Multi-legged ROV Crabster and an acoustic camera for survey of underwater cultural heritages

In west coast of Korea peninsula, there are some offshore sites where ancient sunken shipwrecks have been discovered. These ships are supposed to carry an amount of artifacts what show lifestyle and culture of the day. In these areas, however, because of fast ocean currents and low visibility, underwater survey and excavation by divers are strictly restricted. Especially, optical cameras and human's visual inspection become defective. To overcome these conditions, use of unmanned underwater vehicles such like a ROV(Remotely Operated Vehicle) which is equipped with acoustic imaging devices has been raised. This paper describes preliminary performance experiments for survey of underwater cultural heritages using a ROV whose name is Crabster driven by six artificial legs with a high-resolution acoustic camera in sea. The Crabster uses the six articulated legs actuated by BLDC motors as its thrusters. Therefore, it moves on the sea floor without disturbances by propellers which are widely used as thrusters of any other general ROVs. In addition, The robot is expected to minimize shadow areas of acoustic imaging sensors by controlling its body posture precisely using the legs. In this paper, we introduce operations of Crabster and the acoustic imaging devices when we conducted from April to May in 2015. Using acoustic imaging devices, we could find dispersed potteries and iron caldrons. Mosaicked image to show surround of the robot is also included.