How to read a Navtex message
20 March 2018
We recently wrote a blog about Navtex and its uses. However, once installed, there are a few things one needs to understand before a Navtex receiver can be used effectively. In particular, it’s important to understand the shorthand used when navtex information is transmitted.
As an example, here is a navtex message for consideration;
241046 UTC MAY 07
ANTALYA TURK RADIO
NAVTEX NW NR:298/07
EASTERN MEDITERRANEAN YACHT RALLY,
FROM 24 MAY 07 TO 19 JUN 07,
RALLY ROUTES MERSIN, ISKENDERUN,
LATTAKIA, JOUNEH, HAIFA, ASHKELON,
PORT SAID AND HERZLIYA, ALL VESSELS IN
THE REGION REQUESTED TO FOLLOW
THE NOTICE DECLARED BY AUTHORITES
WIDE BERTH ADVISED
Going section-by-section, the message can be explained as follows;
Line 1 - ZCZC indicates the start of a message. F indicates the geographic area and A60 indicates the ‘subject’ of the message. For example, ‘A’ classifies the message as a ‘Navigational Warning’.
Line 2 - 241046 UTC MAY 07. Clearly, this is the date and time in UTC.
Line 3 - ANTALYA TURK RADIO. This is the transmitting CRS (Coast Radio station).
Line 4 - onwards - NAVTEX NW NR:298/07. This is the Navtex message reference followed by the message itself.
Last Line - NNNN indicates the end of message.
The subject indicator in a Navtex message is defined as follows;
A Navigational warnings (cannot be rejected by the receiver)
B Meteorological warnings (cannot be rejected by the receiver)
C Ice reports
D SAR (Search And Rescue) information and pirate attack warnings (cannot be rejected by the receiver)
E Meteorological forecasts
F Pilot service messages
G AIS (Automatic Identification System)
H LORAN (LOng RAnge Navigation system) messages
I Available if required
J SATNAV (Satellite Navigation Systems, for example United States Global Positioning System (GPS); USSR GLONASS system; Future (2008) EU GALILEO system) messages
K Other electronic Navaid messages (messages concerning radio navigation services)
L Navigational warnings – additional to letter Subject indicator A (should not be rejected by the receiver)
V Special Services – allocation by the NAVTEX panel
W Special Services – allocation by the NAVTEX panel
X Special Services – allocation by the NAVTEX panel
Y Special Services – allocation by the NAVTEX panel
Z No messages on hand
In addition, various countries also have specific uses for subjects listed above. In the UK, L is used for Sub facts, Gun facts and Oil Rig movements warnings (should not be rejected by the receiver) and V for Amplifying Navigational warnings initially announced in letter A.
Finally, if there is an error percentage before the start of the message this illustrates the percentage of letters that are incorrect in the message. For example, a 3% error in a 100 word message would be 3 incorrect characters.