Automatic Identification System (AIS) Overview

Vocabulary flashcards covering AIS operational principles, system classes, network technologies, transmitted data categories, frequencies, SOLAS carriage requirements, and display integrations.

Automatic Identification System (AIS)

An automated tracking system that broadcasts a vessel's position, speed, course, and identity via VHF radio waves to improve maritime safety and prevent collisions.

SOTDMA

Self-Organizing Time Division Multiple Access; network technology used by Class A AIS that reserves dedicated time slots to ensure continuous transmission without signal jamming.

CSTDMA

Carrier-Sense Time Division Multiple Access; network technology used by Class B AIS that listens for a gap in traffic before transmitting, potentially causing transmission delays.

Class A AIS

A high-power ($12.5\,\text{Watts}$) AIS transponder required on commercial ships over $300\text{ GT}$ and passenger ships, featuring fast update rates of $2$ to $10\text{ seconds}$ when moving.

Class B AIS

A low-power ($2\,\text{Watts}$) AIS transponder designed for smaller craft like recreational or fishing vessels, transmitting basic static data every $30\text{ seconds}$ to $3\text{ minutes}$.

Class C AIS

A non-transmitting AIS unit that only receives broadcast data from Class A or B systems, enabling a vessel to see surrounding traffic without broadcasting its own position.

Class A vs Class B Systems

Class A uses high power ($12.5\,\text{Watts}$), SOTDMA, and fast update rates ($2\text{--}10\text{ s}$) for commercial vessels, while Class B uses low power ($2\,\text{Watts}$), CSTDMA, and slower update rates ($30\text{ s--}3\text{ min}$) for smaller craft.

AIS 1

Maritime VHF radio channel 87B operating on $161.975\,\text{MHz}$ in simplex mode for ship-to-ship AIS broadcasts.

AIS 2

Maritime VHF radio channel 88B operating on $162.025\,\text{MHz}$ in duplex mode for ship-to-shore AIS broadcasts.

Static Data

Fixed vessel information including IMO number, MMSI, call sign, vessel name, ship type, and dimensions, programmed during installation and broadcast every $6\text{ minutes}$.

Dynamic Data

Real-time vessel movement metrics including GPS position, Course Over Ground (COG), Speed Over Ground (SOG), heading, rate of turn, and navigational status, transmitted automatically based on speed and course changes.

Voyage-Related Data

Route and trip parameters manually entered by the bridge crew (current draught, hazardous cargo type, destination, and ETA) and transmitted every $6\text{ minutes}$.

Safety-Related Messages

Free-format digital text communications sent over AIS to broadcast localized warnings, such as iceberg sightings or floating hazards, to nearby ships or shore stations.

SOLAS Chapter V, Regulation 19.2.4

International IMO regulation requiring AIS carriage on all passenger ships, all international voyage ships of $300\text{ GT}$ and above, and domestic cargo ships of $500\text{ GT}$ and above.

Vessel Traffic Services (VTS)

Shore-based marine traffic monitoring systems that utilize AIS signal reception to track vessels, manage coastal traffic, and enhance port security.

CPA and TCPA

Closest Point of Approach and Time to Closest Point of Approach; key safety calculations computed by AIS-integrated navigation systems to trigger collision risk warnings.