What Is Ais; Classes Of Ais - Raymarine AIS250 User Manual

Chapter 1: Important information

What is AIS?

AIS permits the non-verbal exchange of navigation information
between vessels and shore-side vessel traffic centers. AIS uses
digital radio signals to broadcast information about the vessel to
other ships and shore based stations via dedicated VHF
frequencies in the maritime band.
AIS will not replace radar because it is unable to detect land-
masses and navigational beacons, but it can be used as a
significant enhancement to currently available technology.

Classes of AIS

Your AIS250 is a receive-only unit that will receive messages
from vessels carrying Class A or Class B transceivers.
Class A
A Class A transceiver transmits and receives AIS signals. It is
currently compulsory on all commercial vessels that exceed 300
tons that also travel internationally
Information transmitted
The following information can be transmitted by a Class A AIS
system:
• Static data
This includes information such as Ship's name, type, MMSI
number, call sign, IMO number, length and beam and GPS
antenna location.
• Voyage related data
This includes information such as draft, cargo, destination,
ETA and other relevant information.
• Dynamic data
This includes information such as time (UTC), ship's posi-
tion, COG, SOG, heading, rate of turn and navigational sta-
tus.
• Dynamic reports
These are ship's speed and status.
• Messages
These are alarms and safety messages.
You should remember that not all vessels will transmit all of the
information.
Class B - (Recreational vessels not covered by
suitable Class A)
Class B transceiver's are suitable to vessels under 65 feet in
length and is not compulsory.
You should NOT assume that any class of AIS receiver is
displaying all/any smaller vessels within your range.
Note: All messages contain the Ships individual MMSI number for
unique reference identification purposes along with the
data in the following table. Not all the information in the fol-
lowing table is necessarily transmitted by every vessel.
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