Getting bigger ships safely under the Don Holt Bridge on Interstate 526 is the aim of new technology that goes on the span next week.

The $40,000 Web-based system provides immediate, current information on bridge clearance.

The “air gap” system, so named because it measures the space between the water’s surface and the bottom of the bridge, is accurate to at least 6 inches, said Rich Bourgerie, an oceanographer with the National Oceanic and Atmospheric Administration.

“Ships are getting taller,” he said.

Bourgerie will be here as part of a NOAA team tasked with getting the new system up and running by May 15.

In addition to safety, the high-tech bridge-clearance monitoring also is good for commerce, he said.

“The large ship companies really don’t want to come up if there is even a slight chance of a bridge collision,” Bourgerie said. About a dozen bridges nationwide have the technology. The Don Holt is believed to be the first span in South Carolina to add the new measure of safety for ships and bridge traffic.

The State Ports Authority is footing the tab for the system.

SPA’s North Charleston Terminal and the Naval Weapons Station Transportation Command have ship traffic under the Don Holt.

The ports authority said in a letter to NOAA that installation of the technology on the Don Holt is absolutely necessary for navigation safety, continued business development and job creation at the Port of Charleston.

Currently, there are five weekly containership services in Charleston that deploy vessels too big to transit the Panama Canal. The biggest ships move through the harbor on the high tide to gain extra draft clearance.

“In addition to requiring additional water depth, these vessels are longer, wider and — in many cases — taller than ships previously calling our port,” Steve Kemp, SPA vice president of terminal operations, said in a letter to the federal agency.

The Don Holt has 31 feet less vertical clearance over the Cooper River than the Arthur Ravenel Jr. Bridge at average high tide, Kemp said.

Along with tides, air temperature can affect bridge clearance. Summer heat causes bridge materials to expand while winter cold shrinks them, Bourgerie said.

“You can have a few feet of difference in some of the colder air,” he said.

The new bridge-clearance data will be available to ships locally through the Internet and by phone. It is part of NOAA’s Physical Oceanographic Real Time System.

The agency’s National Ocean Service notes that more than 95 percent of U.S. international trade moves through the nation’s ports and harbors, with about 50 percent of the goods being hazardous materials

“With increased marine commerce comes increased risks to the coastal environment, making marine navigation safety a serious national concern,” the ocean service says.

Reach Prentiss Findlay at 937-5711