IHO S-104

IHO S-104 is the Water Level Information for Surface Navigation product specification in the S-100 family, delivering predicted and real-time tidal height as a time-varying surface an ECDIS can apply directly. Instead of an officer reading tide tables and interpolating between standard ports, an S-100-capable ECDIS ingests S-104 to show the height of tide at the ship’s position and time. Combined with S-102 gridded bathymetry, it computes a live under-keel clearance and a safe tidal window across a shallow bar. S-104 is one of the data layers that makes S-100 ECDIS more than a chart display: it turns the passage plan into a depth-aware, time-aware tool.