Maritime Safety Information (MSI) and NAVTEX/SafetyNET reception
MSI sources
MSI includes navigational warnings, meteorological warnings and forecasts, SAR information, piracy warnings, and other urgent safety information. It is broadcast through NAVTEX, Inmarsat EGC SafetyNET, and HF NBDP. NAVAREA and METAREA coordinators issue the content. NAVTEX is a localized MF service; SafetyNET is a satellite EGC service with fixed-area addressing. A vessel may use either or both according to its sea area and carriage requirements.
NAVTEX format
International NAVTEX uses 518 kHz in English, with national transmissions on 490 kHz and some tropical broadcasts on 4209.5 kHz. The signal is F1B, 100 baud, 170 Hz shift, with forward error correction. A message begins ZCZC, followed by B1 station identifier, B2 message type, B3B4 serial number, then the text, and ends NNNN. The receiver is programmed with station and message-type selections. International 518 kHz messages should be received in English.
Worked example
A NAVTEX printout begins ZCZC FA01, followed by a navigational warning, and ends NNNN. ZCZC is the start marker. F is the B1 station identifier, A is the B2 message type for a navigational warning, and 01 is the serial number. The operator should check that station F and type A are selected, and that the warning applies to the vessel's area. The reasoning: the header tells the receiver and the watchkeeper what station sent the message, what kind of message it is, and whether it is new or a repeat.
Traps
518 kHz is not the only NAVTEX frequency; 490 kHz is national and may be in a local language. Do not assume NAVTEX is received if the receiver is on but the station and type selections exclude the message. Do not confuse SafetyNET EGC with ordinary Inmarsat-C mail. Do not ignore the NNNN end marker when decoding. Do not treat a NAVTEX test message as an operational warning. Do not disable EGC in an A3 vessel that relies on SafetyNET.
Key facts
NAVTEX international is 518 kHz English. Header is ZCZC B1B2B3B4. SafetyNET uses Inmarsat EGC. MSI includes navigation and meteorological warnings.