Hydrodynamic appraisal of hard chine–spray rail configurations for performance optimization of a high-speed monohull craft across turbulent planing regime

Reduction of hydrodynamic resistance and enhancement of longitudinal stability are fundamental to modern high-speed craft design, as they directly contribute to lower fuel consumption, reduced emissions, and safer operation at elevated speeds. This study numerically investigates the effects of different hard chine–spray rail geometries on the calm-water hydrodynamic performance of a planing cougar hull. Eight distinct configurations, including full-chine and one-third-chine widths arranged continuously along the hull length, are examined. Simulations are conducted over a Froude number range of 0.85–1.71 using the Reynolds-averaged Navier–Stokes equations with the k–ε turbulence model in Star-CCM+ software. A mesh sensitivity analysis is performed, and the bare hull results are validated against experimental measurements, showing good agreement. The results show that at low speeds, prior to the planing regime, the addition of hard chine–spray rails increases total resistance due to insufficient dynamic lift. As speed increases and the hull transitions into the turbulent planing regime, the rails reduce trim and increase rise-up, leading to improved hydrodynamic performance. For Froude numbers Fr ≥ 1.07, several configurations reduce total resistance by up to 6.17% compared to the bare hull, accompanied by trim reductions of up to 8.79% and a delayed onset of porpoising. Full-chine configurations demonstrate greater effectiveness in reducing drag and improving longitudinal balance, whereas one-third-chine arrangements perform better in controlling side spray, lowering rooster-tail height, and limiting the extent of near-hull turbulent regions.