Windlass

You are the volunteer keeper of the Twinney flight, a heritage staircase of English canal locks, for one summer. It is painted as a storybook gouache cross-section with genuinely simulated water: every chamber fills by conservation of volume through the paddle gear you crank, and a narrowboat floats only as high as the water you put under her. Twelve days carry you from a single lock to a staircase pair sharing one gate, then to side ponds that recycle half a lockful through a drought. Hang a stern on the cill or drain a pound and you will know it. Water is a budget; the flight is a machine.