AIS on the cheap, Navagear-style!

[It's another MadMariner feature from a few weeks back. —Tim]

If you’ve spent any time around major commercial ports or vessel traffic lanes, you’ve probably wondered about all those big ships. What’s in those enormous vessels? Where are they coming from? Where are they headed? How fast are they going?

It turns out that the big ships broadcast answers to all of those questions, all the time. To receive that data, you need an "Automatic Identification System," or AIS receiver. You can learn a bit about the technology over at the U.S. Coast Guard’s Navigation Center site.

I’ve had AIS aboard my boat for two years now, in one form or another, and I’m here to say: I would not be without it. I navigate the sometimes crowded waters of Puget Sound, Admiralty Inlet, Rosario Strait, and the San Juan Islands, and it is extremely handy to have access to accurate data about the shipping traffic displayed right on the chartplotter.

[Image generated with Rose Point Coastal Explorer]

Much of the time, to be honest, the AIS data provides a form of entertainment; it’s fun to learn the ships’ names, see how long they are, how fast they’re going and the rest. Recently, however, I was out in heavy fog, and obtaining accurate information about the commercial traffic satisfied a need far more compelling than mere curiosity.

UNDERSTANDING AIS

I’m actually surprised that more boats don’t have AIS receivers, because you can add AIS data to your chartplotter for about $300. About half the time, I get blank stares when I mention it to fellow boaters, and I get the impression there’s still a good deal of confusion about the technology.

To begin with, let’s clarify something: For most pleasure boats, the most valuable aspect of AIS is being able to receive the data big vessels transmit. Transmitting data about your own vessel is, at this point, is not especially helpful. So it’s important to draw a distinction between simple AIS receive-only units, which can be purchased for less than $200, and the more expensive Class B AIS units, which cost about $1,000. Class B units receive AIS data from other ships, but they also broadcast similar data about your boat.

I currently have one of Shine Micro’s Class B AIS units installed aboard Two Lucky Fish, and I like it. But the fact is that nobody really cares where my boat is; the vast majority of the boats in a position to do anything about the position of my boat (or care) are not equipped to receive the AIS data I’m broadcasting. The big ships are equipped to see me, but they’re not going to navigate around me anyway. It’s up to me to stay out of their way.

My point is that about 99 percent of the real-world AIS utility I have experienced so far comes from reception: I know the names, positions, headings, and velocities of the big traffic I need to avoid. I have made active use of this data on several occasions, hailing them by name over VHF channel 13 (the bridge-to-bridge channel most big ships monitor), in order to clarify intentions in passing and crossing situations.

 

BETTER TO RECEIVE

Here is an example from one recent foggy morning. I was arriving at Friday Harbor, on San Juan Island. It’s a harbor I know very well, but in the fog, it was mysterious and frightening. Big pink radar blotches on the screen are certainly nice, but they’re a lot more helpful with AIS vector triangles overlaid on top, especially since you can click on the target and learn the name of that specific vessel.

As I arrived at Friday Harbor, one Washington State Ferry was departing and another was arriving. I never saw either vessel. Heck, I never saw the headland I had just rounded. It was extremely reassuring to see the AIS data confirming the radar data, and to be able to hail one of the boats by name to clarify what they were going to do. I learned that they intended to pass one another right about where I was. Guessing that they would probably give one another a somewhat wider berth than they might in clear conditions, I decided to scoot in and hug the shore pretty closely. That’s about the time I grabbed this screenshot off my chartplotter.

Certainly, I didn’t need AIS in any of the situations where I’ve made active use of it; I could just slow down and wait to see how each situation developed, or take the longer, safer route that keeps me outside the area where the conflict could occur. But it’s empowering and, frankly, just good seamanship to know how to make contact with a bigger vessel, state your question briefly and clearly, and make a decision based on what you are told. AIS allows you to contact commercial vessels quickly – by name – to obtain additional information and confirm that events are proceeding according to your new, more complete understanding of the situation.

THE CHEAP WAY

So let me explain how you can add AIS data to your chartplotter inexpensively. One of the cheapest AIS receive-only units is Milltech Marine’s single-channel SR161. This bare-bones unit sells for $189, but the fact is that it works, and it does what you need to obtain the benefits I have described. To make it work, you need to connect it to three things: a 12-volt power source, a VHF antenna and a chartplotter.

The power is easy. The VHF antenna is fairly straightforward, if you have a separate antenna for it. You’ll probably need to track down a connecter or adapter to get it all hooked up, and that can be a bit of a hassle because standard VHF antennae tend to use PL259 connectors and AIS units seem to favor the BNC adapters. Don’t panic, but don’t be surprised if you have to call around or order online to get the adapter or connector you need.

If you want to share your existing antenna between your VHF radio and the new AIS unit, you’ll need an antenna splitter that can protect the AIS unit from the destructive potential of VHF transmissions you make when you key your mic. That kind of power can damage or destroy a radio receiver, which is one reason I prefer a separate, dedicated antenna for AIS. The cost (new antenna versus antenna splitter) is about the same, but you can often find inexpensive VHF antennae on Craigslist or at marine swap meets, so it can actually be cheaper to add a new antenna. I got mine for $20. Ironically, the antenna mount cost almost twice that. I had to get the fancy stainless steel model.

All that’s left is to connect the AIS unit to a chartplotter, or a PC running navigation software. The AIS-to-chartplotter connection can be a bit tricky, I’ve found, and it varies a lot depending on your chartplotter. I won’t pretend
to cover every angle, but suffice it to say that in the end, you’ll need to connect three wires from the cable that plugs into the SR161′s 9-pin jack to three wires in a NMEA cable you can plug into your chartplotter.

Connecting it to a laptop, however, is very straightforward, even though the SR161 comes with that old-fashioned 9-pin RS-232 connector and your laptop probably supports USB only. All you need is a Keyspan USB-to-serial adapter, which sells for about $25. There are other brands out there, but the Keyspan seems to enjoy a great reputation, and I know from personal experience that it works, though it occasionally will require a reboot (unplug it from your computer, wait a few seconds, and plug it back in).

If you decide to try it with your laptop, let me suggest that you install Rose Point Coastal Explorer. I really love the powerful way it displays AIS data on the chart, so underway I’ll often run Rose Point on the laptop, right alongside my Raymarine chartplotter. I’ve got my installation set up so I can plug the AIS into my Raymarine C-80 chartplotter or my laptop.

Either way, I never leave the dock without AIS. It’s too valuable to me. I think many recreational boaters would agree, if they had a chance to experience it for themselves the way I have. The fact that can be added so cheaply makes it a pretty easy decision, in my opinion.