Ais Overview; Classes Of Ais - Raymarine AIS 350 Installation Instructions Manual

2.5 AIS overview

Your AIS device uses digital radio signals to exchange 'real-time'
information between vessels, shore based stations, or aids to
navigation (AToNs) on dedicated VHF frequencies. This information
is used to identify and track vessels in the surrounding area and to
provide fast, automatic and accurate collision avoidance data.
Although AIS augments your radar application by operating in radar
blind spots and detecting smaller AIS-fitted vessels, it does not
replace radar, as it relies on receiving transmitted AIS information
and therefore cannot detect objects such as landmasses and
navigational beacons.
NEVER assume that AIS is displaying information from all vessels
in the area, because:
• Not all vessels are fitted with AIS
• Although it is mandatory for larger commercial vessels to carry
AIS, it is not mandatory to use it.
AIS should be used only to augment radar information, not substitute
it.
Warning: AIS limitation
Never assume that your AIS is detecting all vessels
in the area. Always exercise due prudence and do
not use AIS as a substitute for sound navigational
judgement.
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2.6 Classes of AIS

The AIS350 is a receiver that receives messages from vessels,
land base stations, or aids to navigation (AToNs) carrying Class A
or Class B transceivers.
The AIS650 is a Class B transceiver that receives messages from
and transmits messages to vessels, land base stations, or aids to
navigation (AToNs) carrying Class A or Class B transceivers.
Class A transceivers
Class A AIS transceivers transmit and receive AIS signals. AIS
transceivers are currently mandatory on all commercial vessels
exceeding 300 tons that travel internationally (SOLAS vessels).
The following information can be transmitted by a Class A AIS
system:
• Static data. Includes information such as vessel name, vessel
type, MMSI number, call sign, IMO number, length, beam and
GPS antenna location.
• Voyage related data. Includes information such as draft, cargo,
destination, ETA and other relevant information.
• Dynamic data. Includes information such as time (UTC), ship's
position, COG, SOG, heading, rate of turn and navigational status.
• Dynamic reports. Ship's speed and status.
• Messages. Alarms and safety messages.
Remember that not all vessels will transmit all of the information.
Class B transceivers
Class B AIS transceivers transmit and receive AIS signals, but use
a reduced set of data compared to Class A (see Data Summary). A
Class B AIS transceiver can be fitted on any vessel not fitted with a
Class A transceiver, but is not mandatory aboard any vessel.
AIS350 / AIS650