Foreword

SOLAS regulation IV/12.2 states that "Every ship, while at sea, shall maintain a radio watch for broadcasts of maritime safety information on the appropriate frequency or frequencies on which such information is broadcast for the area in which the ship is navigating".

At the request of the IMO Sub-Committee on Radiocommunications (COM), the NAVTEX Manual was first produced in 1988. Three subsequent editions have been produced, with the fourth edition published in 2005 containing amendments endorsed by the Maritime Safety Committee (MSC) at its seventy-eighth session in May 2004 by MSC/Circ.1122.

At its seventh meeting in September 2005, the IHO Commission on the Promulgation of Radio Navigational Warnings (CPRNW)^footnote established a working group to review all World-Wide Navigational Warning Service (WWNWS) documentation. The working group included representation from the WMO and firstly prepared revisions to resolutions A.705(17), Promulgation of Maritime Safety Information and A.706(17), World-Wide Navigational Warning Service. The proposed revisions of these resolutions were circulated to IHO Member States under IHB CL 104/2007, endorsed by the Sub-Committee on Radiocommunications and Search and Rescue (COMSAR) at its twelfth session in April 2008 and subsequently approved by the MSC at its eighty-fifth session in November/December 2008 by means of MSC.1/Circ.1287 and MSC.1/Circ.1288, respectively.

The IHO CPRNW Working Group then prepared the revised Joint IMO/IHO/WMO Manual on Maritime Safety Information incorporating the revised information from resolutions A.705(17), as amended, and A.706(17), as amended. The revised text was circulated to IHO Member States under cover of IHB CL 70/2008, endorsed by the COMSAR Sub-Committee at its thirteenth session in January 2009 and subsequently approved by the MSC at its eighty-sixth session in May/June 2009 by means of MSC.1/Circ.1310. The working group subsequently prepared the third revision of the International SafetyNET Manual. The revised text of the International SafetyNET Manual was circulated to IHO Member States under cover of IHB CL 68/2009, endorsed by the COMSAR Sub-Committee at its fourteenth session in March 2010 and approved by the MSC at its eighty-seventh session in May 2010 by MSC.1/Circ.1364.

Continuing with the holistic approach of reviewing all maritime safety information documents from the top-down, the working group prepared the fifth revision of the NAVTEX Manual. The revised text of the NAVTEX Manual was circulated to IHO Member States under cover of IHB CL 74/2010, endorsed by the COMSAR Sub-Committee at its fifteenth session in March 2011 and subsequently approved by the MSC at its eighty-ninth session in May 2011 by MSC.1/Circ.1403.

Following the review of all WWNWS documentation, an editorial review has been conducted. As part of this editorial review, MSC.1/Circ.1287/Rev.1 and MSC.1/Circ.1288/Rev.1 were approved by the MSC at its ninety-second session in June 2013, and MSC.1/Circ.1310/Rev.1 was approved by the MSC at its ninety-fourth session in November 2014. Following the approval of these circulars, the IHO WWNWS Sub-Committee Working Group reviewed the text of the NAVTEX Manual. This sixth revision of the NAVTEX Manual was endorsed by the IHO and the WMO through the WWNWS Sub-Committee, endorsed by the Sub-Committee on Navigation, Communications and Search and Rescue (NCSR) at its third session in February/March 2016 and subsequently approved by the MSC at its ninety-seventh session in November 2016 by means of MSC.1/Circ.1403/Rev.1, with an entry into force date of 1 January 2018.

1 General information

1.1 NAVTEX is an international automated direct-printing service for promulgation of Maritime Safety Information (MSI), navigational and meteorological warnings, meteorological forecasts and other urgent safety-related messages to ships. It was developed to provide a low-cost, simple and automated means of receiving MSI on board ships at sea in coastal waters. The information transmitted may be relevant to all sizes and types of vessel and the selective message-rejection feature ensures that mariners can receive MSI broadcasts which are tailored to their particular needs.

1.2 NAVTEX fulfils an integral role in the Global Maritime Distress and Safety System (GMDSS) developed by the International Maritime Organization (IMO) and incorporated into the 1988 amendments to the International Convention for the Safety of Life at Sea (SOLAS), 1974, as amended, as a requirement for ships to which the Convention applies.

1.3 This Manual describes the structure and operation of the NAVTEX service. It is intended primarily for use by national Administrations and others concerned with the preparation and broadcasting of MSI. It will also be of interest to seafarers, shipowners and others who need to receive such information in order to safely go about their business at sea. It should be used in conjunction with the Joint IMO/IHO/WMO Manual on Maritime Safety Information (also published as the IHO/IMO World-Wide Navigational Warning Service Guidance Document, IHO Publication S-53).

2 NAVTEX service

2.1 Introduction

2.1.1 NAVTEX provides shipping with navigational and meteorological warnings, meteorological forecasts and other urgent safety-related messages (as listed in table 1, section 5) by automatic display or printout from a dedicated receiver. It is suitable for use in all sizes and types of ships. Figure 1 illustrates the way the service is typically structured.

Figure 1 – Basic concept of the NAVTEX system

2.1.2 NAVTEX is a component of the IMO/IHO World-Wide Navigational Warning Service (WWNWS) defined by resolutions A.706(17), as amended, and A.1051(27), as amended. It has also been included as an element of the Global Maritime Distress and Safety System (GMDSS).

2.1.3 In the GMDSS, a NAVTEX receiving capability is part of the mandatory equipment which is required to be carried in certain vessels under the provisions of the International Convention for the Safety of Life at Sea (SOLAS), 1974, as amended.

2.1.4 Authority for coordinating the use of the frequencies 518 kHz, 490 kHz and 4209.5 kHz for NAVTEX services worldwide was delegated by ITU to IMO at WRC-95 through resolution 339. This was reaffirmed at WRC-97. IMO has vested responsibility for the overall management and coordination of the global NAVTEX service to the NAVTEX Coordinating Panel. With respect to National NAVTEX broadcasts on 490 kHz and 4209.5 kHz, the function of the NAVTEX Coordinating Panel is limited to the allocation of transmission identification characters.^footnote It should be noted that the provisions of the NAVTEX Manual do not apply when planning a National NAVTEX service on other nationally assigned frequencies. The Terms of Reference for this Panel are attached in annex 1.

2.1.5 Details of operational and planned NAVTEX services are published periodically in the various national lists of radio signals, in an annex to the International Telecommunication Union's (ITU) List IV – List of coast stations and special service stations, and in the GMDSS Master Plan published by IMO in its series of GMDSS Circulars.

2.2 Definitions

2.2.1 For the purposes of this Manual, the following definitions apply:

.1 Coastal warning means a navigational warning or in-force bulletin promulgated as part of a numbered series by a National Coordinator. Broadcast should be made by the International NAVTEX service to defined NAVTEX service areas and/or by the International SafetyNET service to coastal warning areas. (In addition, Administrations may issue coastal warnings by other means).
.2 Coastal warning area means a unique and precisely defined sea area within a NAVAREA/METAREA or Sub-area established by a coastal State for the purpose of coordinating the broadcast of coastal maritime safety information through the SafetyNET service.
.3 Global Maritime Distress and Safety System (GMDSS) means the global communications service based upon automated systems, both satellite and terrestrial, to provide distress alerting and promulgation of maritime safety information for mariners.
.4 HF NBDP means High Frequency narrow-band direct-printing, using radio telegraphy as defined in Recommendation ITU-R M.688.
.5 In-force bulletin means a list of serial numbers of those NAVAREA, Sub-area or coastal warnings in force issued and broadcast by the NAVAREA Coordinator, Sub-area Coordinator or National Coordinator.
.6 International NAVTEX service means the coordinated broadcast and automatic reception on 518 kHz of maritime safety information by means of narrow-band direct-printing telegraphy using the English language.^footnote
.7 International SafetyNET service means the coordinated broadcast and automatic reception of maritime safety information via the Inmarsat Enhanced Group Call (EGC) system, using the English language, in accordance with the provisions of the International Convention for the Safety of Life at Sea, 1974, as amended.
.8 Issuing Service means a National Meteorological Service which has accepted responsibility for ensuring that meteorological warnings and forecasts for shipping are disseminated through the International SafetyNET service to the METAREA for which the Service has accepted responsibility under the broadcast requirements of the GMDSS..^footnote
.9 Local warning means a navigational warning which covers inshore waters, often within the limits of jurisdiction of a harbour or port authority.
.10 Maritime safety information (MSI)^footnote means navigational and meteorological warnings, meteorological forecasts and other urgent safety-related messages broadcast to ships.
.11 Maritime safety information service means the internationally and nationally coordinated network of broadcasts containing information which is necessary for safe navigation.
.12 METAREA means a geographical sea area* established for the purpose of coordinating the broadcast of marine meteorological information. The term METAREA followed by a roman numeral may be used to identify a particular sea area. The delimitation of such areas is not related to and shall not prejudice the delimitation of any boundaries between States. (See figure 2).

*Which may include inland seas, lakes and waterways navigable by seagoing ships.
.13 METAREA Coordinator means the authority charged with coordinating marine meteorological information broadcasts by one or more National Meteorological Services acting as Preparation or Issuing Services within the METAREA.
.14 Meteorological information means the marine meteorological warning and forecast information in accordance with the provisions of the International Convention for the Safety of Life at Sea, 1974, as amended.
.15 National Coordinator means the national authority charged with collating and issuing coastal warnings within a national area of responsibility.
.16 National NAVTEX service means the broadcast and automatic reception of maritime safety information by means of narrow-band direct-printing telegraphy using frequencies other than 518 kHz and languages as decided by the Administration concerned.
.17 National SafetyNET service means the broadcast and automatic reception of maritime safety information via the Inmarsat EGC system, using languages as decided by the Administration concerned.
.18 NAVAREA means a geographical sea area* established for the purpose of coordinating the broadcast of navigational warnings. The term NAVAREA followed by a roman numeral may be used to identify a particular sea area. The delimitation of such areas is not related to and shall not prejudice the delimitation of any boundaries between States. (See figure 3).

*Which may include inland seas, lakes and waterways navigable by seagoing ships.
.19 NAVAREA Coordinator means the authority charged with coordinating, collating and issuing NAVAREA warnings for a designated NAVAREA.
.20 NAVAREA warning means a navigational warning or in-force bulletin promulgated as part of a numbered series by a NAVAREA Coordinator.
.21 Navigational warning means a message containing urgent information relevant to safe navigation broadcast to ships in accordance with the provisions of the International Convention for the Safety of Life at Sea, 1974, as amended.
.22 NAVTEX means the system for the broadcast and automatic reception of maritime safety information by means of narrow-band direct-printing telegraphy.^footnote
.23 NAVTEX Coordinator means the authority charged with operating and managing one or more NAVTEX stations broadcasting maritime safety information as part of the International NAVTEX service.
.24 NAVTEX coverage area means an area defined by an arc of a circle having a radius from the transmitter calculated according to the method and criteria given in resolution A.801(19), as amended, see annex 4.
.25 NAVTEX service area means a unique and precisely defined sea area, wholly contained within the NAVTEX coverage area, for which maritime safety information is provided from a particular NAVTEX transmitter. It is normally defined by a line that takes full account of local propagation conditions and the character and volume of information and maritime traffic patterns in the region, as given in resolution A.801(19), as amended, see annex 4.
.26 Other urgent safety-related information means maritime safety information broadcast to ships that is not defined as a navigational warning or meteorological information. This may include, but is not limited to, significant malfunctions or changes to maritime communications systems, and new or amended mandatory ship reporting systems or maritime regulations affecting ships at sea.
.27 Rescue Coordination Centre (RCC) () means a unit responsible for promoting efficient organization of search and rescue services and for coordinating the conduct of search and rescue operations within a search and rescue region. Note: The term RCC will be used within this Manual to apply to either joint, aeronautical or maritime centres; JRCC, ARCC or MRCC will be used as the context warrants.
.28 SafetyNET means the international service for the broadcast and automatic reception of maritime safety information via the Inmarsat EGC system. SafetyNET receiving capability is part of the mandatory equipment which is required to be carried by certain ships in accordance with the provisions of the International Convention for the Safety of Life at Sea, 1974, as amended.
.29 SAR information means distress alert relays and other urgent search and rescue information broadcast to ships.
.30 Sub-area means a subdivision of a NAVAREA/METAREA in which a number of countries have established a coordinated system for the promulgation of maritime safety information. The delimitation of such areas is not related to and shall not prejudice the delimitation of any boundaries between States.
.31 Sub-area Coordinator means the authority charged with coordinating, collating and issuing Sub-area warnings for a designated Sub-area.
.32 Sub-area warning means a navigational warning or in-force bulletin promulgated as part of a numbered series by a Sub-area Coordinator. Broadcast should be made by the International NAVTEX service to defined NAVTEX service areas or by the International SafetyNET service (through the appropriate NAVAREA Coordinator).
.33 UTC means Coordinated Universal Time which is equivalent to GMT (or ZULU) as the international time standard.
.34 World-Wide Met-ocean Information and Warning Service (WWMIWS)^footnote means the internationally coordinated service for the promulgation of meteorological warnings and forecasts.
.35 World-Wide Navigational Warning Service (WWNWS)^footnote means the internationally and nationally coordinated service for the promulgation of navigational warnings.
.36 In the operating procedures, coordination means that the allocation of the time for data broadcast is centralized, the format and criteria of data transmissions are compliant as described in the Joint IMO/IHO/WMO Manual on Maritime Safety Information and that all services are managed as set out in resolutions A.705(17), as amended, A.706(17), as amended, and A.1051(27), as amended.

2.2.2 Delimitation of METAREAs

Figure 2 – METAREAs for coordinating and promulgating navigational warnings under the World-Wide Navigational Warning Service

The delimitation of such areas is not related to and shall not prejudice the delimitation of any boundaries between States.

2.2.3 Delimitation of NAVAREAs

Figure 3 – NAVAREAs for coordinating and promulgating meteorological warnings and forecasts within the GMDSS

The delimitation of such areas is not related to and shall not prejudice the delimitation of any boundaries between States.

3 General features of the NAVTEX system

3.1 The principal features are:

.1 use of a single frequency, with transmissions from stations within and between NAVAREAs and METAREAs coordinated on a time-sharing basis to reduce the risk of mutual interference. The following frequencies may be used for NAVTEX broadcasts:

518 kHz
Type of service:	International
Content:	Maritime safety information
Language:	English
Coordination:	By IMO NAVTEX Coordinating Panel
490 kHz and 4209.5 kHz
Type of service:	National
Content:	Maritime safety information
Language:	As selected by the national Administration
Coordination:	Transmitter identification character allocated by IMO NAVTEX Coordinating Panel
Other national frequencies allocated by the ITU
Type of service:	National
Content:	As selected by the national Administration
Language:	As selected by the national Administration
Coordination:	By appropriate national Administration

.2 a dedicated NAVTEX receiver, comprising radio receivers, a signal processor and either:
- .2.1 an integrated printing device; or
- .2.2 a dedicated display device with a printer output port and a non-volatile message memory; or
- .2.3 a connection to an integrated navigation system and a non-volatile message memory;
  which has the ability to select messages to be printed, or viewed and stored in a memory according to:
  - a technical code (B₁B₂B₃B₄), which appears in the preamble of each message; and
  - whether or not the particular message has already been printed/received.

3.2 The operational and technical characteristics of the NAVTEX system are contained in Recommendation ITU-R M.540-2^footnote. Performance standards for shipborne equipment, if installed before 1 July 2005, are laid down in resolution A.525(13). If installed on or after 1 July 2005, they shall conform to resolution MSC.148(77).^footnote

4 Planning NAVTEX services

4.1 When planning NAVTEX services, Administrations should obtain guidance at an early stage from IMO, through its NAVTEX Coordinating Panel. This may be particularly important when installation of new stations and/or purchase of new equipment is under consideration. Details of how to contact the Panel may be found in annex 1.

4.2 International NAVTEX services on 518 kHz

When planning an International NAVTEX service it is essential to appreciate the high level of national and international coordination required. The central principles which should be borne in mind are as follows:

.1 All NAVTEX stations are part of the strategic infrastructure of both the GMDSS and WWNWS.
.2 It is essential for the efficiency and effectiveness of the service that a minimum number of stations are used. This may require national Administrations to either share facilities or promulgate information provided by Administrations of other nations.
.3 Each station contributes to the overall service in a coordinated way, bearing in mind the geographical area covered by each station and the effective coordination and control of information to be transmitted.
.4 The two basic areas which must be defined when establishing a NAVTEX station are the NAVTEX coverage area and the NAVTEX service area. Each station will provide all the information for a particular NAVTEX service area. The boundaries of the NAVTEX service area must be wholly contained within the coverage area, and must not overlap with adjacent NAVTEX service areas (see figure 4).
.5 National Administrations seeking to establish NAVTEX services shall undertake preliminary discussions with the NAVAREA Coordinator, METAREA Coordinator and neighbouring Administrations prior to formal application to IMO through the IMO NAVTEX Coordinating Panel. These discussions shall consider the most appropriate NAVTEX service area boundaries, possible geographical locations for transmitter sites to ensure optimal coverage and links with Information Providers.
.6 The range of a NAVTEX transmitter depends on the transmitted power and local radio propagation conditions. The actual range achieved shall be adjusted to the minimum required for adequate reception in the specified NAVTEX service area, taking into account the needs of ships approaching from other areas. Experience indicates that the required range of 250 to 400 nautical miles will normally be attained by transmitted power of no more than 1 kW during daylight with a 60% reduction during night conditions.
.7 After the choice of transmitter sites, the main need for coordination lies in the assignment of B₁ transmitter identification characters (time schedules) and the agreement of proposed NAVTEX service areas (if appropriate). Preliminary discussions between national Administrations seeking to establish or amend NAVTEX services and neighbouring Administrations shall be coordinated by the NAVAREA Coordinator prior to formal application for a B₁ transmitter identification character. Throughout the process the IMO NAVTEX Coordinating Panel is available to advise and liaise on the final limits of NAVTEX service areas if these cannot be agreed locally.
.8 The IMO NAVTEX Coordinating Panel will only allocate B₁ transmitter identification characters after the NAVTEX service areas have been agreed.
.9 Once a NAVTEX transmitter has been declared operational, if a national Administration wishes to:
- .9.1 move the transmitter site; and/or
- .9.2 amend the limits of its NAVTEX service area,
- then the whole coordination process outlined above must be repeated, keeping the NAVTEX Coordinating Panel informed at all times.
.10 A National NAVTEX Coordinator shall be established to oversee the operation of the NAVTEX services established by each national Administration. The responsibilities of the NAVTEX Coordinator are defined in section 12 of this Manual.

Figure 4 – Example of NAVTEX service areas

The Baltic Sea and its approaches have been divided into five individual NAVTEX service areas. Within each service area, maritime safety information is provided from a separate NAVTEX station which has been allocated a dedicated B₁ transmitter identification character. It is a fundamental requirement that the range of each NAVTEX transmitter is sufficient to include the whole of the NAVTEX service area assigned to its B₁ transmitter identification character.

4.3 National NAVTEX services on 490 kHz or 4209.5 kHz

The provisions of the NAVTEX Manual apply to National NAVTEX services on 490 kHz or 4209.5 kHz. When planning a National NAVTEX service, the IMO NAVTEX Coordinating Panel is responsible for the allocation of B₁ transmitter identification characters; however, the establishment of NAVTEX service areas and the compulsory use of the English language are not required.

4.4 National NAVTEX services on other frequencies

The provisions of the NAVTEX Manual do not apply when planning a National NAVTEX service on nationally assigned frequencies.

5 NAVTEX message technical characters

5.1 Overview of technical characters, B₁, B₂, B₃, B₄

5.1.1 NAVTEX messages include instructions to the NAVTEX receiver for processing maritime safety information in the form of the NAVTEX message identity, which consists of four technical "B" characters which make up an alphanumeric code. In order for messages to be correctly processed, they must consist of data conforming to these "B" characters:

B₁ Transmitter identification character
B₂ Subject indicator character
B₃B₄ Message numbering characters

5.2 B₁ – Transmitter identification character

5.2.1 The transmitter identification character (B₁) is a single letter which is allocated to each transmitter. It is used to identify the broadcasts which are to be accepted by the receiver and those to be rejected, and also the time slot for the transmission.

5.2.2 In order to avoid erroneous reception and interference of transmissions from two stations having the same transmitter identification character, it is necessary to ensure that such stations have a large geographical separation. Allocation of transmitter identification characters by alphabetical sequence to adjacent sites can also cause problems; hence, consecutive transmitter identification characters are not normally allocated to adjacent stations. Experience has shown that this removes the risk of a station which over-runs its time slot masking the phasing signal of an adjacent station which is about to begin its transmission.

Table 1 – Technical "B" characters which make up the full NAVTEX message identity^footnote, ^footnote

B₁ Transmitter identification character	B₂ Subject indicator character		B₃ B₄ Message numbering characters
1 letter	1 letter		2 digits
A to X	A = Navigational warnings		01 to 99 (message numbering characters "00" are not to be used for routine messages)
	B = Meteorological warnings
	C = Ice reports
	D = Search and rescue information, acts of piracy warnings, tsunamis and other natural phenomena
	E = Meteorological forecasts
	F = Pilot and VTS service messages
	G = AIS service messages (non-navigational aid)
	H = LORAN messages
	I = Currently not used
	J = GNSS messages regarding PRN status
	K = Other electronic navigational aid system messages
	L = Other navigational warnings – additional to B₂ character A¹⁶
	M =
	N = O = P = Q = R =	Currently not used
	S =
	T =
	U =
	V =
	W= X = Y =	Special services allocation by the IMO NAVTEX Coordinating Panel
	Z = No message on hand

Figure 5 – Example of NAVTEX receiver with LCD screen

5.2.3 NAVTEX transmissions have a designed maximum range of about 400 nautical miles. The minimum distance between two transmitters with the same transmitter identification identifier must, therefore, be sufficient to ensure that a receiver cannot be within range of both at the same time.

5.2.4 Close coordination between transmitting stations in adjacent NAVAREAs/METAREAs is necessary to achieve this separation. For this reason, national Administrations shall request the advice of the IMO NAVTEX Coordinating Panel at an early stage in the planning of a new NAVTEX service. The Panel will allocate B₁ transmitter identification characters in such a way as to minimize the risk of interference occurring.

5.2.5 Table 2 shows the transmitter identification characters and their associated transmission start times used by the IMO NAVTEX Coordinating Panel to evaluate and allocate transmitter identification characters A to X, regardless of the geographical position of the station anywhere in the world. Each transmitter identification character is allocated a maximum transmission time of 10 minutes every 4 hours. Because the NAVTEX system always utilizes a single frequency, it is fundamental to its successful operation that the following time slots are strictly adhered to, and that broadcasts do not overrun their allotted 10 minutes.

Table 2 – NAVTEX transmission start times

Transmitter identification character (B₁)	Transmission start times (UTC
A	0000	0400	0800	1200	1600	2000
B	0010	0410	0810	1210	1610	2010
C	0020	0420	0820	1220	1620	2020
D	0030	0430	0830	1230	1630	2030
E	0040	0440	0840	1240	1640	2040
F	0050	0450	0850	1250	1650	2050
G	0100	0500	0900	1300	1700	2100
H	0110	0510	0910	1310	1710	2110
I	0120	0520	0920	1320	1720	210
J	0130	0530	0930	1330	1730	2130
K	0140	0540	0940	1340	1740	2140
L	0150	0550	0950	1350	1750	2150
M	0200	0600	1000	1400	1800	2200
N	0210	0610	1010	1410	1810	2210
O	0220	0620	1020	1420	1820	2220
P	0230	0630	1030	1430	1830	2230
Q	0240	0640	1040	1440	1840	2240
R	0250	0650	1050	1450	1850	2250
S	0300	700	1100	1500	1900	2300
T	0310	0710	1110	1510	1910	2310
U	0320	0720	1120	1520	1920	2320
V	0330	0730	1130	1530	1930	2330
W	0340	0740	1140	1540	1940	2240
X	0350	0750	1150	1550	1950	2250

5.2.6 In some regions, it has become necessary to accommodate a large number of stations. In extreme cases, it has even been necessary to reuse some transmitter identification characters for a second time within a region. Where this occurs every effort is made to ensure stations with the same character are as far apart as possible to reduce the risk of mutual interference.

5.3 B₂ – Subject indicator character

5.3.1 Information is grouped by subject in the NAVTEX broadcast and each subject group is allocated a B₂ subject indicator character.

5.3.2 The subject indicator character is used by the receiver to identify the different classes of messages as listed in table 1.

5.3.3 Some subject indicator characters can be used to reject messages concerning certain subjects which may not be required by the ship (e.g. Ice report messages may be rejected by deselecting the B₂ subject indicator character C on the NAVTEX receiver on board a ship.).

5.3.4 Reception of messages, transmitted using subject indicator characters A, B, D and L, which have been allocated for navigational warnings, meteorological warnings, search and rescue information, acts of piracy warnings, tsunamis and other natural phenomena, is mandatory and cannot be deselected on the NAVTEX receiver. This has been designed to ensure that ships using NAVTEX always receive the most essential information.

5.3.5 It is not possible to transmit or receive two NAVTEX messages with the same NAVTEX message identity (made up of the four technical characters). Therefore the B₂ subject indicator character L has been designated for use in the unlikely event that a NAVTEX Coordinator has more than 99 navigational warning messages in force and requiring transmission at the same time, all using B₂ subject indicator character A, with the same B₁ transmitter identification character.

5.3.6 Messages received which have been transmitted using subject indicator character D will set off an alarm built into the NAVTEX receiver.

5.3.7 In the International NAVTEX service, Administrations shall obtain the agreement of the IMO NAVTEX Coordinating Panel for all proposals for the use of special service subject indicator characters. Such proposals shall meet the following criteria:

.1 The full international service must remain unaffected.
.2 The special service broadcasts shall be transmitted only when time allows, and with due regard to the necessity for the frequency to remain unused for a high percentage of the time.
.3 The special service broadcast shall only be used for its approved purpose.

5.4 B₃B₄ – Message numbering characters (NAVTEX number)

5.4.1 Each message within each subject group is allocated a two digit sequential serial number beginning at 01 and ending at 99. The B₃B₄ message numbering characters together, are often referred to as the "NAVTEX number".

5.4.2 The NAVTEX number is solely allocated as a component of the NAVTEX message identity and should not be confused with (and bears no correlation to), the series identity and consecutive number of the NAVAREA or Coastal warning contained in the message.

5.4.3 Messages broadcast using NAVTEX number B₃B₄ = 00 cannot be rejected and will automatically override any selection of B₁ transmitter identification characters as well as any B₂ subject indicator characters selected on the NAVTEX receiver.

5.4.4 Use of NAVTEX number B₃B₄ = 00 must therefore be strictly controlled, since messages carrying it will always be printed or displayed every time they are received. Routine messages and service messages must never be allocated B₃B₄ = 00. The correct use of B₂ characters A, B, D and L, will ensure that messages containing safety information will always be printed or displayed on first receipt.

6 Message identity

6.1 The individual NAVTEX message identity is the amalgamation of all four technical characters B₁B₂B₃B₄ (transmitter identification character/subject indicator character/message numbering characters).

6.2 When a message is received for the first time by a NAVTEX receiver, the message identity is recorded and stored in the memory for 72 hours. This ensures that subsequent transmissions of the same message are not re-printed or repeated in the display, unless they are re-received over 72 hours later. In the unlikely event that all 99 NAVTEX numbers for a particular subject group, from a particular transmitter, are in use at the same time, or have been allocated within the past 72 hours, an alternative B₂ character must be utilized; for example, B₂ = L has been set aside to be used for additional navigational warnings if all 99 NAVTEX numbers for subject group B₂ = A are in use.

6.3 Each NAVTEX message identity shall be allocated by the relevant NAVTEX Coordinator, who is the authority responsible for the selection of information to be broadcast by each transmitter within each subject group. A single NAVTEX Coordinator may have more than one transmitter under their control. Specific advice on the use of alternative B₂ subject indicator characters as mentioned in 6.2 above, can be provided by the IMO NAVTEX Coordinating Panel.

7 Message format

7.1 NAVTEX messages must be composed in accordance with the guidelines contained in the Joint IMO/IHO/WMO Manual on Maritime Safety Information and IHO Publication S-53. The format of all messages must 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 17) NAV I 114/17 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.

7.7 Examples of navigational warning messages

Note: Further examples are available for consultation in the Joint IMO/IHO/WMO Manual on Maritime Safety Information.

7.8 Examples of meteorological messages

Note: Further examples are available for consultation in the Joint IMO/IHO/WMO Manual on Maritime Safety Information.

8 Language and national broadcast options

8.1 International NAVTEX Service messages on 518 kHz shall be broadcast only in English in accordance with resolutions A.706(17), as amended, and A.1051(27), as amended

8.2 There is often a requirement for NAVTEX broadcasts to be made in national languages in addition to English. This shall only be achieved by the provision of a National NAVTEX service. National NAVTEX services use frequencies other than 518 kHz, and languages as decided by the Administrations concerned. These National NAVTEX services may be broadcast on 490 kHz or 4209.5 kHz, or on an alternative nationally assigned frequency.

9 Information control

9.1 The time-shared nature of NAVTEX services imposes the need for strict discipline in controlling the information flow of the broadcast. To achieve this, it is necessary to coordinate the messages in each B₂ category at each transmitter. In general, all messages shall be brief and clear and avoid duplication. Strict adherence to relevant guidelines in resolutions A.706(17), as amended, A.1051(27), as amended, and the Joint IMO/IHO/WMO Manual on Maritime Safety Information is recommended.

9.2 In addition, certain operating procedures have also been found necessary:

.1 messages in each category should be broadcast in reverse order of receipt by the NAVTEX Coordinator, with the latest being broadcast first; and
.2 cancellation messages should be broadcast once only. The cancelled message should not be transmitted on the broadcast in which its cancellation message appears.

10 Message content

10.1 It is important that national Administrations operating or planning NAVTEX services are clear about what sort of information should be included in the messages.

10.2 The International NAVTEX service should be used for transmitting maritime safety information only and should not be used as a medium for providing Notices to Mariners or for broadcasting Local Warnings. NAVTEX is essentially a medium for broadcasting information that is needed by ships to safely navigate through the NAVTEX service area of the appropriate NAVTEX station, particularly those ships on coastal passages. More detailed guidance in respect to different classes of messages is given below. Examples of the content and layout of NAVTEX messages are shown in the Joint IMO/IHO/WMO Manual on Maritime Safety Information. This publication should be available to all personnel responsible for the drafting of messages to be broadcast by NAVTEX stations.

10.2.1 Navigational warnings

.1 coastal warnings and NAVAREA warnings (B₂ = A or L) issued under the guidance of resolution A.706(17), as amended, which would be of concern to ships in the NAVTEX service area allocated to the transmitter should be included in the broadcast. Relevant coastal warnings should normally be repeated at every scheduled transmission for as long as they remain in force; however, if they are readily available to mariners by other official means, for example in Notices to Mariners, then after a period of six weeks they may no longer be broadcast. NAVTEX Coordinators should arrange to receive NAVAREA warnings appropriate to their area for inclusion in their broadcasts. These should be broadcast at least twice each day – to avoid overloading the broadcast time slot, they should normally be scheduled for transmission during slots that do not include weather forecasts (see 12.4);
.2 in-force bulletins (a summary of navigational warnings in force) should normally be broadcast each week; and
.3 local warnings should not be broadcast on International NAVTEX, i.e. information relating to inshore waters, often within the limits of jurisdiction of a harbour or port authority.

10.2.2 Meteorological warnings and forecasts

.1 meteorological warnings (B₂ = B), e.g. gale warnings, should be allocated a priority of IMPORTANT (see section 11) and be repeated at subsequent scheduled transmissions for as long as the warning is in force. These messages should contain only the appropriate warnings and should be separate from the weather forecasts;
.2 weather forecasts (B₂ = E) should be broadcast at least twice each day. This service should be carefully coordinated where transmitters are geographically close together;
.3 routine ice reports are normally broadcast on NAVTEX once a day; and
.4 ice accretion warnings (icing warnings) are normally included in gale warnings. If no gale warning is issued, they are to be treated as a meteorological warning (see 10.2.2.1).

10.2.3 Search and rescue information

.1 the NAVTEX broadcast is not suitable for distress traffic. Therefore, only the initial distress message should be retransmitted on NAVTEX, using B₂ = D, in order to alert mariners to a distress situation, by setting off an audio alarm.
.2 a single authority, which will normally be a Rescue Coordination Centre (RCC), should be designated SAR Coordinator to input information via the NAVTEX Coordinator, for a NAVTEX message. The initial shore-to-ship distress-related message should have previously been broadcast on the appropriate distress frequency prior to any related NAVTEX message being broadcast.

10.2.4 Piracy warnings

Piracy warnings should be transmitted using B₂ = D, in order to alert mariners by setting off an audio alarm. They should be broadcast immediately on receipt and at subsequent scheduled transmissions.

10.2.5 Tsunamis and other natural phenomena warnings

Tsunami, negative tidal surge warnings should be transmitted using B₂ = D, in order to alert mariners by setting off an audio alarm. They should be broadcast immediately on receipt and at subsequent scheduled transmissions.

10.2.6 Pilot and VTS service messages

Technical subject indicator character, B₂ = F, is only to be used for broadcasting temporary alterations, movement or suspension to pilot or VTS services. This category is for the information of all ships and is not to be used for specific instructions to individual ships or pilots.

10.2.7 No messages on hand

When there are no NAVTEX messages to be disseminated at a scheduled broadcast time, a brief message should be transmitted to advise the mariner that there is no message traffic on hand. Technical subject indicator character, B₂ = Z, is to be used to announce "NO MESSAGES ON HAND".

10.2.8 Use of abbreviations

Common examples of abbreviations used in the International NAVTEX service are contained in the Joint IMO/IHO/WMO Manual on Maritime Safety Information.

10.2.9 National NAVTEX services

Transmissions on 490 kHz or 4209.5 kHz may simply repeat the messages broadcast over the International NAVTEX service but in a national language, or they may be tailored to meet particular national requirements, for example by providing different or additional information to that broadcast on the International NAVTEX service, targeted at recreational vessels or fishing fleets.

11 Message priorities and broadcast procedures in the International NAVTEX service

11.1 Message priorities

11.1.1 The message originator is responsible for assessing the urgency of the information and inserting the appropriate priority marking. One of three message priorities is used to dictate the timing of the first broadcast of a new warning in the NAVTEX service. In descending order of urgency, they are:

VITAL
- for immediate broadcast, subject to avoiding interference to ongoing transmissions. Such messages should also be passed to the appropriate NAVAREA Coordinator for possible transmission as a NAVAREA warning via SafetyNET;
IMPORTANT
- for broadcast at the next available period when the frequency is unused; and
ROUTINE
- for broadcast at the next scheduled transmission.

11.1.2 Both VITAL and IMPORTANT messages should be repeated at each scheduled transmission time slot, if the situation is still valid.

11.1.3 The message priority is a procedural instruction for the NAVTEX Coordinator or the transmitting station and should not be included in the message. By selecting the appropriate priority of VITAL, IMPORTANT or ROUTINE at the transmission terminal, the message will be broadcast with the correct priority.

11.1.4 In order to avoid unnecessary disruption to the service, the priority marking VITAL is to be used only in cases of extreme urgency, i.e. to relay an initial shore-to-ship distress-related message or acts of piracy warnings, tsunamis and other natural phenomena warnings. In addition, VITAL messages are to be kept as brief as possible and in accordance with the Joint IMO/IHO/WMO Manual on Maritime Safety Information. The information provider is responsible for ensuring that the NAVTEX Coordinator is fully and immediately aware when a message should be broadcast with the priority of VITAL.

11.1.5 VITAL messages will normally be broadcast using NAVTEX number B₃B₄ = 00.

11.2 Broadcast procedures

.1 VITAL
- priority messages Messages assessed as VITAL are to be broadcast immediately, subject to avoiding interference to ongoing transmissions. On receipt of a message with a VITAL priority, the NAVTEX Coordinator will commence monitoring the NAVTEX frequency. If the frequency is clear, the VITAL message is to be transmitted immediately. If the frequency is in use, the Coordinator should contact the station which, according to the schedule, will be transmitting during the following time slot and ask it to postpone their transmission start by one minute, to allow a space for the VITAL message. Once the VITAL message has been transmitted, the scheduled station is free to start its routine transmissions;
.2 IMPORTANT
- priority messages Messages assessed as IMPORTANT are to be broadcast during the next available period when the NAVTEX frequency is unused. This is to be identified by monitoring the frequency. It is expected that this level of priority will be sufficient for the majority of urgent information; and
.3 ROUTINE
- priority messages Messages assessed as ROUTINE, are to be broadcast at the next scheduled transmission time. This level of priority will be appropriate for almost all messages broadcast on NAVTEX and is always to be used unless special circumstances dictate the use of the procedures for an IMPORTANT or VITAL priority message.

11.3 Meteorological NAVTEX messages

The following priorities are to be assigned to meteorological NAVTEX messages:

.1 Tsunami warnings = VITAL
.2 Meteorological warnings = IMPORTANT
.3 Meteorological forecasts = ROUTINE
.4 For other natural phenomena warnings, either VITAL or IMPORTANT may be used.

11.4 National NAVTEX services

The broadcast procedures concerning differing message priorities are the same for both the International and National NAVTEX services.

12 Responsibilities of a NAVTEX Coordinator

12.1 The NAVTEX Coordinator is responsible for the messages transmitted by each station under their control. This responsibility includes checking that the content of each message is in accordance with the Joint IMO/IHO/WMO Manual on Maritime Safety Information and also, that it is relevant to the NAVTEX service area of the transmitting station. Thus a user may choose to accept messages, as appropriate, either from the single transmitter which serves the sea area around their position or from a number of transmitters. Ideally, the user should select the station within whose coverage area their vessel is currently operating and the station into whose coverage area their vessel will transit next.

12.2 The NAVTEX Coordinator must:

.1 act as the central point of contact on matters relating to NAVTEX transmissions for a given transmitter or number of transmitters;
.2 be responsible for continuously ensuring quality control for the operation of the NAVTEX transmitting stations under its jurisdiction. This should be achieved with the cooperation of the information providers to ensure that:
- .2.1 messages are always concise and can be transmitted within the designated 10-minute time slots assigned by the IMO NAVTEX Coordinating Panel;
- .2.2 MINIMUM power is used to achieve satisfactory range performance; and
- .2.3 the coordinated service is operating satisfactorily;
.3 assess all requests for NAVTEX messages immediately upon receipt;
.4 schedule each message for broadcast in accordance with the priority of VITAL, IMPORTANT or ROUTINE;
.5 monitor the International NAVTEX frequency along with any other National frequency used by the transmitters under their jurisdiction in order to ensure that the messages have been correctly broadcast;
.6 monitor the International NAVTEX frequency along with any other National frequency used in order to identify vacant transmission periods required for VITAL or IMPORTANT messages;
.7 pass all information which warrants promulgation outside of their NAVTEX service area directly to the appropriate authority, using the quickest possible means;
.8 allocate a message identity to each message, including the sequential NAVTEX number;
.9 ensure that NAVTEX messages which have been cancelled are removed from the broadcast schedule at the same time as the cancellation message is promulgated;
.10 broadcast in-force bulletins not less than once per week at a regular scheduled time;
.11 promote and oversee the use of established international standards and practices with respect to the format and protocols associated with NAVTEX messages;
.12 maintain records of source data relating to NAVTEX messages in accordance with the requirement of the national Administration;
.13 be aware of the responsibilities of a NAVAREA, Sub-area and National Coordinator contained in resolution A.706(17), as amended, paying particular attention to the specific guidance for the promulgation of internationally coordinated maritime safety information provided therein;
.14 be aware of the responsibilities of a METAREA Coordinator contained in resolution A.1051(27), paying particular attention to the specific guidance for the promulgation of internationally coordinated maritime safety information provided therein; and
.15 take into account the need for contingency planning.

12.3 Management of the service

Data priority:

Most information broadcast on NAVTEX services relates to either navigational warnings or meteorological information. These types of information often originate from different organizations within a country and it is not until they arrive with the NAVTEX Coordinator that an assessment can be made as to whether there is too much information for the relevant broadcast time slot. Each data provider may consider their data to be more important and therefore, require transmission in full. However, the NAVTEX Coordinator needs to control the overall volume of data broadcast and may need to refer back to data providers to prioritize their information and reduce the amount of data to be broadcast. Some NAVTEX Coordinators utilize digital systems which include software that provides a readout of predicted transmission times for data held ready for broadcast. This enables the Coordinator to anticipate any problems and take action before the scheduled broadcast.

Data to meet purely national requirements should not be broadcast on the International NAVTEX service, but should be migrated to a National NAVTEX service (see section 14).

12.4 Balancing the volume of data to be broadcast throughout the daily transmission cycle

12.4.1 For many categories of messages there is no option with regard to when they should be transmitted. However, in order to minimize the risk of over-running the allocated 10-minute time slot, it is possible to balance the overall length of transmissions by broadcasting NAVAREA warnings at different times from weather forecasts and the in-force bulletin. An example of how this may be managed is given below for a station with a B₁ transmitter identification character C:

Time slot	Content
0020-0030	coastal warnings NAVAREA warnings
0420-0430	coastal warnings in-force bulletin
0820-0830	coastal warnings weather forecasts
1220-1230	coastal warnings NAVAREA warnings
1620-1630	coastal warnings ice reports
2020-2030	coastal warnings weather forecasts

13 Best practice for those using the service

13.1 In order to ensure that all necessary maritime safety information has been received, it is recommended that the NAVTEX receiver is switched on at least 12 hours before sailing, or preferably left on at all times.

13.2 Logging

13.2.1 The reception of navigational warnings or meteorological information on NAVTEX does not need to be noted in the radio log; the NAVTEX printout (or the non-volatile message memory) satisfies the requirements of regulation 17 of chapter IV of the 1974 SOLAS Convention, as amended.

14 Mutual interference between NAVTEX stations

14.1 The two principal causes of interference are:

.1 transmission overruns; and
.2 excessive power output.

14.2 Although NAVTEX continues to be generally reliable and an effective medium for the promulgation of maritime safety information, the worldwide infrastructure continues to expand and the volume of information that each Administration disseminates through the International NAVTEX service continues to increase. There is a danger that in some geographical areas, without firm management, both the system and system users may become overloaded with information on the single frequency used. This is of particular importance when handling messages of VITAL priority.

14.3 Many stations are filling their allotted 10-minute time slots and an increasing number are over-running. Instances of interference with neighbouring stations, as a result of over-running the time allocation, are also increasing. Where adjacent stations have transmitter identification characters which follow alphabetically (i.e. adjacent time slots), if the first station over-runs, it may mask the phasing signal of the second station such that, to the user, it seems as if the second station is off the air. Maritime safety information from the second station, although broadcast, may not be received by the system users. Over-run is usually caused by one or more of the following which must be avoided preferably by controlling the volume of data broadcast:

.1 a significant increase in safety-critical activity such as cable laying. Navigational warnings promulgating such activity often include numerous waypoints which are listed by Latitude and Longitude;
.2 meteorological information provided in a manner which is not concise and easily assimilated by the system user or for a much wider area than is covered by the NAVTEX station; and
.3 additional information provided for non-SOLAS system users, e.g. longer-range weather forecasts for fishing and recreational vessels.

15 Notification of NAVTEX services

15.1 National Administrations should ensure that mariners are informed of the establishment of, and/or changes to, NAVTEX services by inclusion of full details in Notices to Mariners and lists of radio signals. In addition, full details should be forwarded to the appropriate NAVAREA Coordinator, METAREA Coordinator and:

International Maritime Organization
4 Albert Embankment London SE1 7SR
United Kingdom
Telephone: +44 (0)20 7735 7611
Telefax: +44 (0)20 7587 3210
Email: ncsr@imo.org (in subject line add: for Chair, IMO NAVTEX Coordinating Panel)

International Telecommunication Union
Radio communication Bureau
Place des Nations
1211 Genève 20
Switzerland
Telephone: +41 22 7305560
Telefax: +41 22 7305785
E-mail: brmail@itu.int