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Tech Talk with SeaBits
SEE AND BE SEEN WITH AIS
by Steve Mitchell
Situational awareness while you are on the water is extremely important, and something we all strive to maintain. Every couple of minutes, I do a “360 check” by looking all around the nearby water and horizon to make sure I know what is around me. Pairing a chartplotter with radar is another great way to make sure you know what’s going around you. Automatic Identification System, better known as AIS, is an additional technology that can help you identify the boats near you, and to tell other vessels about you, and so much more. AIS uses VHF radio frequencies to send out messages on two specific channels. Those messages include information about a boat, its location in GPS coordinates, how fast it is going, its heading, and more. That information is available to anyone within range of the signal, as well as online tools such as Marine Traffic. You can leverage that information by having one or more parts of an AIS system on your boat.
Using AIS to see how close I will pass this oncoming traffic 48º NORTH
WHAT DOES THIS GET YOU? If you have a full onboard AIS system that allows you to transmit and receive, not only will you be able to see all of the vessels around you that have AIS, but they will be able to see you as well. Seeing vessels near you is super helpful, and is one of the main reasons people initially look at AIS systems. Once you have this information on your chartplotter or VHF radio, you will never want to be without it. Not only can you see the name of a ship, which is useful when making a radio call to arrange safe passage, but you can also see its speed, size, and information such as Closest Point of Approach (CPA) and Time to CPA (TCPA). — key pieces in avoiding collisions. Closest Point of Approach shows you how close you will pass the other vessel based on both of your current courses. Time to CPA will tell you when you will be at that closest point. These two pieces of information reveal how quickly you need to do something to avoid a collision, or if there will be a collision at all. Many chartplotters will show this information graphically to make it easier to understand, and you can set up alerts and alarms to let you know when someone is too close or on a collision course. Having this information is nice, but also sending your vessel’s information is even better, and allows everyone else to see where you are, how fast you’re going, and your vessel name. This means that they can use it to avoid a collision with you, or simply hail you accurately on the VHF radio. This has come in handy for me a number of times with commercial traffic who would have not known my vessel name without AIS. PARTS OF AN AIS SYSTEM There are three components to an AIS system: the transponder, which sends out AIS messages; the receiver, which listens for messages; and a display of some sort. If you only want to see other boats, then you need a receiver connected to a display, like a chartplotter. If you want your boat to be seen by others, as well as see everyone else, then you need a transponder. Let’s break down each of these so we can understand a bit more about how AIS works, and the best way to get it on your boat.
28
DECEMBER 2020
