| What does AIS stand for? |
| AIS stands for Automatic Identification System. |
| What is AIS used for? |
| AIS is used for the identification of ships at sea. The ships transmit data to each other to describe their current positions and intended course. This is especially important when visibility is restricted, at night for example. |
| What information is broadcast and how often? |
| When a vessel is moving this information is broadcast every 2 to 10 seconds depending on the speed of the vessel. This extends to every 3 minutes when the vessel is anchored. The unique identification or MMSI number of the vessel and navigation status (for example at anchor, under way, not under command). Course, heading, position, rate of turn, speed and the time this information was generated is also broadcast. Other data broadcast every 6 minutes is the IMO number, radio call sign, name, type of vessel, dimensions, draught, destination and ETA, global positioning system and the position of the GPS system on the vessel. |
| Which vessels are required to show this data? |
| All passenger ships (except domestically working passenger ships less than 300 gross tonnes), internationally and EU travelling ships of 300 gross tonnes or more (500 gross tonnes for domestically working cargo ships). |
| How is this information broadcast? |
| This information is broadcast automatically broadcast using a built in VHF radio. |
| What frequencies is AIS broadcast over? |
| There are two frequencies over which this information is broadcast. Class A vessels broadcast over 161.975MHz and class B vessels broadcast over 162.025MHz. |
| What are class A and class B vessels? |
| Class A vessels are primarily commercial vessels. Class B vessels tend to be smaller or used for recreational purposes. The main difference is the amount of information transmitted. Class B messages do not provide as much information and are broadcast much less frequently than class A. |
| What equipment is required to receive these messages? |
| The discriminator output of a VHF radio or the serial output from a dedicated AIS receiver, connected to a PC running AIS plotting software such as Shipplotter. |