To first understand whether you need AIS you have to know what it is does, and how you can benefit from it. 
What is AIS? AIS stands for Automatic Identification System. It is a system that automatically tracks other boats and ships that are transmitting AIS for collision avoidance.  Information transmitted via AIS is data about the vessel itself, such as the MMSI number, its name, size, type, cargo, and draft. It also includes data about the ship’s movements, including speed, destination, ETA, and COG. This info is available to anyone who has an AIS receiver.  AIS comes in two forms Class A and Class B.  Class A AIS has a higher transmit power, and transmissions are sent frequently, every few seconds, and given priority over information from Class B transceivers.  Class A AIS transceivers have a large built in Display, and multilingual capability. These systems are mandated for large commercial cargo and passenger ships, and more recently smaller work boats and commercial fishing boats.  Class B AIS units are less powerful (2 watts), don’t have to have a display screen and don’t have to both send and receive AIS information.   There are Class B AIS that are just receivers, and only display the information on vessels in your area but do not transmit your information.

Next let’s look at which one meets your needs.  If you are a commercial vessel probably a Class A is best for you, if you are a large pleasure craft whether power or sail once again Class A might be best but possibly a Class B transceiver may be all you need.  (It is best to consult Coast Guard Requirements if you are unsure) Lastly if you have a smaller sport fishing boat or sail boat a Class B receiver would be a benefit to add another tool for collision avoidance.  In tight waterways like rivers and the Intracoastal Waterway your AIS may show a barge that requires you to pass on the “wrong” side because they cannot change their path or the water is too shallow for them on that side.  Many receivers have collision alarm settings, or warn you of ships that are travelling in a direction and speed such that they have the potential to become a collision problem.  The crowded harbors, that are our favorite boating areas, can present challenges with clutter on even the largest navigation screens, so you may want to look for an AIS that offers the ability to clear vessels from the screen that do not present a collision threat.

Click Here to View AIS Transceivers - Send And Receive 

Click Here to View AIS Receivers - Receive Only 

Now let’s look at how they work.  Believe it or not it is through VHF radio frequencies 161.975 MHz and 162.025 MHz, and the information they send and receive is based on the ship itself like its MMSI #, name, size, type, cargo, and draft; as well as the ship’s moving data like speed, destination, course, and ETA.  If you don’t know where to get a boat ID like your MMSI # it can be obtained through approved organizations such as BOAT US 1-800-563-1536, SEA TOW 1-800-4SEATOW, U.S. Power Squadron, and Shine Micro(primarily for AIS). Most of these organizations provide MMSIs at no charge even to nonmembers.  Even if you are not using AIS you should have an MMSI # to be used with DSC on your VHF radio.