Article by Capt. Steve Katz
AIS – See and Be Seen
The Memorial Day holiday weekend marks the beginning of the summer season, boaters will crowd the waterways and maintaining safe navigation awareness is even more important on busy waterways.
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 electronically exchanges information about each transmitting vessel with other receiving 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 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
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 a 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, often an existing marine VHF antenna can be shared with an AIS receiver, though an AIS independent antenna is best. There are some VHF radios that can receive AIS signals and can also be integrated into a chartplotter to provide an enhanced graphical representation of nearby AIS vessels.
The more complex AIS device is a transmitter, a specialty standalone 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, therefore a boats AIS transmitter can be the sole source of all AIS communications, in this case the AIS device is called an AIS transceiver, a transmitter and receiver all-in -one-unit. Some manufacturers refer to their AIS transceiver as an AIS transponder, like the terms used for aircraft. An AIS transmitter has special regulatory requirements, including that the hardware be programmed by a marine electronics technician and not the end user. Additionally, this setup requires 2 antennas; the AIS transmitter is required to have a dedicated GPS antenna and a VHF style antenna.
Features
Many recreational boaters receive AIS signals but do not broadcast. This allows them to “see” other vessels; similar to 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 other vessels AIS data, you can see the other 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 of AIS is that an AIS receiver allows you to see the nearby vessels MMSI number. Using their MMSI number, you can make a DSC (Digital Selective Calling) direct call to their marine VHF radio, if in fact their VHF is properly programed. 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 a little like spying; you can see and read about the boats around you, but they do not know you are listening.
Costs
AIS standalone receivers are available at a reasonable cost and available as a built-in feature on some VHF radios. A standalone AIS receiver needs to be connected to your chart plotter using NMEA 0183 or NMEA 2000 to transfer the received data so it can be seen by the captain. Standalone AIS receivers, relying on an existing chart plotter and sharing your VHF antenna, begin around $250. VHF radios with built-in AIS receivers and graphical displays start around $500.
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 $700 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.
More details next week on the different classes of AIS transceivers and the new emergency AIS transmitters. §
Until then, as always...
Stay Grounded!
