Science: Probing The Monitor with a Deep Drone

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It has been 14 years since marine archaeologists rediscovered the U.S.S. Monitor, the Civil War ironclad that sank in a storm near Cape Hatteras, N.C., ten months after the historic 1862 standoff with its Confederate counterpart, the C.S.S. Virginia.* Since then more than 100 artifacts have been recovered from the wreck, including wine bottles and a 1,300-lb. anchor. Despite the Monitor's designation in March as the country's first undersea National Historic Landmark, scientists and Government officials have been unable to decide whether the ship itself can be salvaged. Last week, after a 14-day expedition led by the National Oceanic and Atmospheric Administration, they had a preliminary answer. Said NOAA Project Coordinator Ed Miller: "It is doubtful we will ever bring up the entire ship because of the high cost and risk of breaking it apart."

The 172-ft. Monitor lies bottom up some 220 ft. below the surface, balanced on its cylindrical "cheesebox" turret. Since divers cannot work easily at that depth, scientists knew only that the ship's metal hull was corroded, but they did not know how badly. Indeed, the new data gathered on the Monitor < represent a significant advance in undersea research. "This is a prototype for marine archaeology," says NOAA Spokesman Dane Kanop. "We are writing the book."

The showpiece of the operation was the Navy's Deep Drone, a sophisticated undersea robot. The drone was connected to the U.S. Navy tug Apache by an umbilical cord that transmitted commands and returned data from an array of cameras and sensors to shipboard computers and monitors. An acoustical locating system, accurate to within 20 in., will guide scientists in assembling a photomosaic of the more than 2,000 high-resolution still photographs the drone has taken of the ship's hull. In addition, a sonar scan will be used to make a false-color three-dimensional computer map of the Monitor.

To learn how fast sections of the hull are corroding, the drone poked "stab sensors" through encrusted sea life and rust and measured the electromagnetic field at the ship's surface. Reason: the Monitor's iron and steel combine with salt water to form a weak natural battery. The resulting electric current peels electrons from the hull, making it easier for oxygen atoms to attach themselves; oxidation, or rusting, ensues. To protect the Monitor while officials decide what to do, scientists may attach "sacrificial anodes" of zinc to the hull to divert the corrosion process away from the aging metal.

The final decision on the Monitor will have to await complete analysis of the drone's findings, but there may not be much time. Says Project Archaeologist Barto Arnold: "The wreck is in very bad shape; artifacts are spilling out and being washed away by the current." No more artifacts of the ship will be raised until tricky questions of recovery, restoration and eventual display are worked out. Says Miller: "We have learned with other shipwrecks that premature recovery leads to certain destruction."

FOOTNOTE: *The wooden frigate Merrimack was fitted with iron plates and rechristened Virginia.