AIS Explained

What is AIS and how can it keep boaters safe?

So, we have all heard the acronym AIS bantered around at some point. It may have been a feature of your new chartplotter or something mentioned on a YouTube video you watched. But what is it exactly, and why should you care?

What does AIS do?

AIS, or Automatic Identification System, is a navigation safety communication system designed to help marine traffic travel safely in busy areas by augmenting situational awareness. Combined with radar and an alert boater/mariner, it can help track vessels nearby and communicate more quickly and accurately with them, all helping to avoid collisions.

Designed to show on either a dedicated display or a chartplotter, nearby vessels transmit AIS signals with their position and other relevant information. When the screen’s cursor hovers over the image of the vessel transmitting its signals, data is displayed with information about that vessel.

AIS utilizes VHF transmissions through a dedicated transceiver to broadcast two different AIS messages. The first is a position report comprising the vessel’s location, position accuracy, course, speed and status. The second message includes data specific to the vessel, such as its name, dimensions, vessel type, destination and ETA. The transceivers broadcast and receive this information from VHF frequency transmissions within the transceiver’s range. There is also terrestrial-based AIS (T-AIS) used by port and maritime authorities, privately owned systems and satellite-based AIS (S-AIS). These satellite systems remove the limitation of the range found with other systems. You can even locate and track vessels all over the world with websites that utilize land- and satellite-based AIS transmissions, such as MARINEFINDER.COM, VESSELFINDER.COM and MARINETRAFFIC.COM.

AIS was first devised as a requirement for all commercial vessels over 300 gross tons and all passenger ships by the International Maritime Organization’s International Convention for the Safety of Life at Sea. The AIS equipment found on these vessels is known as Class A.

In 2014, the U.S. Coast Guard implemented legislation that requires most commercial vessels of any size operating in U.S. waters to install and use a certified AIS transceiver. This legislation led to the popularity of Class B AIS, which is not only available for smaller commercial vessels but also recreational vessels that wish to broadcast their AIS information. These vessels now have a more economical way of doing so with the lower-cost Class B units.

Class B AIS units are available as standalone systems, such as those offered by Vesper and Icom, and many marine electronics manufacturers have their own units. These are designed to interface with their line of multifunction displays and can be displayed on chart and radar screens with features simplifying AIS target interpretation. Many comprise a black box or module that connects to the display and a splitter or dedicated VHF antenna for transmitting and receiving AIS signals.

There is also a third class of AIS that is the most common. It’s a receive-only AIS and can be found on many modern VHF radios. These units do not transmit any information but display AIS information and allow Digital Selective Calling (DSC) to an identified AIS vessel. Many receivers can display AIS targets nearby on their own screen or can transmit them via NMEA to a chartplotter, overlaying the information on the chart. This is a very economical way to have greater situational awareness, particularly in areas of heavy marine traffic. The downside to this class of AIS is that others are not necessarily aware of your vessel through AIS because you are not transmitting any information.

Having AIS aboard also helps in emergency situations with devices like ACR’s AISLINK MOB beacon. This device has integrated DSC and GPS. Should a crew member fall overboard, the AISLINK sends an alert message to all local vessels identifying the person in distress, and their location is shown as an AIS target on their screen. ACR recently introduced a PLB, the ResQLink AIS PLB, that also has an AIS transmitter, so the person overboard has both a satellite beacon and an AIS beacon in one small device.

No matter which form of AIS is being used, it’s a fact that they help any skipper with situational awareness and play a valuable role in safety at sea. ★