FAQ

An AIS relies on the marine Very High Frequency (VHF) radio communication bandwidth, specifically Channel 87 – 161.975 MHz and Channel 88 – 162.025 MHz. Using radio waves, AIS works by Line Of Sight (LOS), but due to the radio wavelengths utilised it is possible to receive AIS transmissions that have reached around buildings, vessels, and geographical features such as coastal headland.

An AIS works by sending and receiving ‘packets’ of information using a VHF transponder. Information is gathered from the on board sensors and from previously entered information about the vessel. This information is transmitted ship-to-ship, and also ship-to-shore either received by an AIS shore station or by certain AIS-enabled satellites.

Class A and Class B ‘packets’ or transmissions are scheduled within ‘slots’, with precedence given to fast moving / close proximity vessels if in high traffic areas. Both Class A and Class B transmissions are visible to each other.

To enable all vessels to share this data environment effectively, Class A transponders use a defined method known as Self Organising Time Division Multiple Access (SOTDMA). Class B transponders use a separate defined method known as Carrier Sense Time Division Multiple Access (CSTDMA).

The letters AIS stand for Automatic Identification System.

AIS enables the free exchange of static and dynamic vessel related information on a point to multi-point basis, i.e. Ship to Ship, Ship to Shore – this is known as “4S”.

Via VHF radio signals, packets of data are regularly transmitted and received by any vessel equipped with an AIS transponder (transponder a.k.a. transceiver = transmits and receives data). Depending on the class of vessel, this data can include the following:

Dynamic data, such as vessel movements, are sent every few seconds. Static data, such as vessel identification and dimensions, are sent every few minutes

 

An important difference between Class A and Class B AIS transponders is that Class A units will always transmit their packet of information under all circumstances, but Class B will first make sure that there is a free slot available before it transmits its packet of information.

This is not an issue in most maritime areas of the world because of the following:

A good example of a congested waterway is the Bosporus in Turkey. In this maritime environment (probably the most crowded in the world with 450 vessels operating within in a distance of 30NM), on average 200 Class A and 250 Class B vessels easily co-exist without reducing the safety of any maritime user. In addition to Class A, many Class B reports are successfully received by the AIS shore station that monitors this area.

The use of AIS is mandated for certain types of vessel, whereas in other cases carriage is voluntary, for example:

Including the USA, a growing number of countries in addition to the EU, India, China, Russia and others, are preparing to mandate the use of either Class A, or both Class A and Class B transponders, on all, or certain types of vessels used for specific purposes.

These national initiatives have been based on documented improvements in increased Maritime Domain Awareness (MDA) by means of AIS, namely Safety, Security, Economic and Environmental management.

• Individual vessel users can be confident that, once an appropriate distress call has been issued, their current real-time position can be recalled by local AIS equipped assets, such as Naval, SAR (including airborne), and coastal authorities. AIS is being used to combat piracy in several national and international waters.
• Organisations (private, governmental and non-governmental), can benefit from monitoring their marine assets in real time, ensuring the safest possible day to day operations for their vessels and crew. AIS is being used to combat piracy in many national and international waters. AIS equipped vessels deviating from a defined course can be monitored by coastal or Satellite AIS (S-AIS), and automated alerts created for fleet managers to act accordingly.
• National authorities can benefit from an increased Maritime Domain Awareness (MDA), ensuring that they can monitor all AIS equipped vessel activities in their littoral waters and beyond. AIS is being used to combat piracy, human trafficking, the transport of narcotics and other illegal cargo.

• Individual vessel users can be confident that, once an appropriate distress call has been issued, their current real-time position can be recalled by local AIS equipped assets, such as Naval, SAR (including airborne), and coastal authorities. AIS is being used to combat piracy in several national and international waters
• Organisations (private, governmental and non-governmental), can benefit from monitoring their marine assets in real-time, ensuring the safest possible day to day operations for their vessels and crew. AIS is being used to combat piracy in many national and international waters. AIS equipped vessels deviating from a defined course can be monitored by coastal or Satellite AIS (S-AIS), and automated alerts created for fleet managers to act accordingly.
• National authorities can benefit from an increased Maritime Domain Awareness (MDA), ensuring that they can monitor all AIS equipped vessel activities in their littoral waters and beyond. AIS is being used to combat piracy, human trafficking, the transport of narcotics and other illegal cargo.

• Individual vessel users benefit greatly, as the installation of an AIS is a small investment leading to a large return in safety features. AIS is a compliment to, not a replacement for radar and good watch-keeping, but in terms of insurance, AIS can provide a legally acceptable historical record of vessel positions, should an incident unfortunately take place.
• Organisations (private, governmental and non-governmental), concerned with balancing operational expenditure can benefit from monitoring their marine assets in real-time, ensuring the most efficient vessel movements between berths, travelling to and from sites (i.e. wind farms), and monitoring vessel acceleration and speed for fuel consumption.
• National authorities can monitor and manage vessels that intend to enter port well in advance of their arrival, they can manage those that are loading / unloading cargo, and see that berths vacated on time by departing vessels. In addition, all port work vessels, including those used for pilotage can be managed by means the same AIS technology.

• Individual vessel users, including fishers (leisure, subsistence and commercial) can be confident that they are not inappropriately accessing zones of prohibited or limited activities, such as Marine Protected Areas (MPAs). These zones are often monitored by shore-based radar and AIS systems, the GPS boundaries of which can be transmitted to vessels equipped with AIS and a suitable chart display. A number of these zones also define speed restrictions, and limit the number of vessels that can access the area at one time (i.e. Eco-tourism). Carriage of an AIS unit, monitored from shore by the relevant authorities, allows the vessel operator to prove their compliance with these local restrictions, and avoid punitive action.
• Organisations (private, governmental and non-governmental),concerned with operating work vessels (i.e. wind farm, aquaculture), or fishing vessels (subsistence and commercial) can benefit from monitoring their marine assets in real time. They can prove their compliance with restrictions imposed on vessel operations nearby, within, transiting and leaving zones of prohibited or limited activities, such as Marine Protect Areas (MPAs) and No Take Zones. A number of these zones also define speed restrictions and limit the number of vessels that can access the area at one time. Carriage of an AIS unit, monitored from shore by the relevant authorities, allows the vessel operator to prove their compliance with these local restrictions, and avoid environmental damage and punitive action.
• National authorities can ensure that vessels carrying cargo defined to be hazardous to the environment can be safely managed and monitored as they pass through sensitive littoral or international waters such as fishing grounds, within range of restricted zones such as Marine Protected Areas (MPAs), or inside ports of national oversight and responsibility. Work vessels, such as those used for oil spill monitoring and recovery, can be managed and monitored by using AIS, to ensure that a rapid response and effective coordination is maintained at all times. AIS systems, both vessel and shore-based, enable a national authority to comply with the strict international laws and guidelines that relate to reducing or eliminating the risks associated with the discharge of (accidental or deliberate) vessel borne environmental pollutants.

The equipment required to benefit from an AIS depends on both the installation and the users. In most cases, there are two common AIS installations, and three types of user:

Individual users require at least the following equipment:

A suitable Electronic Chart System or Multi-Functional Display to display the AIS data collected within range (with acceptable AIS data input feeds such as NMEA 0183 / 2000) with suitable data cable fed from the AIS transponder

Individual users require at least the following equipment:

Organisations (private, governmental and non-governmental) require at least the following equipment:

Organisations (private, governmental and non-governmental) require at least the following equipment:

National authorities require at least the following equipment:

National authorities require at least the following equipment: