S-104 Water Levels

S-104 is the IHO S-100-based product specification for water-level information for surface navigation, encoding predicted and real-time tidal heights and water levels on a time-stepped grid or at stations. Combined with S-102 bathymetry and a vessel’s draft, it lets ECDIS compute dynamic under-keel clearance and tidal windows rather than relying on static charted depths plus separate tide tables. It pairs with S-111 surface currents and S-124 warnings in the e-navigation product set under the S-100 data model.