The primary function of these data categories is to describe the structure or structures being modeled. This includes the mass and inertia of the structure and its geometry from which the hydrostatic and hydrodynamic properties are calculated.

In addition, the coordinates of all positions referenced in subsequent data categories and the parameters relating to the static environment (e.g. density of water) are input.

These parameters are normally considered to remain constant throughout the analysis of a particular structure. This means that for further program runs these data categories must be removed, as the information will be contained in a backing file and will be read automatically.