Well, bricks don't hang in the sky. They fall. These ships did the opposite of what bricks usually do. That's the beauty of Douglas Adams' wit. ;)

this sounds more like a sarcastic statement, i'm assuming you're reading a fiction story that involves flying ships, but anyways the author here wants to illustrate that there this ship in particular, which didn't reach the sky the same way a piece of brick can not reach the sky much less move on it's on own.

Sounds like poetry to me! I guess its describing the ships as lined up in the same way that bricks are?