"I have been doing this for nearly 20 years so I have a seen a few objects on the bottom, but nothing like this," said Lindberg. "We had been out for nine days and we were quite tired and we were on our way home, but we made a final run with a sonar fish and suddenly this thing turned up," he continued.Using side-scan sonar, the team found a 60-meter diameter cylinder-shaped object, with a rigid tail 400 meters long. The imaging technique involves pulling a sonar "towfish" -- that essentially looks sideways underwater - behind a boat, where it creates sound echoes to map the sea floor below. On another pass over the object, the sonar showed a second disc-like shape 200 meters away.