The bridges were closed to traffic while the ship approached and passed underneath with its giant cargo.
At the same time, the load is 450 feet wide — nearly half the width of the channel under the Bay Bridge.
"Yes, it will look dramatic, quite startling," Capt. Eric Nielsen, president of the Association of Maryland Pilots, said Tuesday. "Frankly, it would look dramatic if the clearance was 30 feet."
The Maryland Transportation Authority temporarily stopped traffic on the Bay and Key bridges this afternoon. The closures were designed to prevent distracted motorists from slamming on the brakes or running into each other as the giant cranes approached and passed underneath the spans.
The 14-story cranes each weigh 1,550 tons and can reach 22 containers across on a cargo ship. They can lift 187,300 pounds, or more than an empty space shuttle.
The cranes were purchased by Ports America Chesapeake for $40 million as part of a public-private partnership that included dredging Berth 4 at Seagirt Marine Terminal to handle the world's largest ships.
Planning the final 20 miles of the Zhen Hua's voyage began April 14, when the cranes left China.
The Zhen Hua arrived in the Maryland portion of the bay the evening of June 11, just before the tall ships arrived in Baltimore from Norfolk, Va., for Sailabration. The vessel anchored about 11 miles south of the Bay Bridge and began a weeklong series of preparations.
The cranes had traveled 14,000 miles with the booms locked skyward to aid stability, a configuration that would, however, have prevented the ship from getting under the bridges.
So the ship's operators lowered the booms while shifting ballast to maintain balance. In addition, they added water ballast to lower the ship by about two feet.
Other vessels will not be allowed in the shipping channel during the 17-mile trip between the bridges, and law enforcement vessels will provide an escort.