Hi Circusdog!
I'm sort of excited to see someone else taking on the same project I did... ie, making the Enterprise in a CAD package.
I've got a finished Enterprise (well, finished EXTERNALLY, though I'm still building the internals as the mood hits me), done entirely in Pro/ENGINEER (Wildfire v4.0). I also chose to use Sinclair's drawings as my primary reference. I can give you quite a few "pointers" if you'd like them. Or you can just review my (old) thread...
http://www.trekbbs.com/showthread.php?t=89810
I have to point out, the "ribs" as you've "fixed" them, above, are incorrect. I had the same issue when I was making my own. I recommend going to posts 194 and 197 in my thread... this will be of some help to you.
There are significant parallels between what you're doing and what I did. By the way, I've worked with Autodesk Inventor extensively, though Pro/E has always been my tool of choice (with Solidworks my second choice). Inventor has one advantage over Pro/E... the ability to easily control constraints (Pro/E creates constraints on its own and you have to "outsmart" the software sometimes to make something other than what the software "thinks you really want".)
My first piece of advice is to use Alan's drawings as TEMPLATES. But to NOT simply use the drafting features of his work in your 3D model. Put the DXF import onto a layer, lock that layer, and then create your own sketches to do your shaping from. Trust me... it will come back to bite you later if you don't. His work is nice enough, overall... but there are some of his 2D draft entities which don't fully intersect with the entities they're supposed to connect to, and other cases where there is not true tangency between his draft entities when there should be. And in the case of complex curves, you'll find that they break down in some cases... and that you can create the same curvature using splines you draw yourself and get a much simpler, cleaner, and less-computationally-intensive model to boot.
His work was designed to be 2D. It's very NICE 2D work. But it's not really ideal for what you're doing. "Trace" his work, and you'll thank me later!
(FYI, I didn't even exactly do that... I used his work, but also drawings from several other sources, and made choices as to which I'd most closely emulate... and in some cases even deviated further from this when none of the available choices made perfect sense... such as the inconsistent "waterline markings" on the secondary hull, or the exact locations of windows, or the like.)
Now, about the B/C-deck superstructure... you can do this quite easily in Inventor... but not if you're trying to do it from the curves Sinclair provided. I tried that at first myself, and rapidly gave up (in fact, this is what convinced me to just redraw the entire revolved profile and only "trace" shapes, using my own CAD package's tools.)
The tool you need to use is a revolved sweep (I forget what it's called in Inventor, but the same feature is present in both Pro/E and Inventor). You'll need to create a set of curves to sweep around. The trick is to ensure that the curves match up "above the hull surface" but that you actually are creating the feature deeper in... I just did mine three meters below the "top" of the primary hull shape. I created a cylinder, the diameter of the bridge, first. I then revolved the front section, leaving a "pie with a wedge missing at the back." I then sketched the section... copying those edges but terminating below the surface, as I said, by three meters. I made sure that my "path" could be tweaked, later. I then just swept the profile. It didn't match the top-down blueprint shape exactly at first, so I had to tweak the parameters of the conic path (and the angle of the "missing pie wedge" for that matter) to get the shape, as seen from the top view and the side view, to be "just right." But it worked out quite nicely in the end, didn't it?
EDIT: Adding a link to the best reference post re: the ribs, to save you a few mouse-clicks:
http://www.trekbbs.com/showpost.php?p=2977846&postcount=197
