The recent development of CFDShip-Iowa Version 6, a high-performance, high-fidelity Cartesian grid solver for computational ship hydrodynamics, is presented. First, a wall function approach has been introduced for wall-layer modeling based on the immersed boundary method and the one-equation Spalart-Allmaras turbulence model. Second, in order to develop more advanced wall-layer modeling schemes, an orthogonal curvilinear grid solver based on the Cartesian grid solver has been implemented and tested. Third, a coupled level set volume-of-fluid method has been developed to substantially improve the volume conservation properties of the interface tracking/ capturing schemes. In addition, fluid-structure interactions for ship motions in the framework of current Cartesian grid solver are also discussed. Finally, domain decomposition using MPI in all three directions has been included, parallel I/O becomes fully functional, and a new high-performance Poisson solver has been implemented. A series of cases ranging from the NACA0024 hydrofoil, Wigley hull, surface combatant DTMB model 5512, bow waves by a wedge, and surface-piercing circular cylinder, etc., have been carried out to validate the accuracy and demonstrate the scalability of the current method. Results including wave field patterns, velocity fields are successfully compared with experimental data and other computational results.