What is Marine AIS? and How it Could Safe Your Life.

Collision avoidance at sea has to be the number one, top priority for any mariner.

And while radar is still the best known and most comprehensive aid to visibility and collision avoidance on the water, AIS comes in a strong second and in some cases, might even be considered more useful than radar.

What is AIS?

AIS stands for “Automatic Identification System,” which is global tracking system for vessels which actively transmit a signal from AIS  transponder. This signal not only includes the vessel’s location, but a wide range of of additional information as well such as speed, course, size and name, origin and destination, etc etc.

Most large commercial vessels, and all passenger vessels are required to have AIS, and increasingly, many smaller recreational boaters are choosing to transmit AIS as well.

AIS is transmitted through VHF radio signals and satellite networks, and are received by AIS receivers. Many marine VHF radios have AIS receiving capability as well, and when paired with a chart plotter, can overlay AIS information directly onto your chart plotter screen.

Operation.

My system uses a Standard Horizon GX - 2150 VHF radio as an AIS receiver, which is paired to a Lowrance HDS Live MFD, which allows for various settings on how the AIS signals are displayed, and different alarm configurations as preferred.  AIS equipped boats on my MFD show up as boat outlines, and the ones that are underway also show an customizable “target extension line” off the bow which gives a visual on course, speed, and potential point of intersection.

This photo of my MFD screen while tied up in the marina shows my boat as solid black arrow (top center). Other boats tied up  in the marina transmitting AIS signal can be seen as boat-shaped outlines (right). This marina is chock full - so while all the slips are occupied, you only see the boat outlines where there is an AIS transmitter.

The yellow boat shaped outline in the grey circle (left) shows a vessel underway on the adjacent river. You can also see the target extension line (dotted line) coming off the bow showing course and speed. This line can be set to a certain distance ahead of the vessel (e.g. a mile ahead), or a time based projection of where the vessel will be after a specific duration, such as 5 min.

See video below showing real life examples.

AIS vs RADAR.

There are essentially two main practical differences between AIS and Radar.

First, AIS only displays vessels that are actively transmitting an AIS signal, so you will see a lot, but not all vessel traffic.

As AIS is essentially mandatory on all large commercial vessels however, this basically means you will see all the big freighters, ferries, tankers, tugs etc. in your vicinity. In other words, everything that is big enough to mow you down without even noticing should be transmitting an AIS signal. More and more pleasure craft are also choosing to add AIS transponders for increased visibility as well, but as most boats under 25’ are not equipped with AIS transponders, they will not be visible.

What AIS does show however, is clear and easy to read. I also find the target extension lines extremely useful especially when I am fishing, even on clear blue days. At trolling speed, when my attention is often more focussed on fishing than traffic avoidance, seeing the dotted, target extension line of an approaching vessel appear on the chartplotter, especially coming from behind is a terrific advance notification.

Also, being able to see boats around blind corners and points, as well as as their course and speed really makes traveling safer.

Finally, if you choose to add a full AIS transponder, rather than just a receiver, you can also transmit your vessel information, making yourself visible to AIS equipped vessels.

See how AIS works in real life.

Radar on the other hand, reads signals reflected off actual objects. So a boat does not need to be transmitting anything to be seen by radar. In theory, that means if it’s there, you should see it on your radar screen. Similarly, in theory, a radar system should also be able to detect your boat as well without you having to transmit anything.

However, radar has its limitations, and especially in rough seas, civilian radar can often miss small boats.

Reading radar screens like this one can be tricky and confusing for the inexperienced user.

Furthermore, for the non-professional boater, there is definitely a learning curve to reading radar signals, which can be difficult to interpret.  In practice, if you only turn on your radar once every year or two when you get caught in fog, its likely you won’t be much better off, as you probably won’t know what you’re looking at anyway. Travelling in low vis is difficult and stressful at the best of times, so being glued to your screen trying to learn to interpret your radar signals at the same time might even make matters worse.

Bottom line.

Most of time, plain old vigilance, paying attention to where you’re going, knowing the rules of the road, and basic navigational and boating competence will keep you safe.

But marine conditions can change rapidly. Fog banks and heavy rain squalls can seemingly come out of nowhere sometimes and navigational aids like radar and AIS can be lifesavers.

Having the ability to run both radar and AIS together is of course the ideal situation. Adding a radar system however is a significant investment, which many recreational boaters would have a hard time justifying.

Adding AIS capability to your nav system however, is relatively inexpensive, and there is no learning curve involved. Whether you choose to do this through your VHF radio, an AIS receiver, or even a full AIS transponder which will also enables you to transmit your vessel information, it is a mere fraction of the cost of adding radar. In fact, you can even get near real time AIS information on the MarineTraffic phone app, which has a free version, although you do need to be in cell service or online (see video here)

Sometimes known as the "poor man's radar," adding AIS capability to your nav system to me is a cost effective, no-brainer for the significant added layer of safety and peace of mind it provides. And no, it's not radar, but even radar has its limitations and downsides. AIS is cheaper, easier to use, and it might even save your life one day.

.

RADAR is of course the best known aid,