Have a look into the manual - "chart sources". A lot of information.
you get free charts for the (commercially used) Inland Waterways (Binnenwasserstrassen) and a good part of them you access via the integrated Chartdownloader.
OpenSeaMap is using coastlines from the OpenStreetMap project
, lighthouses and markers from public data bases and lack in general soundings.
So not really helpful for navigation
For a good part of the European waters you get non free, but quite inexpensive and up-to-date vector charts from the oeSENC project