Satellite Communications, NAVTEX, SafetyNET and SafetyCAST
Satellite MSI
Inmarsat is the classic A3 provider. SafetyNET is its Enhanced Group Call service for maritime safety information, addressed to a sea area or a group. Iridium provides a comparable GMDSS service with SafetyCAST. Both deliver navigational warnings, meteorological warnings and SAR information to ships outside coastal NAVTEX coverage.
NAVTEX
The international NAVTEX frequency is 518 kHz, with transmissions in English. National-language NAVTEX commonly uses 490 kHz, and 4209.5 kHz is used in some regions. A NAVTEX receiver must be set to the correct station, message types and transmitter schedule. Message types include navigational warnings, meteorological warnings, ice reports, SAR information, forecasts, pilot messages and electronic navigation system messages.
Reception practice
Do not treat one system as a backup for the other without checking coverage. NAVTEX is coastal, typically a few hundred nautical miles; SafetyNET/SafetyCAST is wide-area. The receiver must be powered and configured, and the operator must read and act on the message, not merely leave the printer running.
Worked example: a yacht on an A3 passage receives a gale warning by SafetyNET, while approaching Italy it receives coastal navigational warnings on NAVTEX 518 kHz. The reasoning: the offshore area is outside reliable NAVTEX coverage, so the satellite EGC service is the primary MSI path; near the coast NAVTEX becomes the local source.
Traps
518 kHz is the international English NAVTEX frequency; 490 kHz is normally national language. SafetyNET is not NAVTEX and does not use 518 kHz. A receiver that is switched off or set to the wrong message types provides no service. Do not rely on a single MSI source when the vessel is in an area covered by both.