Numerical Investigation of Longitudinal Motion and Vertical Acceleration of SWATH and SLICE Vessels with Varying Strut Angles in Regular Waves

When designing small-waterplane-area twin-hull (SWATH) vessels, the main objective has been to maintain speed in rough seas while simultaneously providing adequate performance in head waves. Reduced motion and speed loss can be achieved for these vessels in stormy seas by minimising the draft and consequently reducing the wave-making resistance. One of the challenges faced in the design of SWATH vessels is that as the speed increases, the pressure variations around the hull can induce changes in trim, leading to longitudinal instability. Various solutions have been proposed to improve the heave and pitch motions of SWATH vessels and delay the onset of longitudinal instability, one of which involves generating and modifying the hull form. In this study, a reference hull form for a SWATH vessel is selected. By converting the twin-hull configuration to a four-sub-hull configuration and adjusting the strut angles, a new type of reference hull form can be obtained. Consequently, the SWATH vessel is transformed into a four-sub-hull vessel or a SLICE vessel with the same beam, displacement volume, and strut inclination. A numerical analysis of the heave and pitch motions of this vessel is conducted using StarCCM+ software, and the results are compared with those for the original SWATH vessel. The hydrodynamic analysis and investigation include the response amplitude operator (RAO) of the heave and pitch motions and vertical acceleration of the SWATH and SLICE vessel hulls in regular head waves, and are conducted using the finite volume method. The numerical results for the vessel motion are validated by comparison with experimental data in the literature. The findings indicate that the heave and pitch motions and the vertical acceleration of the centre of gravity for the new vessel are reduced compared to the reference vessel (except at certain frequencies). The proposed SLICE vessel with inclined struts can therefore considered a suitable choice for seakeeping performance under various sea conditions, due to the significant reductions in vertical acceleration and motion amplitude.