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5Raymarine Dragonfly 7 PRO
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Marine AIS

Marine AIS, an acronym for Marine Automatic Information System, is ship collision avoidance technology, which has been required on large commercial ships since 2002, that has finally trickled down to recreational boaters.

Automatic Information System (AIS) is similar in function to the mandatory collision avoidance system carried on airliners. Simply put, every airliner in the sky talks to every other airliner using data streams that broadcast and receive information about aircraft position, speed, and altitude. If the system detects an imminent collision threat it sounds an alarm and advises the pilot on evasive action.

The marine collision avoidance system, AIS, is far less sophisticated and is currently only mandatory on ships over 300 tons and certain commercial passenger vessels.

How It Works

The system uses VHF radio frequencies to transmit and receive a wide variety of static and dynamic information about a vessel. The components of each system vary, a basic system includes a black box transceiver, which can be an actual black box or hardware located in the antenna or display.

You’ll also need a display; it can be a dedicated AIS unit of data can be fed to the same MFD you use as a chartplotter and fishfinder. Another mandatory component you’ll need is an antenna, on some systems a regular VHF antenna will suffice; on others you’ll need a dedicated AIS antenna. GPS data is used by AIS to supply dynamic ship data so most systems will require the installation of a dedicated GPS sensor.

What Class?

Marine AIS units are separated by class. Class-A AIS units are mandatory on large commercial ships. These units transmit and receive data streams over VHF frequencies that keep other vessels and shore based traffic centers informed of certain information about the ship. Class-A units have a maximum VHF power output of 12.5-watts, have the most stringent data update requirements, and are the most expensive.

Class-B transceivers are designed to provide a similar service, at a far lower cost, for smaller vessels that are not required to carry a class-A unit. This is one type of unit of interest to recreational boaters. A class-B unit transmits a smaller number of data fields at a slower rate using a 2-watt transmitter. The majority of class-B units on the market these days are priced between $400 and $2000, depending on capabilities and how many accessories are included.

One other product of interest to the recreational boater is a receive-only AIS unit. As the name implies these units only receive data from other ships and display is for the user to see. No data on your vessel is transmitted.

Data You Need to Supply

Before you can use a class-B marine AIS unit you’ll need to input some information about you and your vessel. FCC regulations require this be done by the maker or a dealer prior to shipping. In any case, you’ll need a valid MMSI number associated with the vessel onto which the AIS will be installed. You’ll also need to supply a vessel name, which can be up to 20 characters in length, a radio call sign if you have one, your boat’s length and beam in meters, and your vessel type. Operating an AIS unit without proper vessel data can result in a fine as high as $25,000.

Marine AIS Antennas

An AIS transponder uses both GPS and VHF signals to function. This means the transponder will need to be able to receive GPS signals and both transmit and receive VHF signals. Some AIS units will ship with its own GPS sensor. As a user you’ll need to mount the GPS antenna in an area with a clear view of the sky and connect it to the AIS unit.

Most units we’ve seen do not come with a VHF antenna. Since this is a required part of an AIS system you’ll need to have one. Some makers recommend an antenna specifically designed for AIS use while others make no specific recommendation. According to information supplied to us from a variety of industry sources nearly all AIS units will work just fine with a standard VHF radio antenna, there are however a couple exceptions, so our recommendation is to follow the guidance of the your specific AIS manufacturer when outfitting your unit with an antenna.