A variety of robots has been studied and developed for undersea exploration. One of the applications for undersea exploration is mining of undersea resources such as methane hydrate and rare metal by Autonomous Underwater Vehicle (AUV). To extend active duration time of the robot in the sea, a system through which the AUVs recharge autonomously batteries is a key technology. The authors have confirmed in a pool environment the dual-eye visual servoing system made a pole attached to the vehicle dock into a pipe that simulates recharging station, but the abilities have not been verified in real sea environment. The purpose of this paper is to scrutinize the capability that the visual servoing system can conduct docking operation in real sea, which has disadvantage like impurity deducting visible distance comparing a condition in a pool filled with tap water and disturbances made by waves and currents. The docking has been conducted five times and four docking trials have been successfully completed, and all four succeeded docking data have been presented in detail with behavior analyses of the robot in the sea.