High speed sea lift (HSSL) is an important area of interest for the US Navy. Computational tools are needed to predict the hydrodynamics of these multihull configurations for their proper design and analysis in many areas including resistance and powering, motions and habitability, loads in service and maneuverability. To address these issues requires a hierarchy of computational and experimental capabilities. Described here are efforts underway to use unsteady Reynolds averaged Navier-Stokes (URANS) solvers to answer some of these needs. Specifically, computations are demonstrated with CFDSHIP-Iowa to predict relevant HSSL catamaran and trimaran configurations under a variety of operating conditions in both calm water and with waves. Many of these predictions, particularly those representing behavior in various sea states, are very computationally intensive and thus require high performance computing resources. The predictions demonstrated here are paving the way for a computational capability to aid in the design for a new generation of naval ships