The Lagrangian Differencing Dynamics (LDD) method, which simulates incompressible fluids with a free surface, has been extended to model planing of fast boats on calm water. It accurately handles rigid-body Fluid-Structure Interaction (FSI) through implicit solving of the Navier-Stokes equations and Lagrangian flow of water parcels, with walls represented as freely moving and deforming triangle meshes. The coupling involves direct exchange of fluid forces and wall motion. To validate the method, simulations of a hard-chine planing hull form were performed, comparing the results to experimental data. The resistance force and trim angles were analysed, for beam Froude coefficients Cv 1.4 and 2. The pressure distributions along the hull bottom and wave elevation around the hull were also examined. Due to its meshless Lagrangian nature, setting up a simulation only requires surface representation of the hull while utilizing modern GPUs allows obtaining results within minutes, making it suitable for optimization of planing hull forms.