Prepare your charts before departure
Mobile coverage is not guaranteed at sea. Keeping authorised charts in local storage makes them available without a connection, provided your equipment and onboard network are working.
Formats and licences
Check the coverage, currency and licence of each source. Open Marine Charts supports MBTiles and import workflows for raster files and unencrypted S-57; it does not decrypt protected commercial charts.
Have a backup plan
Check your charts and power supply before departure and carry appropriate alternative navigation resources. An application does not replace a proper lookout or navigation procedures.
Prepare the whole passage, not only the departure chart
Mark the intended sailing area, ports and reasonable alternatives. Before departure, open each area on the screen you will use on board and inspect several scales: a loaded overview does not guarantee that approach detail is available. Record the source, date and terms of use, and check applicable notices to mariners.
Test offline operation
With charts imported and the boat in port, temporarily disconnect internet access without switching off the local server network. Reopen the application on another screen, inspect the relevant areas and confirm the charts still load; then restore connectivity. This exposes missing coverage and network dependencies, but does not itself establish that a chart is official, current or suitable for navigation.
Questions to ask about a file
Check who publishes the data, when it was updated and whether its licence permits your intended use. MBTiles describes tile storage, not authority or currency. Open Marine supports MBTiles and certain local imports; it does not decrypt S-63. Keep documentation and alternative resources appropriate to the vessel and passage.