NAVTEX (Navigational Telex) is an international automated medium frequency direct-printing service for delivery of navigational and meteorological warnings and forecasts, as well as urgent maritime safety information to ships.

Using my FT847 or my SDR to listen on NAVTEX frequencies 490 KHZ, 518 KHZ or 4209.5 KHZ.

Parameters: FSK, 100Bd, Shift 170

A good introduction to NAVTEX DXing found here.

Screenshot shows NAVTEX on 490 KHZ:

Using the SDR and  Frisnit NAVTEX decoder software to receive/decode NAVTEX signals: