Efficacy of transverse step distance from transom on hydrodynamics of a single-step planning vessel: An experimental and numerical analysis considering load and longitudinal center of gravity shifts in calm water

The dynamic relationship between loading, longitudinal step distance (LS), and longitudinal center of gravity (LCG) plays a vital role in determining hydrodynamic efficiency of high-speed boats. This research focuses on a 2.5-m model analyzed through both experimental and computational approaches. Experiments cover a velocity range of 1–8 m/s, with Beam Froude numbers (FrB) from 0.45 to 3.6, and test weights of 63 and 76.6 kg, corresponding to load coefficients (CΔ) of 0.5 and 0.61. The LCG positions are precisely adjusted to 32%, 34%, and 36% of the boat's overall length (LOA). In the numerical study, load values are set at 48.824, 63, and 76.6 kg, yielding CΔ values of 0.382, 0.5, and 0.61. The LCGs match the experimental setup, and step distances are defined at 0.6, 0.7, and 0.8 m—equivalent to 24%, 28%, and 32% of the LOA. Simulations employ Star-CCM+ software, using the Finite Volume Method (FVM) for detailed three-dimensional analysis. The SST (Shear-Stress Transport) turbulence model and Volume of Fluid (VOF) approach are applied to simulate turbulent effects and free surface interactions, with Overset mesh method handling motion dynamics. Both experimental and numerical analyses measure trim, rise-up, and drag, while also examining wetted surface areas, pressure patterns, and wake structures. Results show that as the step moves further from the stern and the LCG shifts forward—specifically from 0.85 m to 0.9 m—the trim angle, lift, and drag relative to weight all decrease. A noticeable reduction in rooster tail formation is also observed.