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 robot capable 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 farther," Jun explained. "But Crabster cannot go into the ship. We wanted to work together with human divers, but we had no chance to do."
The South Korean Coast Guard refused to allow the relatively untested Crabster to work directly with human divers at the ferry wreck, but it eventually gave the robot's team one and a half hours to survey the sunken ferry from a distance of 70 meters. Jun and his colleagues had originally wanted permission to tie their ship to the large rescue barge that was firmly moored to the seafloor with four anchors, so that they could steady their smaller ship against the wind and waves while deploying Crabster. But they made the best of their circumstances during the 20 days they spent at Jindo Island.
Strong waves and wind created a rolling motion in the mothership that made it difficult to launch or retrieve the 700-kilogram Crabster during bad weather days. Such bad weather meant the team spent 15 of their 20 days of deployment stuck in port waiting for conditions to improve.
During the initial survey, the mothership drifted too close to the rescue barge and required the help of a nearby tugboat to back out again. A lack of space aboard the mothership also meant the team went without sleep for the first three days and two nights, until they retired to the nearby Pengmok Harbor to rest and wait for additional windows of opportunity.
Still, Jun and his colleagues ended up launching the robot 13 times, allowing the robot to spend 15 hours and 36 minutes in the water. After an initial two-day survey, the team spent an additional three days surveying the sunken Sewol ferry from distances of 500 meters to 1 kilometer.
Despite its baptism by fire, the Crabster robot worked perfectly as it walked across the seabed containing mud, stones, and small pieces of shell. The robot successfully used its acoustic camera and sonar to capture images of the seafloor, providing a stable platform for surveying the ferry wreck despite the tidal currents.
The Crabster team eventually returned to their home base in Namyangju on May 20 and unloaded the robot. There they joined their fellow citizens in confronting the grim death toll from the Sewol ferry disaster—at least 286 dead, most of them students on a school trip. South Korean president Park Geun-hye ordered the dismantling and reorganization of the country's coast guard on May 19 as part of several reforms in the wake of the tragedy, according to BBC News.
Jun believes that Crabster needs additional experience in the water before the South Korean government will fully trust the robot's capabilities—he had expected the robot to be used even more than what the coast guard had allowed. But he and his colleagues hope to build upon their experience to be better prepared for any future rescue missions that may come up.
"I think the next Crabster should be a powerful hydraulic-powered one having enough power to break the doors and windows of [ship] cabins," Jun said. "Then the robot will be able to install guide ropes and make routes to inside the ferry for divers at the initial rescue stage."