Class B AIS

Class B AIS Information Page

Class B AIS Information Page


In this article I will be taking a closer look into how a Class B AIS operates, The difference in performance to a Class A AIS and how a Class B AIS could the perfect fit for your vessel.

Any vessel that has a Class B AIS installed has one installed due to the fact it provides so many added feature that help you see and be seen by other vessels.

A Class B transponder continuously receives information form all Class A and Class B AIS equipped vessels around you.  At the same time your Class B will transmit your position to all AIS equipped vessels automatically. 

Benefits Of Having An AIS

• Safety at night and in poor weather conditions
The class B AIS is a vital navigation tool in poor visibility conditions. The information received from other AIS ‘targets’ provides the user with vital navigation information and the position transmission alerts other vessels to the users location. However this should not be the only tool used for navigation as not all vessels have an AIS installed on their vessel.
• Combined with radar, AIS gives you the best possible picture of your situation in all conditions
• Safety in high traffic / commercial shipping areas
• Position transmission to authorities / nearby vessels in case of emergency
Certain SART transmits on the VHF band which will be picked up and displayed on your equipment connected with AIS such as your Radar or Chart Plotter.
• Best possible picture of a dynamic environment (moving vessels)
• Graphically view your position in relation to other vessels when connected to suitable display
• Ability to ‘see around the corner’ – vhf transmissions effectively make it possible to see around a headland, bend on a river or island
• Positively identify the identity of a target with name, callsign and MMSI number – then easily establish VHF voice contact or initiate a DSC VHF call

ais transceiver information help

Data That A Class B AIS Transmits

AIS transponders keeps transmitting information even when the subject vessel is anchored. The information contained in each AIS-data packet (or message) can be divided into the following two main categories:

Dynamic Information:

Maritime Mobile Service Identity number (MMSI) – a unique identification number for each vessel station (the vessel’s flag can also be deducted from it)
Speed over Ground – 0 to 102 knots (0.1-knot resolution)
Position Coordinates (latitude/longitude) – up to 0.0001 minutes accuracy)
Heading – 0 to 359 degrees
UTC seconds – the seconds field of the UTC time when the subject data-packet was generated.

Static & Voyage related Information:

Call Sign – international radio call sign assigned to the vessel by her country of registry.

Name – up to 20 characters

Type (or cargo type) – the AIS ID of the subject vessel’s shiptype   

Dimensions – approximated to the nearest metre (based on the position of the AIS Station on the vessel)    

This information is transmitted every 30 seconds while the vessel is undergo and every 3 minutes while at anchor.

A new AIS application is vessel tracking, with websites like Marine Traffic that collect and display thousands of AIS targets from their shore based AIS reception networks, and global satellite reception via companies such as Orbcomm, exactEarth and Spacequest.

Class B AIS Data Interfacing Capabilities

Class B AIS Data Interfacing Capabilities

AIS has the ability to transmit its data into other equipment on board such as a Chart Plotter, Radar, ECDIS etc, using NMEA 0183 or NMEA 2000.  This data will appear though the header sentences VDO and VDA. This data will display vessel position on connected devices such as Radar or Chart Plotters.  This allows you to obtain a more detailed picture of your surroundings.   Some Class B AIS are able to produce a source of Position data via NMEA 0183 or NMEA 2000.  This information is provided through the header sentences GLL, GGA and ZDA.  Allowing your Class B AIS to become a vocal point of your vessel data network. 

A VHF splitter can be installed which will allow your VHF and AIS to operate off the same VHF antenna. Combining your VHF and AIS to operate off the same antenna does not affect the proformence.  While at the same time reduceing the space taken up on your mast and integrates your AIS into your vessels wiring network further. This shows that a device that is not required at all, can quickly become the backbone of a ships wiring layout.