AIS stands for Automatic Identification System. In spanish, you could find a translation as SIA, meaning Sistema de Identificación Automática, (a more detailed explanation can be found on wikipedia here )


The main target of the AIS system is to allow ships to communicate its position and other relevant information so that other ships or land stations can know it.

The most important tool with AIS is actually collision avoidance, but has many other advantages that we will explain later on.

How was this communication done before?

Existing systems are radar, radio communication, sound alerts, visual alerts, and lately satellite communication.

We will explain later on all the differences among the different existing systems.

What you can do with AIS

- AIS A for large ships, already compulsory above 300Tn

- AIS B, specially adapted for small vessels, and very recently approved internationally.

- Land base stations

- Aids to Navigation (AtoN)

- Search and rescue aircraft AIS transponders.

Where is it compulsory

AIS was approved by the IMO in 2002, following an implementation calendar according to the boat’s characteristics, starting on December 31 of 2004. As for today, the following ships are obliged to carry AIS:

- Ships above 500 GT

- Ships on an international trip above 300 GT

- All passenger ships, regardless of its size
A directive proposal will change the way it has been implemented in small boats ( 2002/59/E ), making it compulsory on fishing boats with the following implementation calendar:

  • fishing boats with length between 24 y 45 metres: no later than 3 years after the directive is approved;
  • fishing boats with length between 18 y 24 metres: no later than 4 years after the directive is approved;
  • fishing boats with length between 15 y 18 metres: no later than 5 years after the directive is approved;
  • newly built fishing boats, longer than 15 metres: no later than 18 months after directive is approved;

AIS for non-SOLAS non-fishing boats. We mean leisure craft:

Commision decision, on January 25 of 2005, 2005/53/CE:
“Harmonization of radio services has contributed to increase security in non-SOLAS vessels, especially in dangerous situations, so member states invite such ships to participate on AIS”

This decision is thus a strong encouragement towards defining AIS as an essential tool in smallest boats.

The fact that DSC is compulsory since the start of 2008 in Spain is the first step towards the implementation of security measures such as AIS.

AIS compared to other aids to navigation


Radar uses a system that detects objects different than the sea itself, so it helps detecting ships, floating objets and of course earth. But it does not identify them, as AIS does. DARPA systems in radar let you nevertheless detect speeds and headings of objects moving. Other important differences are the far larger coverage offered by AIS, and far smaller energy consumption as well, so it is particularly adapted to small boats.

Since rocks and islands do not have AIS transponders (just yet) AIS and radar are complementary technologies. None of them substitutes the other.

Satellite communications

Ships can communicate through the Inmarsat system for example. It is possible to communicate ship’s location, like the blue box in EU ships. But it is not an efficient mean to send a ships location to the surrouding ships, since it would need a central system able to process all the information. Besides, that information sent via satellite on a regular basis would be nowadays very expensive. It is however possible to send AIS information via satellite.

Voice over VHF

Until today, when we saw a ship we only had a way to communicate to it, i.e., broadcasting a message through the radio, giving a description of the boat we want to talk to, and hope they would answer back.

AIS uses a data channel in VHF and facilitates communication among ships, since you can see MMSI, call sign and other identifications on your graphical display, and thus you can talk directly using those codes and your digital selective call, knowing also its precise location, name, heading, COG, and size. This means, no doubt a total new dimension in aids to navigation.

Sound and visual alerts

They are notably less useful than AIS, but still totally unparalelled in certain situations.