Class A AIS

What Is A Class A AIS

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What Is A Class A AIS

Introduction To Class A AIS

Within this page I will be discussing what a Class A AIS is, what the unit is capable of doing and the regulation effecting Class A AIS.  An AIS does not just list ships in the near by area anymore.  The unit has evolved to offer a multitude of different uses; from being used by Vessel Traffic Service (VTS) to interfacing into a wide range of electronic equipment on board.  An AIS also has a wide range of emergency features.  

Automatic Identification System (AIS) is an automated tracking system that displays other vessels in the vicinity. It is a broadcast transponder system which operates in the VHF mobile maritime band. Your own ship also shows on the screens of other vessels in the vicinity, provided your vessel is fitted with AIS. If AIS is not fitted or not switched on, there is no exchange of information on ships via AIS. The AIS on-board must be switched on at all times unless the Master deems that it must be turned off for security or any other reason. 

Collision Avoidance

The original idea for a Automatic Identification System first came about at the International Convention of SOLAS technical committee in ….  The concept was to create a piece of equipment to aid in the avoidance of collisions among large vessels at sea that are not within range of shore-based systems.

An AIS is capable of providing collision avoidance by factoring in the vessels; position, speed, heading destination and size.  An AIS then takes this data and calculates it route.  If the ship is to be crossing the route you are taking within a certain distance then the AIS will Alarm.  This is information is made much clearer when combined with a radar or ECDIS.

How Is AIS Data Intergrated Into Other Navigational Equipment

To aid in collision avoidance AIS data is capable of being overlayed onto various electronic devises including; Radar, ECDIS and Chart Plotters. This is achieved by either using NMEA 0183 or NMEA 2000.  The two header sentences that an AIS produces is VDM and VDO.  This overlay allows a vessel to obtain a much greater view and understanding of their surrounding.  This is due to the fact AIS overlay can easily identify if an echo on a Radar or ECDIS screen is a vessel or not.  Although AIS cannot be used as the only form of collision avoidance at sea due to only vessels over 300GT on international Voyages require an AIS to be fitted.  

Emergancy Features Of An AIS

AIS has come along way since it was brain stormed at the International Convention For Safety Of Life At Sea.  AIS now has a large array of safety feature inbuilt. They include: Closest Point of Approach, Emergency Text Messages on Channel 70 and AIS-SART.

Channel 70:                                                                                                                                                                                                                                                           An AIS is able to perform a DSC text message on channel 70 (156.525Mhz).  This means that in the event of an emergency the captain of the vessel is able to type out a message to send to all vessels within the immediate area.  This message can either be sent to all the vessels within the AIS range or it can be sent to a particular vessel depending on the reason for the message.

AIS-SART:                                                                                                                                                                                                                                                               The latest edition to the AIS emergency features is, the introductions of Automatic Identification System – Search And Rescue Transponders (AIS-SART) which came into effect in 2010.  Traditionally SART worked in-conjunction with radars. When the SART  is activated it automatically reacts to the emission of a radar. This in-turn enhances the visibility of the SART on a radar screen.  AIS-SART transmit a distress signal on the two AIS VHF frequencies (Channel 1: 161.975 MHz and Channel 2: 162.025 MHz).  This is then displayed on the AIS display and on any other connected screens such as a radar.  The edition of using the SART on the AIS band allows the SART to be displayed on multiple screens instead of just the radar screen.  This provides a more specific location of the SART. 

Closest Appoint Of Approach:                                                                                                                                                                                                Closest Point of Approach (CPA) The “Closest Point of Approach” refers to the positions at which two dynamically moving objects reach their closest possible distance. This is an important calculation for collision avoidance.  Within the marine industry and more importantly the for AIS, the two dynamically moving moving object is two vessels.  This will then make the AIS alarm informing the two vessels of a possible collision.  The captain of the vessel can then identify the other ship by the information provided from the AIS and make contact with each other through radio or other forms of communication. This is one of the most fundamental principles of AIS and it is clear why from this brief explanation.

What Are The Main Regulations Effecting Class A AIS

all vessels over 300 tons on international voyages, 500 tons non-international and all passenger ships


All class A AIS have met rigorous testing and safety standards.  A class A AIS is easy to identify by a official Wheel-Mark stick on the unit. Please see Image 1 for reference.  The Wheel-Mark indicates the compliance with Maritime Equipment Directive (MED). 

The MED EN came into force in 1999 and covers a range of equipment carried on board ships registered under the flags of the European Union Member States. It was established to ensure that equipment which must comply with the requirements of international conventions (e.g. SOLAS) agreed by the International Maritime Organisation also meets common standards of safety and performance across the EU. 

Approval requirements are also harmonised which ensures certificates issued in one Member State are accepted by all States across the EU. The Directive applies to all ‘Community Registered Ships’ and is mandatory from January 1, 2001.


The International Convention for the Safety of Life at Sea (SOLAS) is an international maritime treaty which sets minimum safety standards in the construction, equipment and operation of merchant ships. The convention requires signatory flag states to ensure that ships flagged by them comply with all regulation from SOLAS. Some flag stats may issue further requirements at their own choosing.  But all must meet the minimum set out by the SOLAS Convention.

The current version of SOLAS is the 1974 version, known as SOLAS 1974, which came into force on 25th May 1980. As of November 2018, SOLAS 1974 had 164 contracting states, which flag about 99% of merchant ships around the world in terms of gross tonnage.

SOLAS in its successive forms is generally regarded as the most important of all international treaties concerning the safety of merchant ships

Transmission Time

*AIS Transmits various Amounts of Information. One of the regulations on the AIS is that is transmits more data than a Class B and more frequently.  Below is a list of data a Class A AIS transmits

Dynamic Data – Dynamic Data is information that is constantly changing.  Therefore it needs to be continuously up to date.  The speed of the vessel effects how often this information is relayed. The Information is required to be transmitted so frequently so it can aid in collision avoidance which is mentioned further up the page

This Dynamic Data is transmitted every 2 to 10 seconds depending on the vessel’s speed and course while underway and every 6 minutes while anchored.

  • Position Time Stamp (UTC)
  • Course Over Ground
  •  MMSI Number
  • Ships Posisition
  • Heading
  • Rate Of Turn
  • Navigation Status

Static Data –  Static Data Consists of information about the vessel that is manually entered into the Class A AIS.  This data is transmitted every 6 minutes or when requested.  Please see the Static data for a Class A AIS below:   

  •  IMO Number
  • Name and Call Sign
  • length and Beam
  •  Type of Ship/Cargo
  • Location of mounted fixings
  • Ships Draught
  •  Destination and ETA
  • Route Plan (Way Points)

For everything else AIS.  Please go back to our HUB Page for more information.