Canal authorities said Saturday that dredgers had managed to dig out the rear of the ship Friday night, freeing its rudder, and that by Saturday afternoon, they had dredged 18 meters down into the canal's eastern bank, where the ship’s bow was stuck solid. But after a salvage team failed once more to dislodge the four-football-field-long leviathan from the sand bank where it ran aground Tuesday, blocking all shipping traffic through the canal, global supply chains churned closer to a full-blown crisis.