Hydrodynamic Performance of High-Speed Craft: A CFD Study on Spray Rails

In high-speed crafts, whisker spray increases viscous resistance by enlarging the wetted surface near the stagnation line. Spray rails (SRs) mitigate this issue by redirecting water flow, reducing the wetted surface, and lowering overall resistance. This study investigates the effect of SRs on the hydrodynamic performance of the C1 hull of Naples Systematic Series (NSS), focusing on the systematic variations in size, number, and placement. Numerical simulations, validated with towing tank results, were conducted using STAR CCM+ 2306. Mesh independence analysis was also performed to optimize computational efficiency. Key findings highlight the critical role of SR design in performance optimization. Wider SRs (e.g., three per side, 0.96% LWL) reduced resistance by up to 8.5% at high speeds (Fr∇= 3.26), but slightly increased the resistance at lower speeds (~2%) due to a larger wetted surface. Narrower SRs (e.g., three per side, 0.48% LWL) achieved resistance reductions of up to 4.6%, while configurations with multiple SRs (e.g., three per side, 0.72% LWL) outperformed single-rail designs by reducing resistance up to 4%. Placement near the chine proved more effective than near the keel, offering a 4% additional reduction in resistance. Additionally, SRs generated lift, raising the hull, and reducing immersion. The study underscores the importance of optimizing SR size, number, and placement to enhance hydrodynamic efficiency, particularly for high-speed operations.