An important aspect of maritime safety is the environmental influence on stability of ships. Heavy accelerations potential capsizing are threats for ships, goods and humans. A factor of ship stability and safety is the sea state interfered from wind and waves. Sea conditions and operational experiences are the base for safe navigation. These parameters can be generated from satellite data (a low frequency) and wave buoy measurements (near the coast). That is why the sea state parameters are mostly not available, unknown or incomplete on high seas. The sea state can be described by a wave spectrum from which the ship's responses can be derived. Different models to describe the wave spectrum (like Pierson-Moskowitz, Bretschneider, JONSWAP, Ochi-Six-Parameter) are provided. The identification of the acting wave spectrum on the ship is important to calculate the ship response. This paper presents a classification heuristic for the use of a suitable wave spectrum for the prevailing sea state. This serves to approximate as closely as possible the true wave spectrum (the ground truth). For this purpose, suitable parameters are defined from the ship motion and weather influences for the determination of limit values as well as for the solution of the spectral equations of idealized spectral families. This serves the purpose of a later applied assistance system. An assistance system improves the risk prediction for navigation in order to avoid roll, container, stability or maneuvering losses.