Session: 06-05-03 Marine Hydrodynamics - III

Submission Number: 180148

Investigation of Zero-Speed Maneuvering With VecTwin Rudders, Propeller, and Bow Thruster in Shallow and Confined Waters Using CFD Simulations 

Berthing and unberthing have been among the most demanding maneuvers in ship operations, as they have required precise control of forces and moments at very low or zero forward speeds, often in shallow and confined waterways. Under these conditions, without reversing the propeller, control authority has had to be achieved through systems such as VecTwin rudders and bow thrusters. Conventional maneuvering models, including the widely used Maneuvering Modeling Group (MMG) framework, have not been well suited for these situations because they have relied on hydrodynamic derivatives obtained at finite forward speeds and have not been able to fully capture the nonlinear interactions between rudder, propeller, thruster, and hull at zero speed. This has created a clear necessity for a systematic methodology to obtain corrected or additional hydrodynamic derivatives that have represented ship controllability during berthing and unberthing.

This study has focused on a model cement carrier equipped with a VecTwin rudder system, consisting of two independently actuated rudders located behind a single propeller. This system has facilitated large rudder angles, which have enhanced yawing ability without reversing the main propeller. In addition, a tunnel-type bow thruster has been included to represent realistic berthing scenarios where combined rudder and thruster inputs have been applied to achieve precise positioning. A series of steady-state Reynolds-Averaged Navier–Stokes (RANS) CFD simulations has been performed at zero forward speed. The investigation has covered shallow-water conditions with different depth-to-draft ratios, as well as proximity to a vertical bank, to capture the influence of confinement on the generated forces and moments. The CFD computations have included a baseline straight-ahead case, small-angle rudder deflections for local linearization, hover and crabbing cases for maximum lateral authority, and astern-mode cases. For these conditions, a wide range of rudder angles, including large deflections up to ±75° and ±105°, has been considered to capture realistic steering behavior. Additional simulations have combined rudder deflections with varying bow thruster thrust levels to investigate thruster–hull interference and rudder–thruster–propeller coupling effects. A grid independence study has been performed to verify numerical accuracy, and results have been presented in terms of non-dimensional force and moment coefficients.

The CFD results have provided a clearer understanding of the hydrodynamic behavior of VecTwin rudders and thruster arrangements at zero speed. Large rudder deflections have been shown to generate significant lateral forces suitable for crabbing, while opposing rudder angles have enhanced yawing ability, both of which have been essential for low-speed maneuvering near quay walls. The bow thruster has contributed additional lateral control, though its effectiveness has been influenced by hull interactions. These nonlinear effects, which have been inadequately represented by empirical methods, have been systematically quantified and translated into corrected and supplementary MMG components, including bias terms due to bank and shallow-water effects and control-effectiveness coefficients for rudder and thruster actions. The proposed extensions have enabled more realistic simulation of berthing and unberthing maneuvers, complementing unsteady CFD or extensive model testing. Although future experimental validation is needed, the study has established steady-state CFD as a practical framework for extending maneuvering models to the low-speed, confined-water regime, offering both operational guidance and a pathway toward improved simulation and autonomous control in port environments.

Presenting Author: Nusrat Omar The University of Osaka

Presenting Author Biography: Nusrat Omar is pursuing her doctoral degree in the Department of Naval Architecture and Ocean Engineering at Osaka University, Japan. Besides academia, she worked in the field of ship design, gaining practical experience in naval architecture and marine systems. Her research background has been centered on computational fluid dynamics (CFD) since her undergraduate studies. Currently, her research focuses on CFD-based investigation of ship hydrodynamics and maneuvering.

Authors:

Nusrat Omar The University of Osaka
Atsuo Maki The University of Osaka
Kazuyoshi Hosogaya Japan Hamworthy & Co., Ltd.
Masakazu Omote Japan Hamworthy & Co., Ltd.