Numerical Investigation of the Effect of Spray Rail Designs on the Slamming Behaviour of Planing Hulls

Slamming loads represent a major design and operational challenge for planing hulls due to their influence on structural integrity and crew comfort. Spray rails, mounted along the hull bottom, offer benefits such as deflecting spray, enhancing hydrodynamic lift, and reducing drag by limiting the wetted surface area. However, their configuration also modifies the slamming response of the hull during water impact. This study numerically investigates the effect of three representative spray-rail geometries on the slamming behaviour of a planing hull using Computational Fluid Dynamics (CFD). Water-entry simulations of a free-falling wedge-shaped hull section are performed by solving the Unsteady Reynolds Averaged Navier Stokes (URANS) equations with the SST k-ω turbulence model. An overset grid framework is applied for mesh motion, coupled with the Volume of Fluid (VOF) method to resolve the transient air–water interface. Results show that spray rails redirect the incoming flow, reducing peak pressures at regions downstream of the rails while intensifying local pressures near the keel. Dynamic response analysis indicates that while the bare hull exhibits a single acceleration peak, the inclusion of rails introduces multiple peaks corresponding to successive rail–spray interactions. Among the tested geometries, Shallow triangular rails caused smaller increases in pressure and acceleration compared to steeper designs, which led to greater load amplification. This study demonstrates how variations in spray-rail geometry influence transient slamming loads, thereby extending existing water-entry research beyond bare-hull conditions and providing practical insight for more reliable hull strength assessment and design.