Navtex OnlineWhat is NAVTEX?
NAVTEX is an international radio service that sends maritime safety information as text to ships: navigational warnings, weather warnings and forecasts, ice reports and search-and-rescue alerts. A small receiver on board prints or stores the messages automatically. It is part of the Global Maritime Distress and Safety System (GMDSS): ships covered by the SOLAS convention must carry a NAVTEX receiver when they sail where NAVTEX is provided.
Frequencies and range
518 kHzis the international service, always in English.490 kHzand4209.5 kHzcarry national services, in the language each country chooses: often the national language, sometimes English.- A station is designed to reach about 250–400 nautical miles. At night signals travel further, so distant stations on the same letter can sometimes be heard.
Time slots
Stations in one region share a frequency. Each has a letter A–X and may only transmit in its own 10-minute slot, which repeats every 4 hours. Stations far enough apart reuse the same letters.
When messages go out
- Urgent messages, such as distress relays, piracy and tsunami warnings, go out at once, outside the slot if needed. Important ones, such as gale warnings, go out at the next free moment.
- Warnings are repeated in every slot while they are in force. Coastal warnings may stop after six weeks if they are published elsewhere, for example in Notices to Mariners.
- Weather forecasts go out at least twice a day, relevant NAVAREA warnings at least twice a day, and a list of warnings in force about once a week.
- A cancellation is sent once; the cancelled warning is no longer repeated.
Message format
Messages are sent at 100 baud using SITOR-B (forward error correction): every character goes out twice. If both copies are damaged, the receiver prints an asterisk *; some decoders use _ instead.
Every message starts with ZCZC B1B2B3B4 and ends with NNNN. B1 is the station letter, B2 the subject (what kind of message), B3B4 a serial number 01–99. This serial only identifies the broadcast; it is not the warning's own number (such as WZ 692/26), which is in the text.
A receiver remembers each B1B2B3B4 it received cleanly (fewer than 4% bad characters) for 60–72 hours and skips repeats of it, so a garbled copy is printed again when the message is repeated. Serial 00 is reserved for urgent messages and is always printed.
A receiver can switch off subjects it does not want, except A (navigational warnings), B (meteorological warnings), D (search and rescue) and L (more navigational warnings, used when over 99 A messages are in force). Subject D also sounds an alarm. All subject letters and how to read a message →
The regions
Warnings are organised in 21 NAVAREAs, each with a coordinator; weather uses METAREAs with the same numbers and largely the same limits. NAVTEX stations (orange) serve the coasts inside them. What is a NAVAREA →
Where the messages on this site come from
NAVTEX is a radio service, and there is no single official internet feed of what is broadcast. This site combines copies from receivers that publish what they hear, operators that publish their own transmit log, and official lists of warnings in force from national and NAVAREA coordinators. Where several copies of a message exist, the cleanest is shown, with the official text where it matches. See data sources.
Reference: IMO NAVTEX Manual (MSC.1/Circ.1403/Rev.2). Diagrams redrawn for this site.