AIS: The 101 Guide to Everything You Need to Know

AIS is mandatory for all commercial vessels over 300 tons and all passenger ferries recognized under the SOLAS convention. Its use has also has become a staple on board many leisure boats around the world. So, what does it do? and why is it so? important?

What is AIS?
AIS stands for Automatic Identification System. This tracking system uses AIS transmitters on board ships; ships, and the information from AIS is used in many scenarios, from pleasure boats and inspection vessels to commercial vessels and coast guards. The list of AIS users is endless, thanks to how usable and accurate the information is.

Simply put, AIS is an avoidance system collisions. Any vessel equipped with AIS (either Class A or Class B) will automatically transmit its identity, position, course and speed in combination with other information. This information is used by both other boats and shore stations. Shore stations that have access to this information mean that safety operations can manage traffic, helping to control and reduce the number of hazards and collisions between boats navigating on; the water.

"Each AIS system consists of a VHF transmitter, two VHF TDMA receivers, a VHF DSC receiver and standard marine electronic communication links (IEC 61162/NMEA 0183) to the ship's display and sensor system (AIS Schematic). Position and time information is normally derived from an integrated or external global navigation satellite system (eg GPS) receiver, including an intermediate frequency differential GNSS receiver for accurate coastal position - and inland waters. Other information transmitted by AIS, if available, is obtained electronically from the ship's equipment through standardized marine data connections. Heading information and course and speed over land would normally be provided by all AIS equipped Other information such as yaw rate, pitch and roll, and destination and ETA can also be provided."

Marine Band VHF and AIS work onå a frequency of 156-162MHz. However, AIS works on två frequencies onå a fixed time frame protocol ie: AIS 1 = 161.975 MHz / AIS 2 = 162.025 MHz

4500 time slots are available on; this protocol every minute (2250 on each channel), and the AIS transponders/receivers are referenced to this via the GNSS (GPS) receiver. Class A has higher priority and has "reserved" seats within this time frame, while Class B cannot. This allows Class A communications to have priority, while Class B will only be transmitted if there are free slots. The reason for this is that while both A and B use TDMA, they use different versions. Class A uses SOTDMA (Self Organizing Time Division Multiple Access), while Class B uses CSTDMA (Carrier Sense Time Division Multiple Access). Some newer Class B AIS systems can now work with SOTDMA and newer/more complex Class A receivers will now display Class B vessels.

This information received is divided into three main categories:

• Static data: Name, IMO number, size, call sign etc...
• Dynamic data: UTC, COG/SOG, ROT, Course, Position (Lat/Lon via GPS) etc...
• Voyage data: Type of cargo på ship, destination, ETA etc...

AIS transponders and land stations collect this information to form a screen that RADAR på an MFD. Quite often, AIS is used in combination with radar to provide an improved graphical display of; MFD, giving the helmsman or boatman a more complete picture of what is happening around them.

Figure 1 – NMEA Transaction Document

What are Class A and Class B AIS?
From 2002 it was made mandatory to have AIS on; all commercial vessels over 300T, and all passenger ferries recognized under the SOLAS Convention. These vessels must have a Class A AIS system. Class A works on a much higher effect for conversion on up to 12.5W, which means that they can send and receive data over a much greater distance than the equivalent in class B. Class B works up to 2W, which means that the transceiver's rä ck width is much shorter, but this is for good reason.

Since class B is recommended for recreational boats and small boats, they usually do not need attention on ship further away på due to their size and manoeuvrability. For example, a 300 meter long tanker carrying hundreds of tons needs a much earlier warning of possible collisions to make necessary course adjustments.

External Because of this, Class A systems must transfer their information much more frequently. Here's the feature:

Class A

• 2 to 10 second Tx interval at pågå only more than 3 knots
• 3 minute Tx interval at anchor or below 3 knots
• Supplementary data is transferred at 6 minute intervals.

Class B

• 30 second Tx interval when going more than 2 knots
• 3 minutes Tx range at anchor or below 2 knots
• Much fewer parameters and supplementary data required

Some things remain the same between class A and B, for example the reference location method på ship, they are both taken with these measurements:




Figure 2 – NMEA Training Document

Another significant difference between Class A and B is the pilot port requirement for; class A system. A Pilot-Port is a data interface on; or with the transmitter/receiver, which provides helmsmen and captains with the necessary traffic and navigation data for the waters around their vessel, usually located on; the normal watch station.

How do our products relate to this?
A common scenario is VHF/AIS which is NMEA 0183, while the chartplotters and MFDs are NMEA 2000. The simple solution for this is our award-winning NGW-1 NMEA bidirectional conversion gateway. The NGW-1 can take NMEA 0183 sentences output from your AIS and convert them to relevant NMEA 2000 PGNs, which are then shared with all devices in your NMEA 2000 network, enabling AIS measurement ;l and öoverlay information onå screen.

We understand that AIS and baud rates can be a bit complicated for those unfamiliar with Marine Electronics, especially; we offer a pre-configured NGW-1 with AIS firmware. This means that the device is already set to NMEA 0183 High-Speed ​​38400 baud rate, with all necessary AIS conversions enabled. It is also possible to configure your "Standard" NGW-1-ISO soå that it behaves onå the same way. By using the latest 2.660 firmware in combination with the Actisense Toolkit, we have made this a simple process. ship, and our W2K-1 try to get the gateway set up to help you reach your goals. Our gateway is connected to your NMEA 2000 network so that it can receive any NMEA 2000 PGN. The W2K-1 can be connected to a tablet/mobile phone, where apps such as Navionics can be used. På because most mobile applications use NMEA 0183 as their data format, W2K-1 has the same conversion engine as NGW-1, which allows W2K-1 to output NMEA 0183 sentences.

In addition to thread connection becoming more popular, such as become on-board computers with map and navigation applications such as Time Zero. If you would like to get your NMEA 2000 data to the PC application, så är ourår NGT-1 NMEA 2000 PC Gateway a fantastic solution right away. The NGT-1 can receive all available PGNs at present, which means that no data will be sent; flowed between your NMEA 2000 network and the computer. Since this unit alsoå äis bidirectional, the PC application can alsoå used to transfer PGNs to the network via NGT-1.