A sailing ship is becalmed when in the absence of wind, it sits motionless on the surface of the sea.
First found: 1550, to becalm, to deprive a ship of wind.
“As idle as a painted ship upon a painted ocean” C.S. Forester (1899-1966)
Featured image: from Horatio Hornblower, The Frogs and the Lobsters (1999)