Tugs have a simple hull form and good maneuverability. This paper works on the hydrodynamic performance of an ASD harbor tug with a skeg and bilge keels. Virtual oblique towing tests (OTT) and circular motion tests (CMT) are conducted via the Reynolds-Averaged Navier-Stokes (RANS) method, to investigate the resistance and moment characteristics. The obtained low-speed body forces and moments of the harbor tug hull provide a basis for the establishment of the maneuverability model and reference for operators to the hydrodynamic performance of the ship.
In the busy harbor areas, tugs are widely used to execute escort, rescue, berthing-assistant and other missions with low-speed steering. The operational demands of the tug inspire the study of maneuverability in terms of safety, effectiveness and operability. It is delicate and indispensable to study the hydrodynamic performance of the tug in certain motions.
Traditionally, experimental and empirical methods are utilized to study the hydrodynamic forces and maneuverability of a ship. Oltmann (Oltmann and Sharma 1984) studied the hydrodynamic characteristics of a single crew tanker and a twin-propeller twin-rudder container ship based on slow-speed constraint model tests, and predicted the forward and backward motion of the ships. The work of Kho King Koh (Koh and Yasukawa 2012), Fitriadhy and Yasukawa (Fitriadhy, Yasukawa et al. 2015) on the tug-towing system and tug-pusher system enables the prediction of the inland tug assistance system. Yoshimura (Yoshimura 1988), Kijima (Kijima, Katsuno et al. 1990), and other scholars summarized universal empirical methods to predict ship maneuverability under different circumstances.
CFD methods are now widely used to study the hydrodynamic performance and flow characteristics of the ship. Zhang (Zhang, Liu et al. 2019). Chen (Chen, Zou et al. 2017) carried out CMT tests to study the forces and moments of the Esso Osaka model with large drift angles. Based on virtual static and dynamic constraint model tests, Benedetto (Piaggio, Viviani et al. 2018, Piaggio, Villa et al. 2020, Piaggio, Villa et al. 2020) investigated the hydrodynamic forces and moments of an escort tug at slow- and high-speed conditions.