balloons are used in airships with a hot-air system to lift the ship into the air.
and you need a TON of hot air to be able to provide enough lift for even the smallest of weight. that balloon should be at least double the size of the actual ship, and not half of it.
You're thinking of the other kind of balloon-based airship. This ship is more of a zeppelin, based on the shape of the balloon (is longer than it is tall) which utilizes the lighter-than-air hydrogen to lift the airship. In which case, it is about twenty times too small.
But because fantasy is some kind of forgeted up, your balloon is just the right size for that craft, though I would suggest you round out the hull a bit.
