The tools available to engineers have changed radically in the last 15 years or so. In the good old days, even what would now be considered the most basic calculations which could be done in a spreadsheet would take days or weeks by hand using a slide rule, planimeter which measured area, or if you were really lucky, a mechanical integrator. The new work horse tools for the modern naval architect are finite element analysis and computational fluid dynamics code. These allow for calculation of the stress in the structure with much greater accuracy and resolution than traditional calculations, and the flow of water around the vessel to assist in not only calculating power requirements, but the visualising of the flow to assist in placement of spray rails, transom design, location of exhausts and airflow through the superstructure.
Damien Smith Design has a dedicated computational facility with a mini supercomputer cluster optimised for the OpenFOAM CFD package.