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Catching Zzzs

Fresh from refinishing work, the “Z-drive” propulsion units on the underside of the research vessel Knorr are exposed in a Jacksonville, Fla., shipyard. The shrouded drives can turn 360 degrees, giving the ship a remarkable ability to maneuver and–when combined with a bow thruster–to ‘hold station,’ or stay in one place, while working at sea. (Photo by James Broda, Woods Hole Oceanographic Institution)