AIS (Automatic Identification System) is a transponder system as it has been known from aviation for a long time. Since December 2000, it has been chosen by the IMO as a mandatory standard and provides accurate data on the status of an AIS-equipped vessel to all other vessels in the vicinity.
In principle, AIS equipment can be distinguished between Class A and Class B transponders (transmitters and receivers) and receivers only:
With a pure receiver, only the other boats in the vicinity are seen. Here there are various devices on the market with different data interfaces. For the devices with NMEA0183 interfaces, the baud rate is fixed at 38400 baud for the AIS data sets. So if you have an older chart plotter that cannot handle this baud rate, you can connect the AIS receiver but you will not get AIS data. If the AIS receiver (e.g. Raymarine AIS350) sends NMEA2000 or SeaTalkNG data and your chartplotter also has this interface, there is no problem. There are also AIS receivers with USB interface (e.g. McMurdo M15), which can then be connected directly to a PC e.g. with the AIS-Viewer software.
Please also note that an AIS receiver either needs its own VHF antenna or an antenna splitter must be used if the existing VHF antenna is used for both VHF radio and AIS.
With a transponder, one’s own ship’s position is always transmitted with additional data, ensuring that one’s own ship is seen by other boats – which are equipped with AIS. For this purpose, each AIS transponder requires its own GPS antenna.
This is prescribed by the IMO and the antenna is e.g. with the Raymarine AIS700 in the scope of supply. Also an AIS transponder needs its own radio antenna (VHF broadband antenna with 20 MHz) or an internal antenna switch (e.g. already installed in the Raymarine AIS700).
In addition to the AIS data of ships with transponders, the virtual sea marks (AtoN = Aids to Navigation) are also received. In many cruising areas, sea marks and buoys are already replaced by AtoN. Thus, these sea marks are physically no longer present at all and are only displayed on devices with an AIS receiver connected.
AIS transponder classes
There are also several points of difference between Class A, Class B and Class B+ transponders (these are receivers with SOTDMA technology – as with Class A):
On a modern multifunction display (e.g. Raymarine Axiom series) the AIS data from the receiver or transponder can be displayed directly in the chart image and/or also in the radar image. The most important data can be displayed as a “window”, details can be called up. Of course, a display with all AIS data in a table is also possible.
An AIS display window is also available on intelligent on-board instruments (in the example a Raymarine i70S instrument). Note, however, that AIS displays are only possible if also (but today actually self-evident) a GPS-Im system is.
Mobile AIS receiver or transponder
Especially for charter drivers or transfer skippers, there are also mobile AIS receivers or transponders – which work, for example, with a tablet as a display. With these mobile devices (e.g. DigitalYacht NOMAD), a VHF antenna with suction cup (included) is simply mounted and the transponder delivers the AIS data via USB to a PC or via WiFi to a tablet. The required GPS is built into the transponder’s housing. Note, however, that the MMSI number (this is required for each transponder) can only be entered once. Since this number is always fixed for a vessel, mobile transponders are of very limited use. Without an MMSI number, these devices operate as pure receivers.
In conclusion, it can be said that AIS is an extremely effective system that significantly increases safety at sea. In Thailand, AIS is even mandatory and without an AIS transponder, entry by ship is not allowed.
Information and advice
Specialist for consulting and installation of yacht electronics is the company WERNER OBER GmbH & Co KG – Yachtelektronik.
Werner Ober GmbH & Co KG
6890 Lustenau | Austria