AIS and MMSI information MMSI

MMSI stands for Maritime Mobile Service Identity. This is a unique 9-digit number assigned to boats with certain kinds of radio equipment. You can think of it as a Social Security number for your boat. Search and rescue authorities including the Coast Guard use the MMSI to learn background information about a vessel in distress (e.g., owner’s name, intended route, and other radio equipment on board). An accurate MMSI database helps to protect lives and property by reducing the time needed to locate vessels in distress. The MMSI number also has non-emergency functions. When properly set up in your Marine VHF radio, it allows you to see the name of who is calling (like caller ID), set a notification so you can see if you missed a call, or alert a buddy that you want to speak with them without having to listen to every unrelated call on Channel 16.
Click here for instructions on how to get a MMSI number

Maritronics AIS for Dummies

Here Linda is pointing at the "Marine Traffic" app on my phone. Another app is "FindShip."

AIS from least expensive to most expensive: pros and cons

Free apps like "Marine Traffic" and "FindShip" can be loaded on your smartphone. Not technically AIS, they are a "poor man's" way to know where AIS-equiped vessels are (assuming your phone has signal and there is a nearby volunteer participant loading data to the internet in the vicinity of your boat). Pros: Using these apps, you can see where millions of vessels are all around the world. You can keep track of ''favorite vessels" and search for the location of a vessel by name (the vessel must have a AIS transceiver. See examples of that equipment further down on this list). Cons: This method has many "blind spots" where nothing is shown even though an AIS-equiped vessel mey actualy be there. This is not a definitive way to test an AIS transceiver.

"Receive-Only" AIS

"Receive-Only" AIS allows you to see all AIS-equipped vessels within about 10 miles regardless of internet connection. It can work as a stand-alone unit but is usually incorporated into a VHF marine radio. It connects to your chartplotter with a NMEA connection.
  • Reliably works all the time within about 10 miles.
  • Less expensive than a 2-way AIS tranceiver.
  • Other vessels do not see the name and position of your boat.
  • You won't show up on internet-based apps.
  • Less expensive than a 2-way AIS transceiver, but you probably still should in order to enable the distress feature of your VHF Marine radio.
Background photo: This screenshot shows a green arrowhead icon, which represents a boat with an AIS transceiver resting at its slip in the Sunnyside Marina in Stillwater. This is what your Chartplotter will look like if you are within range (about 7 to 16 miles). It shows the name of the boat, its MMSI number, distance and bearing, and other information. Our thanks to customer Jeff Lampe and his vessel Diamond Cutter for allowing us to use this image.
Raymarine's AIS350 Receive-Only AIS module

Two-way send and receive AIS transceivers: other vessels see you!

Garmin's AIS800 transceiver module.

Class B AIS transceiver

This type of AIS is gaining popularity with many pleasure boaters. When you order a Class B AIS transceiver from our company, Maritronics programs your boat's name and MMSI number into this module. It is mounted out of sight and connected to your multifunction dispay (chartplotter) with NMEA connection. Two antennas are also installed. With a Class B AIS transceiver, you see other AIS-equipped vessels. AND THEY ALSO SEE YOU! This can be very helpful when traveling the Mississippi or other areas where you encounter many towboats (barges). A class B AIS eliminates guesswork about the position and names of these vessels. It even calculates when you will meet. They can then radio you with the best way to pass.

You must obtain a MMSI number.

Class A AIS Transceiver: the most powerful AIS

  • Usually on a mega yacht or commercial vessel.
  • Can transmit name and position farther at a slightly more powerful rate.
  • Can work better in very busy ports with hundreds of AIS vessels present.
  • The most expensive AIS.
  • Commercial and excursion vessels must have Class A AIS.
  • You can view information on a small screen, but usually you view AIS on your Multifunction display (Chartplotter) connected with NMEA.
  • You must obtain a MMSI number.


Furuno's FA-170 Class A AIS Transceiver.