Article by Capt. Steve Katz
See Beyond the Mist
The recent foggy morning weather requires mariners to pay more attention while navigation the ocean or bay waters. Making use of all navigation aids, such as navigation lights, radar, fog horn, and AIS (Automatic Identification System) are best practices that should be followed by all mariners.
Automatic Identification System or more commonly referred to as AIS, is an electronic vessel tracking safety and collision avoidance system used by boats, land stations and some emergency rescue devices.
The AIS system automatically exchanges electronic information about each transmitting vessel with other receiving vessels in the nearby area – about a 20-mile range. AIS signals are automatically broadcast digitally on a frequency of 161.975 MHz and 162.025 MHz from the 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.
When mariners refer to AIS, it is usually in a generic term, since there are many subsets of AIS depending on needs and requirements.
Types of AIS
Receiver
The simplest and least expensive AIS device is an AIS receiver. This is electronic hardware installed on your boat that allows you to receive an AIS signal broadcast from a nearby vessel or transmitter. This receiver could be specialized stand-alone hardware with or without a screen.
The AIS data is often displayed in a visual format, either text or graphically overlaid on a navigation chart to inform the captain of the name, location, speed, heading etc. of nearby vessels transmitting an AIS signal. Since the AIS system uses radio frequencies within the marine VHF radio spectrum, a marine VHF antenna can be shared with an AIS receiver, though an independent AIS independent is best.
There are modern VHF radios that can receive AIS signals and can be optionally integrated into a chartplotter to provide an enhanced graphical representation of nearby AIS vessels.
Transmitter
The more complex AIS device is a transmitter, a specialty stand alone device that will automatically transmit pre-programed and variable data about your vessel to AIS receivers. There are many categories of AIS transmitters due to needs detailed in USA and international maritime regulations. Most, if not all AIS transmitters also receive AIS signals, and is referred to as a transceiver-, a transmitter and receiver in one unit. Some manufacturers refer to their AIS transceiver as an AIS transponder, like the term used for aircraft. An AIS transmitter has special regulatory requirements, including guidance by the FCC that the hardware is to be programmed or re-programed by a marine electronics technician and not the end user.
An AIS transceiver requires 2 antennas; a dedicated GPS antenna and a dedicated VHF/AIS antenna to transmit the signal.
Features
Many recreational boaters 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 the location of other vessels is a helpful collision avoidance and safety feature. Reading the other vessels AIS data, you can see the a vessels name, radio call sign, MMSI number, location, speed, heading and more information, depending on the type of AIS system used. An often-unused feature is that an AIS receiver allows you to see the nearby vessels MMSI number. Using this MMSI number, you can make a DSC (Digital Selective Calling) direct call to the other vessels' marine VHF radio, if their VHF is properly programmed. This feature is great in a situation where you need to contact another ship’s captain and let them know where you are located or ask about their navigational intentions.
Using an AIS receiver is like spying; you can see and read about the boats around you, but they do not know you are listening. Fortunately, recreational AIS transceivers have an optional switch that allows you to temporarily disable transmission of your AIS data, for example when fishing in a tournament and you do not want your competitors to know where you are!
Costs
AIS receivers as a built-in feature on VHF radios adds about $100 to the cost of the radio. Standalone AIS receivers, relying on an existing chart plotter and sharing your VHF antenna, begin around $300. If you really want to be “seen” in the AIS environment, you will need to install an AIS transceiver that can transmit your vessel's data. The hardware costs begin around $800 for a class B transceiver. An AIS transceiver is required to have its own GPS antenna and its own AIS/VHF antenna for broadcasting and receiving. The processor box is programmed by a technician with the ship's static data, such as: vessel name, radio call sign, MMSI number, vessel type, vessel dimensions, GPS antenna location etc. An AIS receiver or transmitter often needs to be connected to your chart plotter using NMEA 0183 or NMEA 2000 to send the AIS data so it can be seen by the captain on the screen.
An AIS is a great situational awareness tool for any mariner operating a boat, especially during times of limited visibility. §
