Article by Capt. Steve Katz
AIS- See and be Seen – Part 2
Following up from last week’s column on AIS systems, this week we review different classes of AIS transceivers and the new emergency AIS transmitters.
AIS transceivers (transmit and receive) are currently available in three classes; Class A, Class B, and newest Class B+. Class A transceivers report their position autonomously every 2-10 seconds dependent on the vessel’s speed and/or course changes (every three minutes or less when at anchor or moored); and 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. The class A transceivers are usually found on regulated vessels and have a much higher cost than Class B or B+ AIS hardware designed for less regulated vessels and recreational use.
Class B AIS transceivers operate with less transmitting power and provide the vessels data report less often. Class B AIS broadcast 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 significant difference on how far away you receive data, the specific data your system receives and how often you receive it.
A new regulation a few years ago allowed for a new, third AIS system, fitting in-between the two current offerings. This is sometimes referred, Class B+, Class B SOTDMA or Class B 5W. Why is this new offering important? The Class B+ has over twice the transmit power and range of the original Class B, 5 watts which doubles the transmit range to 10-15 miles. Most importantly for sportfish vessels, the Class B+ uses the same technology of the Class A AIS for sending messages – it has the same top priority when it comes to reserving a transmission time slot in the AIS airwaves, guaranteeing that it will always be able to transmit, even in busy AIS congested waters. For fast moving boats, this is important as a missed Class B transmission can result in a vessel moving a long distance before it next manages to send a transmission.
Are you wondering how this AIS data will be used while we are out on the water?
When properly connected, most chart plotters will show you a triangle on the chart plotter display screen representing the AIS vessel, along with more detailed information when you select that vessel. 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 trying to make radio contact, your AIS transceiver allows you to be confident that the other boat captain can see your ship's position on their electronic navigation system. Commercial captains are usually required to contact other vessels to determine if they are going to alter course or stand-on, and this information is recorded on their VDR (Voyage Data Recorder), mandatory for many large vessels.
Worried that during 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 for Emergencies
Most offshore captains and crew are familiar with the traditional Emergency Position Indicating Radio Beacons (EPIRBs) and Personal Locator Beacons (PLBs) These modern devices work by transmitting an emergency digital signal to an orbiting satellite. The orbiting satellites relay the distress call to ground stations and therefore the time from distress to rescue could be longer that desired. One way of shortening a response time is for the EPIRB or PLB to additionally transmit an emergency signal on the AIS radio frequency. This signal is received immediately by nearby vessels equipped with AIS receivers and that vessel could respond to the distress. There are a few of these products available in the marketplace, though there will be a lot more of these combinations units soon to be offered by a major manufacturer – keep an eye out for this innovative product.
A few misnomers about AIS:
Satellite tracking - Traditional AIS does not transmit to satellites directly, only short range on the VHF radio spectrum to local receivers. There are special satellites that are capable of “listening” for and can receive traditional AIS RF signals and relay them to a ground station. Satellite AIS receivers are most often used to track vessels in open water where the ship is far away from an AIS land-based receiver.
Ship tracking websites and apps – Since AIS only transmits a radio frequency signal, AIS cannot transmit directly to the internet. A ground station that receives AIS data can reformat AIS information and send it to a specialized internet website which then graphically represents vessel AIS data for users to see in a web browser or app. The accuracy of the website data is dependent on many factors beyond the control of the vessel or viewer, so therefore this information may not always represent the true status of an AIS vessel.
An AIS system is a great simple addition to your existing navigation equipment and an important navigation tool for collision avoidance and safety.
NOTE – if you are wondering if your vessel is required by the USCG to have an AIS system, you can review the regulations here https://www.navcen.uscg.geName=AISRequirementsRev
Effective from July 1, 2022, the new IMO rules state that vessels under SOLAS regulations will have to fit a new EPIRB with an internal AIS locating signal and an internal GNSS receiver, along with the 406 MHz and 121.5 MHz transmitters, when current devices are due for replacement. Recreational boats and other non-SOLAS vessels can continue to install the EPIRBs permitted under their national regulations, with many countries expected to enforce the IMO AIS EPIRB mandate in one to two years’ time due to the life-saving benefits offered by these new beacons.
Until then, as always...
Stay Grounded! §
