While many of the sites listed in this thread have some great-looking 3D models, many of them aren't designed for 3D printing, which is a complete subject unto itself. (Thingverse being the notable exception.)
Turbo-squid is an excellent source for high-quality assets often used in production. It's faster and far more economical to spend hundreds of dollars for a highly-detailed aircraft carrier that can be used as soon as it's downloaded than build it in-house for thousands over a months-long period. I was forced to do this a few times on projects when time was short on a looming deadline.
After a decade of modeling sci-fi, armor, ships and aircraft, I decided to concentrate my time/effort on the one subject I'm knowledgeable in: Nuclear submarines.
For one example, CG Trader has some nice-looking models, but want $900 to convert them to a printable model.
3D model is available for download ☝ ➦ in FBX, OBJ, 3DS, and C4D file formats, compatible with over 23 modeling software. Asset is ready for rendering.
3dmodels.org
That's a little steep when you consider the printed version only needs to be designed once, then re-sold at $900 a pop. All of the labor is complete except for the effort to operate a mouse to conduct the $ and file xfer. Not a bad business model if you have the clientele and more importantly, the assets potential customers want.
When I start a design, I spent an inordinate amount of time conducting research to make sure anyone who served on a particular class of boat would be satisfied with the detail. (I build submarines for submariners.) The final files are my IP and aren't for sale, because once they're out there, passing them around becomes a real issue.
Research and design takes at least six months of effort. The first printed boat is always a prototype and by the time it's finished, the design has been modified at least twice, using lessons learned during the build with an extensive build log to document the process.
My competition? Mahogany-lathed hulls from the Philipinnes, which cannot approach resin-printed detail and can sell for thousands once they reach 18" or longer. Yikes!
It isn't profitable producing low-volume parts. Display or RC models (completed or in kit form) for those who can't/don't print can be very profitable, if the quality is there. This company sells their STL files, but can't be completed without their PE parts, which reduces the chances of STL piracy. They do excellent research and work:
https://rcsubs.cz/
My latest project (1/72) for a museum display is nearly finished. It should be mounted on keel blocks next week. I have multiple boats waiting to be started for next year's schedule.
CC
