Frequently Asked Questions

1. What actually is AIS?
2. How does AIS work?
3. For AIS you need a transponder. What is that?
4. Is an AIS transponder all I need?

5. What does AIS actually cost?
6. Is AIS advantageous for
inland shipping entrepreneurs?

7. Who else benefits from AIS?
8. Can I use AIS to navigate?

9. If I use AIS, can anyone track me?
10. Is the use of AIS mandatory?
11. Can I use virtually any AIS device?
12. Can I currently use AIS throughout Flanders?
13. Class A vs. Class B transponders?

1 What actually is AIS?

AIS stands for Automatic Identification System. It is an identification system that automatically transmits information about the name, position, speed and course of a ship. AIS has been in use for a long time in maritime shipping. To better respond to the specific needs of inland shipping, an Inland AIS has been developed.

If your ship is equipped with AIS, data is automatically sent to shore-based installations called AIS base stations. Bridges and locks, for example, receive data on your expected time of arrival. Via AIS, shore-based receiving stations can automatically send you short safety messages such as extreme weather warnings. Water levels can also be transmitted via AIS. The receiving stations are managed by competent local authorities.

Through AIS you can even automatically exchange data with other vessels in the vicinity – as long as they are also equipped with AIS. If you link AIS to the radar or electronic navigational chart, you can see all ships nearby, including their name, position and speed. Your on-board computer screen will always give you a complete display of the current traffic situation on the fairway. In this way AIS supports and facilitates navigation.

to top

2 How does AIS work?

AIS uses radio technology. Via radio signals AIS transponders transmit messages to each other and to shore-based receiving stations. This happens automatically and periodically, with short or longer intervals. A fast-moving vessel will transmit AIS messages at shorter intervals than a ship that is travelling slower or is moored. Two special VHF channels are reserved for AIS data traffic.

Certain hardware and software is needed for AIS. The hardware is a black ‘box’ with built-in GPS. The software ensures that (standard) messages are broadcast.

The information in these messages include: the MMSI number, the dimensions, position and name of the ship, ‘blue sign’ and cones, place of departure, destination, expected time of arrival (ETA) etc. Only the MMSI number and position are automatically broadcast. This is a unique nine-digit number that identifies the AIS unit.

The inland shipping entrepreneur himself decides what other information to add to messages transmitted via AIS. Protocol 24 of the CCR states that static and dynamic data – such as vessel size, antenna position and cargo information – should be inputted in a competent manner.

to top

3 For AIS you need a transponder. What is that?

This term is a contraction of the words transmitter and responder. A transponder is an electronic device with a built-in GPS that automatically sends and receives messages. Transponders are used in various forms of electronic communication, including aviation, satellite television and road traffic, where buses may have a transponder on board to change traffic lights to green.

4 Is an AIS transponder all I need?

Yes and no. A free-standing AIS transponder installed in the wheelhouse does work, but you can’t do much with it. Your transponder certainly has a small keyboard and display, but you can really only use them to input your own data.

AIS is only really useful when you can see information on other vessels on the chart. Therefore we strongly recommend you integrate the AIS transponder with the electronic navigational charts (Inland ECDIS charts) installed on your computer, and possibly also integrate it with the radar, via a ‘radar overlay’. This allows the chart to display ships which also have AIS on board. You immediately see all the information contained in the AIS messages with regard to these ships: name, position, size, speed, course, etc.

Modern radar systems and electronic navigational charts (Inland ECDIS) are supplied ready to be integrated with AIS. The latest systems (radar overlay) even integrate the electronic chart image with the radar display. This has the advantage that the other ships are visible on the electronic chart. The ‘level’ with AIS information – name, position, speed, etc. – is thus overlaid.

to top

5 What does AIS actually cost?

The prices of the AIS devices have decreased dramatically in recent months. The prices vary from manufacturer to manufacturer and from installer to installer. Today, a good recommended price is approximately 2100 euro.

Optionally you can also purchase AIS software, if you want to integrate AIS with your PC and your digital navigational charts. This software costs between 250 and 400 euros. This does not include the price of Inland ECDIS charts. Integrating AIS into your radar (the so-called radar overlay system) will cost between 6700 and 6900 euros.

6 Is AIS advantageous for inland shipping entrepreneurs?

Certainly. As an inland shipping entrepreneur with AIS you can more easily identify nearby ships. At a glance you can see the name, speed and course of crossing and oncoming ships. For example if you want to make passing arrangements, you can call a ship directly by name. Because your ship is continuously and automatically transmitting basic information about your name and position, you do not have to use the maritime radio to report to every post. That significantly reduces maritime radio traffic.
As AIS has a longer range than radar, you can also look further ahead. You can look ‘around the corner’ of bends and obstructions such as bridges and tall buildings. Beware: AIS is a complement to the radar; it does not replace it!

to top


7 Who else benefits from AIS?

AIS is also interesting for traffic posts and port authorities. They get a clear picture of the traffic demand and traffic levels, so can better monitor and manage inland shipping. For example, traffic management improves forward planning at locks and enhances efficiency at moorings. In addition, the use of movable bridges can be better aligned with waterway traffic. AIS also improves traffic safety. Interventions at collisions and other incidents can be implemented more quickly. With AIS, ships no longer remain anonymous to the emergency services during calamities.

For inland shipping companies AIS is also interesting. AIS provides them with enhanced tracking information on where a shipment is in transit. If the ship owner and the shipping company come to an understanding about this, the shipping company can better plan its activities and closely monitor the ongoing voyages.

8 Can I use AIS to navigate?

No. The radar remains the most reliable navigation system. AIS is an additional source of information that complements and supports the radar, but never replaces it.

Radar detects everything and does not depend on another ship’s AIS. Basically AIS only recognises another ship if that ship is also using AIS. By itself AIS is not sufficient for safe navigation. As every vessel is not (yet) equipped with AIS, there will always be shipping traffic that is not covered by AIS. So you can not trust it blindly.

Consequently, in the wheelhouse the radar screen retains its central role. AIS can definitely be used to supplement the information provided by the radar. Information from the AIS can then be merged with the radar information on the radar screen.

to top

9 If I use AIS, can anyone track me?

It’s not easy to answer this question. Of course, you can be seen by all other ships equipped with AIS. The situation is even more complicated on shore. The receiving stations which are currently installed in Flanders are managed by the Shipping Assistance Division of the Agency for Maritime Services and Coast (MDK), an agency of the Flemish government. The shipping guidance decree states that AIS data received by that department can be made available to other governments. This already happens today, for example with the harbourmaster’s services. According to the regulations data may also be exchanged with a commercial party, provided that the vessel is owned by that party or is sailing in its service. Currently that information exchange does not take place.

In the coming years more AIS receiving stations are to be installed along the Flemish waterways. Very likely they will come under the jurisdiction of the waterway management authorities. Whether and how they will exchange AIS information with commercial partners is not yet known. In any case, on the basis of the RIS decree they must ensure the stipulated degree of privacy.

A separate problem is the listening stations. These are stations that are able to receive AIS messages, but in contrast to receiving stations are not able to broadcast information back to the ship. These listening stations are usually installed and operated by commercial companies. Therefore they do not need a licence. They certainly do not have the right to receive radio communications intended for third parties (Article 41 2 ° of the Law of 13 June 2005 on electronic communications). Under Belgian law, these commercial parties must not receive AIS messages and certainly not spread them without the consent of the ship. Unfortunately, this does occur in practice today.

to top

10 Is the use of AIS mandatory?

In various member states of the European Union, the preparations for an AIS mandate are under way. In Belgium, the Antwerp Harbour introduced the AIS mandate on 01 January 2012. The use of AIS is already obligatory on portions of the Danube in Austria and Hungary.

11 Can I use virtually any AIS device?

No. Since 1 April 2008 only AIS devices that fulfil the test standard can be built-in. The installers must also be recognised by a competent authority. You can find a list of approved devices and installers here.

The Central Commission for Navigation on the Rhine (CCR) has established criteria for the use of AIS devices. For example, the AIS unit must be installed in the wheelhouse, it must be mandatorily switched on and the ship’s data must be correctly entered. All these criteria are contained in Protocol 24 of the CCR.

12 Can I currently use AIS throughout Flanders?

Communication between ships equipped with AIS is possible anywhere. Information exchange between ship and shore is not yet possible. For this more AIS receiving stations are needed. As you can see on the chart, onshore AIS receiving stations currently ‘cover’ only the main routes in and around the ports of Zeebrugge, Ghent and Antwerp. The aim is to systematically expand coverage, so that by 2013 all the main fairways are ‘covered’.

to top

13. Class A vs. Class B transponders?

Class A AIS transponders (SOLAS Compliant) operate using Self-Organizing TDMA (SOTDMA) broadcast mode and transmit information every 2 to 10 seconds while underway (every 3 minutes while at anchor) at a power level of 12.5 watts. Static and voyage related vessel information, such as the vessel's name, are transmitted every 6 minutes. They are required to have a DSC (156.525 MHz) receiver, external GPS, heading, and rate of turn indicator. Class A units also transmit and receive safety-related text messages.

Class B AIS transponders operate using Carrier-Sense TDMA (CSTDMA) broadcast mode and transmit information every 30 to 180 seconds at a power level of 2 watts. Static data, such as the vessel's name, is transmitted every 6 minutes. A DSC receiver and heading are optional. Transmitting safety-related text messages is optional and they can only be pre-configured into Class B units.

The similarities and differences of Class A and Class B AIS are summarized in this table.

(table not available in other languages)

This website only conveys the opinion of the author.
Neither the European Union, or the partners of this portal
accept responsibility for any possible use
of the information on this site.