Improvement of transverse and course-keeping stability of a water-jet propelled planing vessel

Abstract

The running attitudes of planing vessels are dramatically changed while planing, and dynamic unstable phenomena often occur, in particular, at high speed. Therefore, planing hull forms should be designed in consideration of their hydrodynamic characteristics and stabilities. In this study, calm water performance and stability of a 3 ton class water-jet propelled planing vessel are investigated through towing tank model tests and full scale trials. Towing tank tests are performed for a 1/6.5 scale model ship without water-jet propulsion, in order to predict the resistance of a full scale ship. The effectiveness of trim tabs is also investigated by model tests with several trim tabs. Full scale trials are performed with a ship with a water-jet propulsion system, a 315 HP engine, and various measurement systems such as gyro, RTK-DGPS. The ship shows large running trims at around 15 knots, and loses transverse stability at speeds higher than 30 knots. Roll and yaw instabilities at high speeds can be improved by increasing the metacentric height (GM). Trim tabs have an effect on reducing the resistance at speeds lower than 20 knots by reducing running trims greatly, but it rather increases the resistance of the ship at higher speeds where the running trims are not so large. When the trim tab angle is large (10 degree), the running trims are less than 2 degree at above 25 knots. In that case, the ship loses course-keeping ic characteristics and stabilities. In this study, calm water performance and stability of a 3 ton class water-jet propelled planing vessel are investigated through towing tank model tests and full scale trials. Towing tank tests are performed for a 1/6.5 scale model ship without water-jet propulsion, in order to predict the resistance of a full scale ship. The effectiveness of trim tabs is also investigated by model tests with several trim tabs. Full scale trials are performed with a ship with a water-jet propulsion system, a 315 HP engine, and various measurement systems such as gyro, RTK-DGPS. The ship shows large running trims at around 15 knots, and loses transverse stability at speeds higher than 30 knots. Roll and yaw instabilities at high speeds can be improved by increasing the metacentric height (GM). Trim tabs have an effect on reducing the resistance at speeds lower than 20 knots by reducing running trims greatly, but it rather increases the resistance of the ship at higher speeds where the running trims are not so large. When the trim tab angle is large (10 degree), the running trims are less than 2 degree at above 25 knots. In that case, the ship loses course-keeping