NAVTEX On Ships

  • Aviinash 
  • 4 min read

NAVTEX is abbreviated as Navigation Text Messages. It is used in ships to provide short range safety information that includes metrological warnings, weather forecasts and other messages that will provide safety to the crew of the ship. It was invented to provide a simple and automated means of receiving information in ships. It will cover a range of about 200 nautical miles and it will vary depends on device. Ships of any size can use this device. The International Convention for the Safety of Life at Sea (SOLAS) has made a rule to carry this device in ships from August 1, 1993. The information using this device are transmitted to ships by Navy or Coast guard or National Navigation Authority at free of cost.

NAVTEX
Image Credit: Wikipedia

Principle

It uses the mechanism of Radioteletype (RTTY) to send text messages and they are expressed in 7- unit code. The message will consists of 9 characters and these characters are used to identify the station and type of message.

How Are NAVTEX Areas Identified ?

For this purpose, they have divided the world into 21 areas. Each area contains a NAVTEX stations and they has an identification code which are assigned to them from A to Z (Represent each country). The selection menu in NAVTEX receiver will helps the officer to determine from which station the information is to be transmitted to ships during emergency. On automatic selection, the device will receive the information automatically based on the location of it. On manual selection, they can decide from where want to receive information. Each stations are allotted with a time slot of 10 minutes and this slots are repeated every 4 hours. Within this time limit all the information are conveyed from stations to officer of ship.

Use of NAVTEX Receiver :-

NAVTEX is a device which will provide additional safety to the on-board officers and staffs. It helps in providing navigational warnings, weather forecasts and other information in a particular range. It helps the crew in the ship to have their journey safely. It is user friendly as it will receive message automatically when information transmitted to ships from NAVTEX stations. This also helps officer to avoid distractions during the journey. By this, the officer will be aware of excepted weather and can plan accordingly. 

How To Read NAVTEX Messages ?

These are the following messages that will be received on NAVTEX:

  • A= Warning related to navigation
  • B= warning related to weather
  • C= report on ice
  • D= Information on search and rescue
  • E= Weather forecast
  • F= Messages to pilot
  • G= AIS messages (formerly Decca messages)
  • H= Loran C messages
  • I= Omega messages
  • J= Satnav messages (GPS) 
  • K= other navigational messages on electronic aid systems
  • L= warnings on navigational (additional)
  • M to U= Reserve
  • V= Fisherman notice
  • W to Y= Reserve
  • Z= No messages on hand

The officers will reject some of the messages. However some of the messages like A, B, D and L cannot be rejected as they are important for the officers to take decisions accordingly. 

The message that will be received on NAVTEX device will be in the following format:

  1. ZCZC   b1 b2 b3 b4     MAIN MESSAGE     NNNN
  2. ZCZC: It indicates the start of the message
  3. B1: This will represent the ID of the NAVTEX station.
  4. B2: This will represent the message from the above characters A to Z. 
  5. B1 and B2 are used by the officers to reject certain messages. 
  6. B3 and B4: They are two digit serial numbers assigned to each message. 
  7. B3 and B4 are used by the officers to find the messages that are being repeated. 
  8. NNNN: It indicates the end of the message. 

What is the Transmitting Range of Most NAVTEX Stations ?

The device typically have a range of 200-400 nautical miles. The range will depends on how much area that device was assigned to send messages. The NAVTEX broadcasts will achieve maximum transmitting range in the middle of the night. The frequency that are assigned to this device is 518 KHz and 490 or 4209.5 KHz. The communication of international NAVTEX stations will be in English and it will have a frequency of 518 KHz. For national transmission of NAVTEX, it will use a frequency of 490 KHz and it will be in local language.

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