The center span of the Chesapeake Bay Bridge in Maryland towers 186 feet above the nation’s largest estuary. And nearly every inch of that clearance was needed Wednesday for a freighter to deliver four Super-Post-Panamax cranes to the Port of Baltimore.

Funded by Ports America Chesapeake, which operates the Port for the Maryland Port Authority, the 140-foot-tall, 1,550-metric ton Chinese-made cranes are the highest-profile components of  efforts to lure East Coast-bound supersized container ships once the $5 billion expansion of the Panama Canal is completed in early 2015.

Augmenting the recently completed 50-foot deepening at the Port’s Seagirt Marine Terminal’s Berth IV, the cranes’ booms will be able to extend 206 feet—the width of 22 containers, four more than the Port’s seven existing Post-Panamax cranesand lift more than 93 tons. Currently, Virginia International Terminals in Norfolk has the East Coast’s only Super-Post-Panamax capabilities.

But before these lofty plans could be realized, the cranes had to survive the inherent challenges of  a two-month sea journey from China before overcoming…er, “undercoming” their final obstaclesthe Bay Bridge, and the Francis Scott Key/I-695 Bridge at the entrance to Baltimore Harbor.

The passage was an exercise in coordination involving the Coast Guard, the Association of Maryland Pilots, and state transportation agencies, which shut down traffic on the Bay Bridge as the tugboat-guided freighter Zhen Hua 13 gingerly edged closer.

With temperatures nearing 100 degrees, there was concern that the steel suspension bridge’s natural expansion and sagging would offset any advantage gained by arriving at low tide. There was even talk of positioning a crewmember atop the cranes to literally “eyeball” the clearance, as the pilot’s view from the wheelhouse was obscured.

The planning, professionalism, and crossed fingers paid off, as the cranes slipped beneath the Bay Bridge’s steel underside with no more than 10 feet to spare.

Here's a YouTube video of the action, uploaded by the Annapolis Capital.

Two hours later, the squeeze play was repeated at the Key Bridge, this time with only about four feet of breathing room beneath the continuous truss structure.

Finally home in Baltimore, the cranes will be unloaded and assembled with an eye toward being put into service this Fall.

More videos of the cranes’ passage to Baltimore are available at the Baltimore Sun’s website.