Max Headroom: big container ships are beginning to encounter height restrictions under bridges. (Special report: the top 50 container lines).(Bayonne, New Jersey and other ports)(Brief Article)(Statistical Data Included)

When ports and shipping companies discuss draft restrictions, they're usually referring to the depth of channels and berths. But as a recent incident in New York harbor showed, "air draft" also can be an important consideration.

When a China Shipping vessel, the Tianjin, arrived in New York harbor bound for the port's main container terminal complex in Port Elizabeth. N.J., the docking pilot decided the ship would exceed the "air draft," or available clearance, under the Bayonne Bridge.

Instead of discharging cargo at its regular berth at Maher Terminals in Elizabeth, N.J., the ship had to discharge its load of about 1,000 containers at Global Marine Terminal on the Hudson River in Jersey City.

Dennis Wheeler, vice president of the Sandy Hook Pilots, said the incident was unusual but not unprecedented. He noted that clearance under the Bayonne Bridge has been …