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Jon Burgess (left) and Ben Wigham (right) take the pinger off the dredge wire. The pinger emits a 12 kiloHertz “ping” which bounces off the seafloor and comes back to the ship’s recorders in the Main Lab. The recorder shows the distance between the pinger and the seafloor; that tells us how high above the bottom we are. We usually put the pinger about 150 meters above the dredge. When the recorder shows that the pinger is about 50 meters above the bottom, we know we have the dredge and about 100 meters of the dredging wire on the bottom. As the ship moves forward slowly, the dredge is pulled along the bottom to scoop up rocks.

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