More realistically you would one-off something like a boat out of fiberglass or carbon fiber and a non-metal mold (either shaped wood or foam, both of which can be large-scale milled easily). Yes, it would be more expensive than 3D printing, but a hell of a lot cheaper than an injection mold and with far better material properties than any thermoplastic. Or do it with vacuum forming. Injection molds are expensive because they are specifically designed and made for high-volume production with tight tolerances. If you don't need those things there are much cheaper options.
I'm personally bullish on 3D printing long-term, but FDM mostly still sucks and gets a lot more positive press than actual practical use in industry. It's just the easiest and cheapest of the printing technologies to expand on, so you see a lot of concept projects that sound good on paper.
I'm personally bullish on 3D printing long-term, but FDM mostly still sucks and gets a lot more positive press than actual practical use in industry. It's just the easiest and cheapest of the printing technologies to expand on, so you see a lot of concept projects that sound good on paper.