Working, types of messages and advantages for Navtex

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Types of messages and advantages for Navigation Telex
Types of messages and advantages for Navigation Telex

It is of utmost importance that every navigating officer ensures the safety of the vessel and its crew. Accidents can happen to the most cautious and prudent of navigator. Right from the start of voyage planning, the navigator needs up to date information that will affect the passage of the ship. The most important information to vessels is information related to safety including Maritime Safety Information.

Maritime Safety Information includes navigational and meteorological warnings, meteorological forecasts, warnings about dangers to navigation, warnings of missing vessels and other urgent messages pertaining to safety of the vessel and its crew. Constant monitoring to pick up wanted information among a vast volume of messages is not very practical with a limited radio system. The NAVTEX system provides all navigating officers with up to the minute information automatically.

NAVTEX, an acronym for navigational telex (navigational text messages) is a device used on-board the vessels to provide short range Maritime Safety Information in coastal waters automatically. It can be used in ships of all types and sizes. The area covered by Navtex can extend as far as 400 nautical miles from the broadcast station. A NAVTEX receiver on board prints out navigational and meteorological warnings and forecasts as well as urgent Marine Safety Information to ships. It forms a vital element of the Global Maritime Distress Safety System (GMDSS). Navtex uses the feature of radio telex or Narrow Band Direct Printing (NBDP) for the automatic broadcast of information.

HOW A NAVTEX WORKS?

The Navtex works on a frequency of 518 kHz in the medium frequency band. 490 kHz frequency is also used by some countries for broadcasts in the national languages, also known as national navtex. Where medium frequency reception is difficult, transmissions are made on 4209.5 kHz. The default setting in a Navtex is 518 kHz. The entire world is divided into 21 areas known as NAVAREAS (including 5 areas recently introduced for the Arctic region) for the purpose of distributing these information. Each Navarea has multiple navtex stations which further helps in transmitting the messages.

SELECTION OF STATIONS

All navtex receivers are programmable to enable the navigating officer to ensure that only messages from selected Navtex Stations are displayed or printed. The SELECTING STATION menu under the Menu option in a Navtex Receiver allows the officer to select the desired stations he/she wants to receive automatically or manually. On automatic selection, the navtex receives Marine Safety Information for the area the ship happens to be in continuously and without any user involvement. If ship’s position data is fed from any navigating equipment like GPS, the Navtex will automatically decide in which NAVAREA the ship is navigating presently and thus select the appropriate Navtex Stations. In the manual mode, the navigating officer can select what stations he/she wishes to receive. A list of Navtex Stations can be found in the Admiralty List of Radio Signals Volume 3 Part 1 and in the List of Coast Stations and Special Service Stations (List IV) for reference.

TYPES OF MESSAGES

The Navtex receives the following kind of messages :

A = Navigational Warning

B = Meteorological Warning

C = Ice report

D = Search and Rescue Information/ piracy and armed robbery

E = Meteorological forecast

F = Pilot messages

G = AIS messages(formerly Decca messages)

H = Loran C messages

I = Omega messages

J = Satnav messages (GPS or GLONASS)

K = Other electronic navigational aid system messages

L = navigational warnings (additional)

M to U = Reserve

V = Notice to fisherman

W to Y = Reserve

Z = No messages on hand

The navtex receiver can be set to ignore certain types of messages, however, messages A,B,D and L because of their importance cannot be rejected by navigating officers. Audible alarms can also be generated when message type A,B,D or L is received. It should only be possible to reset this alarm manually. We should also note that when programming the type of messages to receive, it is wise to ensure that only those which are required and necessary are programmed for reception. Otherwise a good deal of paper will be wasted or one will have to scroll through a mass of messages if the broadcasts are received in soft copy.

Navtex Push To Open
Navtex Push To Open

THE FORMAT OF THE MESSAGE

The message in a Navtex Receiver appears in the following format :

ZCZC   b1 b2 b3 b4     MAIN MESSAGE     NNNN

ZCZC : It is the start code. It indicates the beginning of the message.

B1 : This character represents the Station ID.

B2 : This character is called the Subject Indicator. It is used to represent the type of message. (A to Z)

The characters B1 and B2 are used by the navtex receivers to reject messages from stations of concerning subjects of no interest to the officer.

B3 and B4 : B3 and B4 is a 2 digit serial number for each message.

NNNN: This indicates the end of message.

The characters B3 and B4 are used by receivers to keep already received message from being repeated.

Below is an example of a message :

ZCZC OA20

WZ 1593

Scotland, West Coast

The North cardinal light buoy 58.01.2N 005.27.1W

have been permanently withdrawn.

Cancel WZ 1562

NNNN

Every Navtex message has information within the message header. In the above message :

The letter “O” indicates a broadcast from the Navtex station, here Portpatrick radio.

“A” indicates Navigational warning category message.

‘20’ indicates the navigational warning message priority sequence.

ADVANTAGES OF HAVING NAVTEX ONBOARD THE SHIPS :

Navtex is a form of extra insurance and an aid in peace of mind. It is a very convenient way of monitoring navigational warnings, meteorological warnings, search and rescue information and other data for ships sailing within 200 to 400 nautical miles off the coast. It thus provides pertinent navigational and weather related information in real time. As Navtex receiver receives messages automatically it is quite user friendly. An officer of the watch does not have to monitor it regularly or be physically present at fixed time. There is also no requirement for retuning of the receiver. This not only saves time but also stops an officer from being distracted on the bridge. With the information received from the Navtex receiver, passage plan can be amended as required for the safety of the vessel. An officer of the watch can attend to any distress warning in the vicinity. He is also aware of the expected weather and can plan accordingly. Thus a Navtex forms an integral part of the bridge navigational equipments.

NAVTEX RECEIVER CHECKLIST :

  1. Every officer should make sure that there are sufficient rolls of Navtex paper available on board at all times.

  2. It is important to check that there is paper in the receiver so that one does not miss out any important messages.

  3. It is advisable to leave the Navtex ON at all times to avoid the chance of loosing vital information that might affect the vessel during it’s voyage.

  4. Make sure that the operating manual is available on the bridge.

  5. A plastic copy of the NAVAREAs/METAREAs in which the vessel is likely to sail,showing the Navtex stations, their coverage ranges and their respective time schedules should be made available next to the equipment.

  6. A handy guide for programming, status and auto testing procedures can be made and kept with the equipment.

  7. Routine tests should be carried out to check the performance of the equipment.

  8. Extra care should be taken not to confuse the programming of B1 characters (station designators) with those of B2 characters (type of messages).

Related article : Navtex Type NX-300 Furuno

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