The port area is a specific region where the water depth is not so deep, the change of the flow is complex, and the transparency of the seawater is low. In the construction and the management of port facilities, it is very important to observe the situation under the water. In this paper, the "Autonomous Towed Vehicle" used in three navigation modes (towed, autonomous and "kite") is proposed as an underwater observation system in the fast current area according to the level of turbulence. First of all, necessary functions were examined for the given missions as an underwater observation system. At the next step, the stability of this system was verified by the simulation concerning the basic motion based on the supposed physical values. As a result, it was clarified that increase of the added weight and the area of the forewings were necessary to ensure the stability of this system which had the special feature as the towed vehicle. It was also shown that not only heave and pitch control by the parallel-motion of the forewings but also roll control by the differential-motion of the forewings were necessary. Furthermore, the hydrodynamic coefficients were obtained by the 1/2 model towing tank test. The observation system developed in this research can be applied to an environment monitoring system in similar conditions, and can be used for various investigations in port area.
