Nice entries on first and second places. I don't know what to say about the third one, poor rendering, maybe the concept shows some potential, but it still seems very loose to me.
The fourth one has a nice atmosphere and nice rendering, but where is the concept? A classic pirate ship sustained by a balloon?? What happened to the "all that needs to be clear is that this behemoth is airborne and impressive in both its defenses and weaponry." ??? It doesn't look like a fortress, it doesn't look like it has heavy defenses... it looks like one well placed hit can bring it down right away...
I'd really like a better brief and maybe you guys could also take into consideration what Alex is writing in there, otherwise stop giving details like "impressive in both its defenses and weaponry".
Anyway, congrats to the winners.