Hydrostatic Stiffness Matrix Hydrostatic Stiffness Matrix has been deprecated and replaced by Linear Hydrostatics, which includes submerged volume and center of buoyancy explicitly, making it easier to use with models where weight and buoyancy are not in balance. To replace Hydrostatic Stiffness Matrix with Linear Hydrostatics, you can: Re-import hydrostatic data from a SIF file, or, Create a new Linear Hydrostatics model and provide the necessary input manually. 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. Linear Hydrostatics Small Body Hydrodynamic Data