High Speed Craft (HSC) occupants can be exposed to eccentric slam impacts of up to 20 g as a result of hull separation from the water during routine operation, subjecting the occupants to lateral, longitudinal, torsional, and vertical loading. These impacts have been the source of acute and chronic spinal injury for occupants. Development and validation of an accurate mathematical model of HSC suspension seating with the ability to optimize seat design parameters is required for efficient seat analysis, design, and tuning. A Newton-Euler approach was used to develop a general two-degree-of-freedom (DOF) spatial dynamic model of the seat-occupant system to accurately predict the occupant’s vertical response to 6DOF input base motion. The model was validated against uni-directional, single impact experimental data and available 6DOF HSC data and found to adequately predict the occupant’s vertical acceleration when using the stiffness and damping characteristics from component testing of the seat.