This study is intended to provide navigator with specific information necessary to assist in the avoidance of collision and in operation of ships to evaluate the maneuverability of research vessel Jera. Authors carried out full-scale sea trials for turning test, zig-zag test, and spiral test at actual sea-going condition, which were performed on starboard and port sides with 10-20 rudder angle at service speed of 10 knots. The turning circle was much different at both of the turning of port and starboard which was longer at the starboard than at the port. In the zig-zag test results, the port and starboard was 10˚ the first and second overshoot angles were 6.0˚, 5.8˚ and 6.3˚ , 7.1˚ respectively and the first overshoot angles were 16.4˚ , 17.6˚ when using 20˚ . Her maneuverability index T and K can be easily determined by using an analogue computer with the data obtained from the zig-zag tests where K is a constant representing the turning ability and T is a constant representing her quick response. In the zig-zag tests under 10˚ or 20˚ at rudder angle, the value K is 0.149. 0.123 sec- and T is 11.853 and 6.193 sec and angular velocity is 0.937˚ /sec and 1.636˚ /sec. In the spiral test, the loop width was unstable at +0.51˚ and -1.19˚ around the midship of rudder, but the tangent line at 0˚ was close to vertical. From the sea trial results, we found that she did comply with the present criterion in the standards of maneuverability of IMO.