Select your product to confirm this information applies to you

Basics of AIS Transmission

A little history of AIS 

Automatic Identification System (AIS) uses a transponder or transceiver a GPS and VHF antenna. AIS improves maritime safety, aids in collision avoidance, and helps to identify ships that are not in sight. AIS transmits the ship's data to other vessels capable of receiving AIS data. The transponder sends the most important ship data, position, speed, and course; this system is used worldwide through standardized message types or telegrams. The data is transmitted twice in case of failure. The data sends over designated VHF Operating frequencies 161.975 MHz (channel A = 2087) and 162.025 MHz (channel B = 2088). There are 4500-time slots available per minute, 2250 per channel—the AIS transceivers alternate one message on channel A next on channel B. 


Garmin has transceivers (transmits and receives, also known as transponder) and AIS receivers. A Garmin AIS 800 is a Class B transponder. It sends vessel data and receives incoming data. Garmin also has VHF AIS radios that receive AIS data from ships with transponders. An AIS receiver helps the recreational user avoid larger vessels in heavily trafficked areas or dangerous areas. 

Transceivers

  • AIS 800 Blackbox 

  • AIS 600 Blackbox (discontinued)

Receivers

  • VHF 215 AIS Marine Radio

  • VHF 210 AIS Marine Radio

  • AIS 300 Blackbox (discontinued)


Types of AIS Service

There are two types of AIS service Class A and Class B. 

Class A Service for commercial vessels is required (transponders) 

Examples of standard ships required to have Class A service

  • Commercial Vessels 65 feet and longer

  • Towing vessels over 600 horsepower

  • Passenger vessels with more than 150 passengers

  • Dredges operating near a commercial channel

  • Cargo vessels carry specific types of dangerous materials

For the complete list of requirements for Class A, visit the US Coast Guard Navigation Center.

Class B Service

Pleasure boats are not required to carry AIS service. Class B is designed for smaller ships with fewer power options, less space, and fewer antennas than a commercial vessel. 


Operation

Class B Transmit Data

Dynamic Data 

  • Message number 18

  • MMSI number of vessel

  • Speed over ground

  • Position accuracy

  • longitude and latitude

  • COG (course over ground)

  • True heading

  • Timestamp

Class B Extended Position Report

Static Data

  • Message number 19

  • MMSI number of vessel

  • Speed over ground

  • Position accuracy

  • Longitude and latitude

  • COG (course over ground)

  • True heading

  • Timestamp

  • Ship's name (max characters 20)

  • Type of ship

  • Dimensions of the boat (to the nearest meter)

  • Type of positioning system (typically GPS or DGPS)


Class B Static Data Report

Message number 24

Message 24A: 

  • MMSI number of ship

  • Name of the ship (max 20 characters)

Message 24B: 

  • MMSI number of ship

  • Type of ship or pleasure boat

  • Vendor ID

  • Radio call sign

  • Dimensions of ship

Separated in two messages 24A and 24B, sent when possible, one after the other.

Static data takes longer to transmit. Transmit rate every 6 minutes, 24B typically sends a minute later than 24A.


Report Rate of AIS 800 Dynamic Data

AIS transponders send position updates based on speed over ground of the boat and transmit updates at different intervals based on the Class A or Class B used. Below is the information based on the AIS 800  

Ship SpeedNominal Reporting IntervalIncreased Reporting Interval
≤ 2 knots, at anchor, or mooredevery three minutesevery three minutes
2 - 14 knotsevery 30 secondsevery 30 seconds
14 - 23 knotsevery 15 secondsevery 30 seconds
> 23 knotsevery 5 secondsevery 15 seconds


Related