How much time did it take to deploy Crabster each day by putting the robot into the water?

It took 5 minutes to deploy Crabster into water and another 10 minutes to touch bottom 45 meters below surface.

Were there any difficulties in the mothership putting Crabster into the water with its crane and retrieving Crabster from the water? And did Crabster walk and operate well underwater?

We used our own LARS(launch and recovery system) consisting of crane and cable winch. It was the first use of our LARS designed for Crabster. The LARS worked well. During the weather was good, we have no problem with mothership and all the launch and recovery process was done perfectly. But the ship was too small to work in wavy and windy weather. The ship’s roll motion was too big to launch and retrieve the 700kg-Crabster safely. Crabster walked seabed while taking seafloor images with acoustic camera. Crabster was launched 13 times and stayed in water total 15 hours 36 minutes and worked total 11 hours 21 minutes on seafloor while Crabster remained in Jindo for 20 days.

What parts of the Sewol ferry did Crabster inspect? Were there any areas that Crabster had to avoid because of dangerous conditions or other factors?

Crabster was deployed 70 meters away from Sewol. Crabster could see the contour of bow master and upper cabin of Sewol. We wanted to go more close to Sewol but we could not have permission due to the safety of divers. We were very cautious so that Crabster’s tether cable was not entangled to the anchor line of barge. If we could attach our ship to the large barge, we would get more information about Sewol and her surroundings.

What were the most crucial instruments that Crabster used during its deployment at the ferry site? What kind of information did Crabster collect or find during the operation?

Most crucial tool of Crabster in the site was acoustic instrument on the six-legged platform. We could see nothing with ten optical cameras on Crabster. We got acoustic images of sunken Sewol from scanning sonar. We got acoustic images of seabed from acoustic camera. The six-legged Crabster worked well as a stable moving station for the acoustic instrument in tidal current. The Sewol ferry was slanted 90 degrees to port side. The seabed was composed of mud, stones and small pieces of shell. Crabster also acquired depth, altitude, conductivity, temperature. Attitude of body, all joint angles and electric current of six legs were also monitored and recorded in surface control room.

Can you describe the challenging water conditions that Crabster had to navigate? For example, how fast were the currents you had to deal with? How deep was the water? How was the visibility underwater?

The water depth was about 45 meters, visibility was less than 20 centimeters and water temperature was 11~12 degrees C. The maximum current is more than 8 knots at the area but when we were there, the tidal current was less than 3 knots. Sometimes tough wave and wind bother us. The Crabster had no problem to work in those conditions, but Crabster cannot overcome its mother ship. Our ship was too small to keep her position in those current, wind and wave conditions. So we wanted to attach our ship to the large rescue barge firmly moored with four anchors. But we could not have permission.

What were the main goals in using Crabster during the search and salvage operation? What was Crabster's main role in helping assess the ferry's condition or helping to search for people inside?

The Sewol sank at 45m water depth and the water was very turbid. It was dangerous for human divers to search the seafloor. I thought we could inspect the hull of sunken ferry and debris around her using Crabster’s acoustic instrument. And the information would be helpful for the planning of rescue and searching activity. When we reached the ferry site with Crabster system, the divers were going into the sunken ferry continuously for rescue. The highest priority was on the rescue activity by divers and all other team was restricted to approach to the rescue barge. Since Crabster is not able to go into sunken ferry, we also had to wait for approaching permission keeping apart from the rescue barge.

Did you and your colleagues volunteer Crabster to help out at the ferry site? Or did government officials request your help?

When I knew the rescue team had serious difficulties due to the high current and turbid water at the accident area. I called Dr. Suh direct general of KRISO and talked about Crabster’s functions and possibilities for the helping of rescue. Task force team of my institute reviewed underwater robots made in KRISO and agreed to send Crabster to the area. The decision was not easy because Crabster was still under development and the performance was not fully verified. Two days later, government requested our help for surveying of sunken Sewol. We moved the Crabster system from Namyangju to Jindo next day, 21 April.