The maximum velocity of the URI-L ROV was measured 2.8kts in the water tank. At the design step, the ROV was expected to run at the velocity of over 3.5 knots with 6 thrusters of 5.5kW each. The resistance and thrust of the ROV at different flow velocity were measured in the circulation water channel to analyze the discrepancy of its maximum velocities. It is confirmed that the thrusters arranged at 45° have a greater thrust attenuation than the thrusters arranged in the forward direction.
The Korea Research Institute of Ships and Ocean engineering (KRISO) has been developing light work ROV as part of underwater construction robot project (Fig. 1). Light work ROV is capable of carrying out various tasks in underwater construction and is compact than other underwater construction robots, and it is designed to be able to reach a maximum speed of 2.5 knots by using 6 horizontal thrusters out of 10 at its own weight of 1.5 tons.
The ROV URI-L under development was able to reach speeds of up to 2.8 knots with its own DVL (Doppler Velocity Logger) record in a threedimensional water tank test of the Underwater robotics Test & Evaluation Center at Pohang. This has exceeded the design speed of 2.5 knots, but lower than the initial design expectations.
The ROV URI-L uses six thrusters arranged horizontally to achieve a forward speed. Four out of six thrusters are placed at an angle of 45° to the center line at the front, rear, left, and right sides of the ROV, and two are placed at the bottom of the stern (parallel to the centerline). Fig. 2 shows the location of the horizontal thrusters. Most of ROVs with open frame take this type arrangement because of better maneuverability and more room for sub systems than inline arrangement of thrusters. The URI-L ROV is 2.3m long, 1.27m wide and 1.3m tall.
In this arrangement, the maximum speed could be 3.5 kts from simple calculation of vector sum of each thrusters as the Eq. 1 where T is the maximum thrust of each propellers.