“I noticed you were riding high in the water.” He computed the fee, with a steep kicker for moving up in line. “Your account will be charged accordingly.” Then he turned to the pilot. “The Portobelo is cleared to proceed.” He left the bridge and reboarded the pilot boat, which whisked him to the next ship waiting in line.

The pilot sailed the Portobelo down a long channel to the Gatun Locks, the canal’s Atlantic entry point. The locks consisted of a parallel set of three huge sequential chambers, which enabled southbound vessels to be lifted eighty-five feet above sea level to begin crossing the isthmus.

The Panama Canal itself was built like a liquid wedding cake. Its highest point was at its center, the large, man-made reservoir of Gatun Lake. The lake cascaded down three levels at either end. Due to a geographic quirk, the canal’s fresh water flowed to the Atlantic Ocean in the north and to the Pacific in the south. The elevated lake allowed for gravity to fill and drain the locks, raising or lowering ships, depending on their direction of travel.

But the Panama Canal was an uneven wedding cake, due to a separation between locks on the Pacific side. While the three chambers of the Atlantic’s Gatun were sequential, the Pacific’s were far apart, with a single-chamber lock called Pedro Miguel at the lake and a dual-chamber lock called Miraflores a mile beyond. It took a typical ship about eight hours to complete the fifty-mile journey from ocean to ocean.

The pilot inched the Portobelo close to the first chamber at Gatun, stopping just short of its huge open doors, which were called gates. Messenger lines attached to steel tow cables were hoisted aboard and secured, their opposite ends attached to tiny locomotives, called mules, which ran along the lock’s edge. Under the pilot’s guidance, the mules gently towed the freighter into the chamber and held it in place as the gates astern were closed. Once sealed, additional water was released into the mammoth chamber until the ship had been raised nearly thirty feet.

Armed guards, not usually seen around the locks, patrolled the area, giving the ship a careful once-over. When the water level matched the next chamber’s, the front gates were opened and the ship was pulled forward by the mules. The process was repeated twice more, until the Portobelo motored out of the last chamber and into Gatun Lake—eighty-five feet higher than when she started. Clearing the locks, the pilot ordered the helm to increase speed.

“Helm, belay that order,” the captain said. “All stop.”

The pilot’s face turned red. “I command the vessel through the canal!” His demeanor softened when he detected another presence on the bridge. He turned to find Pablo approaching him. “Pablo! I thought this tub was eerily familiar to the old Salzburg. When did you boys get into the container business?”