When Bong-Huan Jun first saw news of South Korea's Sewol ferry sinking with hundreds of high school students trapped on board, he had stopped by a highway service area on his way to work. But unlike many South Koreans helplessly watching the live broadcast on TV, Jun knew he had something that could help out — an experimental underwater robot named Crabster.
Crabster was designed by Jun and his colleagues at the Korea Research Institute of Ship and Ocean Engineering (KRISO) as a huge, six-legged robotcapable of scuttling along the ocean floor. The robot can withstand strong tidal currents and carries both sonar and acoustic cameras capable of seeing through murky underwater conditions — precisely the conditions divers had to struggle with as they searched the Sewol ferry wreck in the cloudy waters of the Yellow Sea near Jindo Island.
But Crabster had only just begun underwater testing in July 2013 and remained relatively untested. Now it faced one of the most challenging tests for any underwater robotic vehicle during one of South Korea's greatest maritime disasters in its history.
"When I knew the rescue team had serious difficulties due to the high current and turbid water at the accident area, I called Dr. Sanghyun Suh, director general of KRISO and talked about Crabster’s functions and possibilities for helping with the rescue," Jun said. "The task force team of my institute reviewed the underwater robots made in KRISO and agreed to send Crabster to the area."
The Sewol ferry sinking on April 16 had already kicked off a frenzy of rescue operations by ships and divers. But South Korean government officials eventually requested the Crabster team's help on April 20 and allowed the team to move the robot from Namyangju to Jindo Island on April 21.
When Jun and the Crabster team arrived aboard a mothership, they found dozens of ships and a swarm of smaller boats surrounding the main rescue barge anchored near the ferry sinking site. Divers were working with a visibility of less than 20 centimeters at a depth of about 45 meters below the surface. They also had to deal with maximum tidal currents of more than 15 kilometers per hour. (Crabster experienced currents of less than 5 kilometers per hour during its initial deployment.)
"Crabster can stay deeper and longer, and it can see father," Jun explained. "But Crabster cannot go into the ship. We wanted to work together with human divers, but we had no chance to do."