Three Sheets to the WindWhy loose ropes made sailors look drunk.

From the show

History of Phrases

In the age of sail, a "sheet" was not the canvas sail itself, but the rope used to secure the sail's bottom corner to the ship. If a sheet came loose, or was "to the wind," the sail would flap uncontrollably, causing the vessel to stagger and wobble. A ship with three loose sheets was completely out of control, mimicking the gait of a heavily intoxicated sailor.