Discworld – Jingo (Terry Pratchett)

Water dripped off the Boat's metal ceiling and blobbed on to the paper in front of Leonard of QuirmHe wiped it away. It might have been boring, waiting in a small metal can under a nondescript jetty, but Leonard had no concept of the term.

Absentmindedly, he jotted a brief sketch of an improved ventilation system.

He started to watch his own hand. Almost without his guidance, taking its instructions from somewhere else in his head, it drew a cutaway of a much larger version of the Boat. Here, here and here... there could be a bank of a hundred oars rather than pedals, each one manned – his pencil caressed the paper – by a well muscled and not overdressed young warrior. A boat that would pass unseen under other boats, take men wherever they needed to go. Here a giant saw, affixed to the roof, so that when rowed at speed it could cut the hulls of enemy ships. And here and here a tube...

He stopped and stared at his drawing for a while. Then he sighed and started to tear it up.