Closing a Central Coast Coverage Gap
Have you ever felt as if you’re being watched on the water in a way that brings you peace of mind — knowing that at any moment someone can see you, track you, and even call for help if something goes wrong?
The automatic identification system, or AIS, allows vessels to transmit information such as their position, speed and identity. Originally designed for larger commercial vessels, AIS has become a cornerstone of collision avoidance, accountability and overall maritime safety. A critical part of the system is terrestrial AIS, which consists of land-based receiver stations installed along the coast that listen for AIS signals transmitted by vessels offshore. These stations provide real-time coastal vessel tracking and share that information with emergency responders, harbormasters and vessel-tracking platforms. But there still isn’t full terrestrial AIS coverage along the coast of California, or coverage from the Bay Area down to San Diego.
There are two main types of AIS transceivers: Class A and Class B. Class A is required on ships more than 300 gross tons, passenger vessels and most commercial vessels over 65 feet. Larger vessels transmit at higher power, more frequently, and are often required to have their AIS data relayed via satellite, in addition to shore-based receivers.
Class B transceivers are used by pleasure craft and smaller vessels and transmit at lower power and less frequently, and as a result, rely heavily on terrestrial AIS receiver stations along the coast for their position data to be received, shared, and made visible online. Without nearby shore-based receivers, Class B signals often go unseen beyond a limited local range, effectively removing these vessels from wider situational awareness. All classes of AIS transceivers transmit their signals over VHF radio frequencies, the same spectrum used for standard marine communications and received by nearby vessels and terrestrial AIS stations on shore, where platforms such as MarineTraffic and OpenAIS receive information.
Terrestrial AIS receivers are becoming increasingly important. They are easy to install and can provide up to 80 nautical miles of coverage, depending on location and antenna height. That coverage is critical in areas where AIS reception is limited or nonexistent. I have been sailing along the California coast for the past five years, either in FJs sailing for the UC Santa Cruz Sailing Team or in a Moore 24 sailing for Team Pegasus. I never thought twice about my ability to call for help — I either had a cell phone signal or was within VHF range. But when I went down to Morro Bay to do a delivery back to Santa Cruz, I discovered a large gap in coverage. There were no AIS receivers between Monterey and Morro Bay, which can be one of the most dangerous stretches of coast. Addressing the problem turned out to be much easier than expected. MarineTraffic was willing to supply the necessary equipment. After a short application and a few emails back and forth with a representative, a kit arrived. The plan was to install the receiver somewhere on the Central Coast.
