NavTex for Beginners: How Navigational Telex Works on Ships

by | Last updated Jan 30, 2024 | Equipment, Navigation | 0 comments

One of the navigational tools seafarers use to keep them updated with the latest maritime safety information is NavTex or Navigational Telex.

Even with ships using the internet and satellite communication, this equipment is vital on board and will still be in the future.

Due to its reliability, some manufacturers are now making paperless NavTex receivers and integrating them into the ECDIS System.

Key Takeaways

  • Navtex is an international system transmitting navigational and weather warnings to ships.
  • It operates on specific frequencies and relies on dedicated broadcasting stations.
  • With receiver screens of limited sizes, messages use coded formats with identifiers for efficient information delivery.

What is NavTex

Navigational Telex or NavTex is an international automated narrow-band direct-printing service used for disseminating maritime safety information.

It works on the medium frequency bandwidth of 518 KHz and 490 KHz, and a high frequency band of 4,209.5 KHz to deliver navigational and meteorological warnings, forecasts, and urgent messages to ships. 

Think of this as your fax machine that automatically prints safety messages upon reception.

How NavTex Works

Two underlying general services make Navtex work.

As you might have guessed, there must be a sender upon which this equipment gets their printouts.

These are the Information Services and the Broadcast Services. Take a look at the image below to see their functions.

A typical chart of service stations and broadcast stations working together to collect, process, and send messages.

Information Services

Information Services collect actual sources of navigational, meteorological, and safety-related maritime information (MSI).

The international and national MSI coordinators verify these details and sort them out to avoid duplication.

SAR information is also processed at this stage.

Broadcast Services

Broadcast Services involves the transmission of automated messages to vessels equipped with Navtex receivers.

They ensure critical information reaches mariners in a timely and standardized manner to the different NAVAREAS they are intended for.

Components of a Ship’s NavTex Receivers

A ship’s NavTex receiver may look like a simple navigational tool of 8” width and 5” height.

However, it consists of several key components designed to receive and process messages.

Here are the main components of a ship’s navigational telex receiver:

1. Antenna Unit – Captures signals transmitted by stations and sends them to the receiver unit for processing.

2. Receiver Unit – This unit is the core of the NavTex receiver. It is responsible for tuning into the specified frequencies, demodulating the received signals, and decoding the messages.

3. Control Unit – Provides the user interface for managing the NavTex receiver. It allows the crew to interact with the equipment such as setting preferences, selecting message types, and configuring the receiver settings.

3. Display Unit – Presents messages to the crew in a readable format. It may show information such as navigational warnings, weather forecasts, and other safety-related data.

The device should display at least 16 lines of message text and 32 characters per line per the IMO NavTex Manual.

4. Printer – Prints out received messages. Some modern units use a paperless system and don’t provide print options for messages.

6. Power Supply – Essential for the continuous operation of the NavTex receiver.

A digital navigational telex or NavTex showing a forecast for Yokohama NavTex Area.

NavTex Frequency Bands

NavTex is part of the Global Maritime Distress and Safety System or GMDSS that complies with the functional requirement of transmitting and receiving general radio communications.

Like any radio equipment, this equipment works on frequency bands of 518 KHz, 490 KHz, and 4,209.5 KHz.

518 KHz – This is the frequency band assigned for INTERNATIONAL NavTex service. Its range is up to 200 NM to 400 NM, perfect for use in Sea areas A1 and A2.

Furthermore, messages on this frequency broadcast only in English as per IMO  resolutions A.706(17), as amended, and A.1051(27), as amended.

490 KHz – This frequency is for NATIONAL NavTex services. Individual countries or administrations allocate this bandwidth for transmitting maritime safety information.

If you tune in to this frequency, you may receive messages in the local language besides English as determined by their government.

4,209.5 KHz – Like the 490 KHz, governments use this frequency for NATIONAL NavTex services.

They use this to accommodate the volume of information transmitted in addition to 490 kHz.

Note that these three are GMDSS frequencies.

Some countries may use different bandwidths for their national NavTex services besides those listed above.

NAVAREAS

NAVAREAs or Navigational Areas are geographic sea regions established by the International Maritime Organization to coordinate the broadcast of navigational warnings.

Since we can use NavTex anywhere in the ocean, we divided the seas into navigational areas to define maritime safety broadcasting.

21 NAVAREAs covering the world's seas and oceans

There are a total of 21 NAVAREAs worldwide.

These NAVAREAs cover different geographical regions and are designated by Roman numerals (I to XXI) to identify each area uniquely. 

As you can see above, each NAVAREA covers huge areas and may comprise different countries. They also have various broadcasting stations covering different parts of the NAVAREA.

Here is an image of the NAVTEX Coast Stations for NAVAREA I. Take note of the B1 Characters, as it will make sense later.

List of NavTex stations for Nav Area 1 in the 518 KHz.

NavTex Message

Messages received on a ship’s Navigational Telex may look weird to the untrained eye. With a screen size of about 6 inches, we have to send and receive messages efficiently.

Thus, every NavTex message, from navigational to SAR and LORAN messages, uses codes and identifiers to communicate crucial details to mariners.

Here is a sample NavTex message and the meaning of their symbols:

A sample of Navtex message with their parts.

Message Format

The standard format for NAVTEX messages has the same pattern as above. Here’s the format that it follows:

ZCZC

B1B2B3B4

Message

NNNN

Every Navtex message starts with ZCZC and ends with NNNN.

The coded parts, B1B2B3B4 are where we can identify the broadcasting station and the type of message we receive.

B1 – refers to the Transmitter Identification Character.

It indicates the transmitting station or the NAVTEX transmitter responsible for broadcasting the message.

B2 – refers to the Subject Indicator Character.

It indicates the subject matter of the message, such as navigational warnings, meteorological warnings, search and rescue information, ice reports, and other safety-related information.

B3B4 – is the Message Numbering Characters and are sequential numbers from 01 to 99.

We use this for organizing, identifying, and managing individual messages within the NAVTEX system.

Different subject line indicators alphabetically coded from A to Z with assigned message types.

Subject lines A, B, D, and L are in light brown highlight to emphasize that these indicators are mandatory and cannot be deselected on the NAVTEX receiver.

This ensures that ships using this equipment always receive the most vital information.

Next is the Message, which contains information about the subject lines that may be of interest to the seafarers.

May the winds be in your favor.

Gibi

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