting at, I thought you meant polygonal surfaces, not polylines. I haven't tried it but it might be a good idea. I have done plenty of sweeps in ACAD (ask Tim about my flexible tubing ). I have also used thick colored splines in 2D drawings to show wire routing in very complex control panel wiring diagrams. But I don't think I ever used polylines or splines in a render.

Why don't you try it. Save a file with plines, then render it. Then "Save as" a copy and extrude a circular profile along the pline. Save it and render. Post the results and let the crowd see how it turns out because I am intrigued now. Tim will tell you I really like finding shortcuts like this, even if I don't use ACAD much anymore.

Also, this is the only ACAD tip I remember. If you have items that are not selectable, hidden, or just plain not there but they are keeping you from purging a layer, then use qselect to select everything on the layer. You can the delete it while it is selected. Tim and I had some files that had this problem. We would try to purge layers but for some reason they wouldn't purge. Then I learned about qselect and it took care of the problem. That is the only tip I remember about purging.

Layers - yeap, got them. In my structural work you have to have 100s of them if you like it or not, company policy. Same with xrefs. So I use them also in my models. Hard to organize anything without layers.
With the railings I was getting at something else - I do it in solids mostly, but recently realized that making them from thick poly will still render ok for some views, but may be less memory consuming. I need to do some tests.
As for not merging solids, you're right it saves some bits but may create artifacts with renders.

ACAD has xrefs and layers, which if you are not already using those, get started! As for the railing, solids are fine, but keep in mind every time it intersects with a guard rail stanchion, it makes the file slightly bigger because there are now more edges and points that it has to calculate. The video card has to work slightly harder for no real gain in image quality. Best to extrude or sweep your rail but not allow it to merge or combine with the stanchions. In fact, any time you don't need to merge two parts you have the opportunity to decrease the file size slightly. They all add up. Some things, like your hull, you want to be one solid object, but there are many things that don't need to be.

Not sure if Acad has this feature, But in KeyCreator there is an "assembly"feature. It allows you to work in sub assemblies as separate files. The sub assemblies are then referenced by the master file. While working in the master file, the assemblies that are not needed for viewing at the moment can be "Ghosted" so that they are only represented by a bounding box, and not eating up CPU time with their graphics. It also helps to keep the master file size down. Of course this doesn't always help with complex solids (any solid defined by compound and complex Splines, Nurbs or otherwise) like a hull itself (especially if it has a lot of integral detail).

Another Solution is to work in scale. For in our office we almost exclusively work in 1/12 scale (i.e. 1 unit = a foot instead of an inch), this standard we devoloped years ago as most of our hydrostatics programs run with cubic feet. Also made it easier to plot in engineering scales. For 1/8"=1'-0" Plot simply export in 1/8, etc.

Hope this helps.

I have a decent machine but nothing special.
Not long ago I've learned about 3GB switch for XP and this saved me with Bradley as with out it Acad would not render this file.
Yeah, I'm purging everything I can (including solid history as I'm working almost exclusively with solids).
BTW - I wonder if railing from poly (extruded or with width) is beneficial - memory wise - as compared to solid railing.

You shoulda seen that one.

In SolidWorks the file size can get quite large, especially for hulls. The dumb file (with all the parametric stuff stripped out) for Scharnhorst's hull is over 300 mbs. The parametric one is nearly a Gb. I have learned to make them better since but they are always huge compared to most parts. If you are going to do CAD you need a big computer with a lot of memory. I know this isn't always an option, but it is the best solution.

If your working in solids, use the Brep command to purge shape history from the objects. I am sure you are aware of the purge command to remove unreferenced blocks, shapes, and dims. Also Never, never, never try to model true to scale diamond plate on a deck.

Sorry if this question was asked before:
How do you guys manage your projects when the file is getting large, say tens of MBs
Talking about ACad here but I guess the issue is also valid for other programs, isn't it?