Marine AIS Systems for both leisure and commercial vessels, the primary method of collision avoidance for marine traffic.
In simplistic terms -
AIS transceivers = 'see and be seen'
AIS receivers = 'see'
AIS Identifiers = 'be seen'
The difference between Class A AIS and Class B AIS is explained in more detail below:
Q = What is the range for AIS receivers?
A = Since AIS uses the same VHF frequencies as marine VHF, it has similar radio reception capabilities which is basically line of sight. This means that the higher your VHF antenna is
mounted, the greater the reception area will be.
Reception from Class A vessels that are 20 or even 30 miles away on open water is not uncommon.
Class B transponders use lower power for transmissions, therefore you can expect Class B vessels to be acquired when they are 5 to 7 miles away.
Note that AIS has a major advantage over radar since it can see ships within radio reception range that are behind large objects, such as other ships or points of land.
Q = Is it possible to connect my AIS receiver or transponder to a chart plotter?
A = Today most modern chart plotters support the connection of an AIS receiver or transponder and are able to display AIS targets. Some of the manufacturers that support AIS include
Raymarine, Garmin, Standard Horizon and Furuno. For further information contact your supplier and ask about AIS support in their product. For more information on how to use the AIS receivers
or Class B transponder that we sell with an AIS-capable chart plotter
Q = Can I use an existing marine VHF antenna with an AIS receiver or transponder?
A = Yes, you can use a splitter to share your existing VHF antenna to your VHF/DSC radio and your AIS receiver. You must use an active splitter that automatically disconnects the signal to
the AIS device if a transmission is detected from the VHF radio.
Q = What kind of information is broadcast for each vessel and how often is it updated?
A= Class A AIS transponder broadcasts the following information every 2 to 10 seconds while underway, and every 3 minutes while at anchor:
MMSI number - unique referenceable identification
Navigation status - at anchor, under way using engine or not under command
Rate of turn - right or left, 0 to 720 degrees per minute
Speed over ground - 1/10 knot resolution from 0 to 102 knots.
Position accuracy - differential GPS or other and an indication if RAIM processing is being used
Longitude - to 1/10000 minute and Latitude - to 1/10000 minute
Course over ground - relative to true north to 1/10th degree
True Heading - 0 to 359 degrees derived from gyro input
Time stamp - The universal time to nearest second that this information was generated
In addition, the Class A AIS unit broadcasts the following information every 6 minutes:
MMSI number - same unique identification used above, links the data above to described vessel
IMO number - unique referenceable identification (related to ships construction)
Radio call sign - international call sign assigned to vessel, often used on voice radio
Vessel name - name of ship, 20 characters are provided
Type of ship/cargo - there is a table of possibilities that are available
Dimensions of ship - to nearest meter
Location on ship where reference point for position reports is located
Type of position fixing device - various options from differential GPS to undefined
Draught of ship - 1/10 meter to 25.5 meters (note air-draught is not provided)
Destination - 20 characters are provided
Estimated time of Arrival at destination - month, day, hour, and minute in UTC
Class B AIS transponders also provide static vessel information every six minutes however the information only includes:
Radio call sign
Length and beam of vessel
Type of vessel
Position updates for Class B transponders are broadcast less often than Class A transponders. Vessels going less than 2 knots transmit position updates every 3 minutes while vessels traveling
more than 2 knots transmit position information every 30 seconds.
For this reason it is recommended that you consider purchasing a true dual channel AIS receiver if you plan to use the AIS receiver in an area where Class B transponders are in use.