Enriches your map with information about sailing routes, navigation lights, nautical danger zones, zones with sailing or docking restrictions, etc. To use, download the respective Nautical maps and enable the "Nautical map" style under "Configure map". 

Further reading at https://osmand.net/docs/user/plugins/nautical-charts .
Turn on to enrich your map with information about sailing routes, navigation lights, danger zones, zones where it is allowed or prohibited to sail or dock, etc. To use download Nautical maps and enable "Nautical map" type in Configure map. 

How to - https://osmand.net/docs/user/plugins/nautical-charts