Hydrostatic Stiffness Data Hydrostatic stiffness matrix and reference position for stiffness force, i.e. the global position where stiffness force is zero. For floating vessels the gravity and buoyancy forces are normally modeled by use of the hydrostatic stiffness matrix, where the reference point for stiffness is taken as the position where buoyancy and weight are in equilibrium. Damping Matrix Small Body Hydrodynamic Data