Statutory Documents - IMO Publications and Documents - Circulars - Maritime Safety Committee - MSC.1/Circular.1403 – Revised NAVTEX Manual – (23 May 2011) - Annex - 7 Message Format
7 Message Format
7.1 NAVTEX messages must be composed in accordance to the guidelines contained in the Joint IMO/IHO/WMO Manual on Maritime Safety Information and IHO Publication S-53. The format of all messages shall be in strict accordance with Figure 6 . This defines the essential elements of the messages which influence the operation of the receiver. Great care is required to avoid errors of syntax in the groups ZCZC B1B2B3B4 and NNNN as they will cause receivers to operate incorrectly, and may well result in messages not being received.
Figure 6 Standard format for NAVTEX messages
7.2 The phasing signal is automatically transmitted by the NAVTEX transmitter at the beginning of each message and is critical to the effective operation of the system. It is this signal which enables a receiver to lock-on to a particular station's transmission, providing the frequency is not already in use.
7.3 If another station within transmitting range and with a time slot prior to the station selected overruns its time slot (regardless of the B1 transmitter identification character in use), its transmission will blank the phasing signal of the subsequent transmitter. It will then seem to the receiver as if the second station is off the air and its broadcast will not be received, possibly denying the user significant safety information. This is the primary reason behind the importance of each station adhering to its allocated time slots. Similarly if the phasing signal for a particular station is too short, some receivers will be unable to lock on to the transmission.
7.4 Basic message elements:
Table 3 Basic message elements
| Element | Example |
| Phasing signal | |
| Start of message group | ZCZC |
| One space | |
| NAVTEX message identity | FA01 |
| Carriage return + line feed | |
| Message content | (Date Time Group – Optional e.g.
040735 UTC OCT 10) NAV I 114/10 ENGLISH CHANNEL. START POINT SOUTHWARD. CHART BA 442 (INT 1701). UNEXPLODED ORDNANCE LOCATED 49-51.97N 003-39.54W AND 49-55.24N 003-40.79W. |
| End of message instruction | NNNN |
| Carriage return + two line feeds | |
| Phasing signal |
7.5 When a message has been received error-free, a record is made by the receiver of the NAVTEX message identity. This unique identifier is used to suppress the printing or display of repeated transmissions of the same message.
7.6 On national NAVTEX services it is important to keep to the same basic message format as that required for the International NAVTEX service. It is also important to ensure that the full broadcast does not overrun the allocated time slot. However, in order to meet national requirements, message content may deviate from the guidelines provided for the International NAVTEX Service if required.
| Copyright 2016 Clasification Society, International Maritime Organization, International Labour Organization or Maritime and Coastguard Agency. All rights reserved. Clasification Society, its affiliates and subsidiaries and their respective officers, employees or agents are, individually and collectively, referred to in this clause as 'Clasification Society'. Clasification Society Register assumes no responsibility and shall not be liable to any person for any loss, damage or expense caused by reliance on the information or advice in this document or howsoever provided, unless that person has signed a contract with the relevant Clasification Society entity for the provision of this information or advice and in that case any responsibility or liability is exclusively on the terms and conditions set out in that contract. |  |