Comparison of Slamming Force Calculations for a Semi-Displacement Vessel

Growing interest in midsize semi-displacement vessels for crewed or autonomous operations necessitates accurate slamming/whipping load predictions-key design drivers for larger, faster vessels. While hydro-elastic experiment and Computational Fluid Dynamics (CFD) are often cost-prohibitive, potential flow codes offer a quicker alternative. However, their reliability is hampered by a lack of validation against comprehensive hydro-elastic model test data. Addressing this gap, the US Naval Academy performed hydro-elastic experiment on a 154 ft vessel. This paper presents a qualitative comparison of experimental data with simulations from the Large Amplitude Motion Program (LAMP). The comparison focuses on all four impact force calculation methods within LAMP, aiming to enhance predictive accuracy for these critical loads. INTRODUCTION The maritime industry exhibits a growing interest in designing increasingly faster and larger vessels for crewed or autonomous operations. As a vessel's speed increases, dynamic lift forces are generated on the hull, supporting a portion of its weight and causing the vessel to enter the semi-displacement speed regime. While structural optimization is a universal design goal, reducing structural weight is particularly critical for semi-displacement vessels to achieve desired speeds, increase payload capacity, or reduce greenhouse gas emissions. Consequently, accurate prediction of hydrodynamic design loads is fundamental to structural optimization. Research by Judge and Ibrahim (2025), among others (e.g., Sheinberg et al., 2011), has established that critical nonlinear slamming and whipping load effects warrant careful consideration during the design of semi-displacement vessels. These effects are typically categorized by their impact on either the tertiary structure (local elements like plates and stiffeners) or the primary structure (contributing to global hull girder strength). For small high-speed vessels, design strength is often dictated by local slamming pressures on the tertiary structure. As the size of high-speed vessels increases, global hull girder strength becomes increasingly critical. Notably, the global vertical bending moment (VBM) scales with the square of the vessel's length (IACS, 2020), meaning even modest increases in length can significantly increase the global hull girder VBM. For this reason, the American Bureau of Shipping (ABS) mandates global hull girder strength compliance for high-speed naval vessels exceeding 24 m (79 ft) in length (ABS-LHSNV, 2024), whereas Det Norske Veritas (DNV) applies this requirement to vessels over 50 m (164 ft) (DNV, 2015). Although addressing local slamming effects is important, local reinforcements can often be added relatively easily to rectify local structural failures during a vessel's service life. Conversely, modifying the primary hull structure post-construction to compensate for underpredicted global slamming loads is significantly more challenging and costly. Consequently, for larger vessels, the impact of slamming and whipping on longitudinal hull girder strength is a more critical design consideration.