Those dwarves had almost every square inch of that boat covered in runes, and it still rode low in the water. The magic added to the buoyancy, but it wasn't enough to make it airborne. Nor would they have wanted it airborne. Dwarves aren't comfortable with heights. (Of course, they aren't supposed to be comfortable with water, either. But as I said, these guys were insane.) The sails were made from leather, actually. They were mostly for looks. The ship was propelled by oars. The pirates had a great con-job going, terrorizing passing ships in the fog, convincing them that a real dragon was attacking. They eventually tangled with the wrong band of adventurers. Frankly, I'm rather glad that the ship's at the bottom of the sea now. They were a rather silly lot. You're right. It does sound like something from Pratchett's Discworld.