From Cruising World...
DroidNavtex can decode messages from any SSB, amateur radio, or shortwave receiver. Simply tune into the Navtex frequency (518 kHz or 490 kHz), place your phone or tablet next to the speaker, and receive valuable and current weather information. Special audio filters are embedded in the app making it possible to decode very weak signals.
DriodNavtex is available for $9.99 at Google Play and Amazon Appstore for Android.
Vice Commodore, OCC