Article by Capt. Steve Katz
AIS
Automatic Identification System, or more commonly referred to as AIS, is an electronic vessel tracking safety and collision avoidance system used by other vessels and land stations. The AIS system electronically exchanges information about each transmitting vessel with other vessels in the nearby area – about a 20 mile range.
With the proper hardware, AIS signals are automatically broadcast digitally on a frequency of 161.975 MHz and 162.025 MHz from the vessels AIS transmitter to all nearby AIS receivers. While AIS systems are mandatory for most commercial vessels, many recreational vessels have chosen to add this hardware as a safety feature.
There is a technical and cost difference in the ability to receive AIS signals compared to the ability to broadcast AIS signals. Many recreational boaters have the ability to receive AIS signals but do not broadcast. This allows them to “see” other vessels; like using radar, AIS can see around the corner and can also “see” in rain and fog. As a recreational boater, knowing where other vessels are is a helpful collision avoidance and safety feature. Reading the other vessels AIS data, you are able to see the other vessels name, radio call sign, MMSI number, location, speed, heading and possibly more information. A useful feature is that if you have the vessels MMSI number, you can make a DSC (Digital Selective Calling) direct call to their marine VHF radio. These features are great in a situation where you need to contact another ships captain and let them know where you are or ask what their intentions are. Using an AIS receiver is a little like spying. You can see and read about the boats around you, but they do not know you are listening.
AIS receivers are available at a reasonable cost and are available as a built-in feature on some VHF radios and also as a standalone hardware device. These stand-alone devices need to be connected to your chart plotter using NMEA 0183 or NMEA 2000 to transfer the received data. Stand-alone AIS receivers, relying on an existing chart plotter and sharing your VHF antenna, start around $250. VHF radios with built in AIS receiver and graphical display start around $400.
If you really want to be “seen” in the AIS environment, you will need to install an AIS transceiver that can transmit your vessels data. A transceiver is both a transmitter and receiver in one unit. The hardware costs begin around $700 for a Class B transceiver. An AIS transceiver is required to have its own GPS antenna and should have its own AIS/VHF antenna for broadcasting and receiving. The processor box is programmed by a technician with the ships static data, such as vessel name, radio call sign, MMSI number, vessel type, vessel dimensions, GPS antenna location, etc. Don’t worry that in a tournament everyone will know where you are fishing. Most AIS transceivers have an optional feature that lets you disable the transmitting function, by enabling a “silent” mode.
AIS transceivers are available in two classes: Class A and Class B.
Class A transceivers report their position autonomously every 2 to 10 seconds dependent on the vessel’s speed and/or course changes (every three minutes or less when at anchor or moored). It transmits the vessel’s static and voyage related information every 6 minutes. Class A systems are also capable of text messaging safety related information and AIS Application Specific Messages, such as meteorological and hydrological data, electronic Broadcast Notice to Mariners, and other marine safety information. Class A transceivers are usually found on large, regulated vessels and have a much higher cost than Class B AIS hardware designed for unregulated vessels recreational use.
Class B AIS transceivers operate with less transmitting power and transmit the vessels data report less often. As with Class A transceivers, they report the vessel’s static data every 6 minutes, but not any voyage related information. Class B AIS broadcasts can be de-prioritized by a Class A device if there is heavy traffic on the AIS broadcast frequencies, such as in a busy port or shipping lane. Even if you only receive AIS, Class A versus Class B can make a big difference on how far away you receive data, the specific data your system receives and how often you receive it.
Now that we know a little on how it works, how can this AIS data be used while we are out on the water? When properly connected, most chart plotters will show you a triangle on the display screen representing the AIS vessel, along with more detailed information when you select that vessel. This information will help you or your system determine if there is a possibility of collision with the AIS vessel and allow you to make speed or heading changes based on the AIS data.
One of the best features of installing a Class A or Class B transponder is that your vessel shows up on the other vessels navigation systems. This allows another vessel to know where you are and therefore, if needed, allows one of you to alter course to maintain safe separation distance of the vessels.
One example where local anglers could benefit from an AIS transmitter is when you are fishing an overnighter in the Canyon and a large freighter seems to have plotted its course directly through the fishing fleet. Instead of wondering if the other Captain sees you in the dark and you are unsuccessful trying to make radio contact, your AIS transceiver allows you to be confident that the other boat captain can see your ships positioning on their electronic navigation system. Commercial Captains are usually required to make contact with other vessels to determine if they are going to alter course or stand-on.
An AIS system is a great, simple addition to your existing navigation equipment and an important navigation tool for collision avoidance.
Captain Steve Katz is the owner of Steve’s Marine Service and holds NMEA, AMEI and NMEA2000 certificates along with ABYC Master Technician certification and factory training from many manufacturers. To reach Steve, call (631) 264-1600.