AIS Automatic Identification System

AIS, Automatic Identification System, is an anti-collision and coordination system for maritime traffic.

The AIS system

AIS Automatic Identification System n.1

AIS, Automatic Identification System, allows you to monitor the position and other relevant information of boats in the vicinity equipped with AIS Transponder.

Normally chartplotters have the ability to process this data and therefore are able to represent on the chart the position of these vessels, along with other relevant information such as course, speed, name, MMSI, type, size and many more.

The frequency used is VHF and therefore the range is normally between 10 and 30 miles.

AIS models

AIS Automatic Identification System n.2


Two classes are currently in use:

  • Class "A" is intended for ships or fishing vessels that are required to do so (see section "The Regulations").
  • Class "B" is intended for recreational use, more limited in the power output, in the number of information (however abundant) and in the frequency with which it is transmitted.

Comparative Table Prerogatives and Information Class A / B

Class AClass B
Power TX12,5 W2 W
Data Frequency2 to 15 seconds30 seconds
Data frequency at anchor3 minutes3 minutes
SoG (Speed Over Ground)Yes.Yes.
Position ErrorYes.Yes.
Latidudine and LongitudeYes.Yes.
CoG (Course Over Ground)Yes.Yes.
True RouteYes.Yes.
Date/Time of informationYes.Yes.
Name of vesselYes.Yes.
Type of vessel Yes.Yes.
Dimensions of the vesselYes.Yes.
GPS position on the shipYes.Yes.
Type of differential receiver Yes.Yes.
Navigation Status Yes.No.
Rotation level and directionYes.No.
IMO NumberYes.No.
Radio Call SignYes.No.
Marine currentYes.No.
Destination nameYes.No.
Estimated time of arrivalYes.No.

AIS Active and Passive

There are models limited to reception only (passive AIS) and transponders (active AIS) capable of receiving and transmitting.

Passive AIS are therefore able to receive information from other vessels, but cannot transmit their own to the system. They cannot therefore inform others of their position and therefore the level of safety offered is much more limited: no one would drive a car with headlights off believing that the lights of other vehicles are sufficient ...

The Regulations

Ships subject to GMDSS


Fishing vessels

The legislative decree n.18 of 16/02/2011 establishes the obligatory nature of AIS class "A" on fishing vessels with an overall length greater than or equal to 15 metres, with the following implementation timetable:

  • From 24 to 45 meters: from 31/05/2012
  • From 18 to 24 meters: from 31/05/2013
  • From 15 to 18 meters: from 31/05/2014
  • Newly built vessels: before launching

(Length "from" means "above or equal to", length "a" means "below")


The use of passive or active AIS is optional when ordering. However, it is often required as a mandatory feature in many sailing regattas.
For use, as for marine VHF, is required the RTF License and the RTF Certificate and in the case of active AIS is necessary to request the MMSI code (without which the equipment can not transmit).