It's probably on the level of combat mecha, but I always wondered if it would be possible to build a real life airship in the fantasy style. Essentially a sailing vessel attached to a drigible.
In terms of weight, it would certainly be doable. Just a matter of making the dirigible/blimp big enough.
In terms of functionality, I'm not sure. You're not going to land the dirigible on the ocean. You might be able to lower the sailing ship on a winch, but again, to what end?
Might be fun as a fantasy pirate ship. You think you're coming up on a big fat freighter, then the airbags deploy, and it lifts out of the water and starts dropping bombs...
I could also see it in an alt-history game where the age of sail went straight into dirigibles after the Montgolfier Brothers. England might take Heart of Oak and convert it into a dirigible just to piss off the French.