Originally Posted by
John Hayward
Hi All,
I just typed an email responding to a friend about my AIS setup and my experiences with AIS on a recent 1000 nm trip down the coast, half of which was singlehanded and thought some of people thinking of participating in the 08 transpac might also find it interesting. I couldn't include the screenshots I mention in the email, but would be happy to send them separately to anybody that would like them. They are about 250K each. I hope this is an appropriate use of the forum and some find it interesting.
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Hi Chris,
I can't tell you a great deal about AIS, but here's what I do know. I copied the rest of the crew of Encore in case they might find this interesting too.
AIS (Automatic Identification System) is required on all commercial vessels over 30 gross tons. It is simply a short text string transmitted on one of two discreet VHF frequencies. It contains (if the vessel has filled in everything) the name of the vessel, MMSI number, position, course, speed, cargo, destination, length, width, draft, rate of turn and several other fields that I am not thinking of. More than half of the vessels that I encountered had MMSI number, position, course and speed and nothing else. This however is the collision avoidance information.
I have a Nobeltec receiver (I am sure they don't make it) that cost about $400 (this is a huge rip-off, but also a supply and demand thing so prices will come down dramatically as this catches on). It listens to one frequency for a while and then listens to the other for a while and goes back and forth. Nobeltec also sells one for about $900 that monitors both frequencies all the time. Having used the one I have, it is adequate for most things. I did notice that it takes longer to get all the information on a vessel and sometimes the vessel will disappear because the string hasn't updated frequently enough because the receiver is changing frequencies. It always comes back, and if this disappearing causes you a problem, you are *way* too close. It usually only disappears when it's a ways away too and so you have weak signal to contend with there also. I have my dedicated VHF antenna on the stern rail, so even seas can block the signal sometimes. As with all antennas, the higher the better, but since you are not concerned about vessels 100 miles away, it doesn't really matter and might only add clutter, not useable information. In LA harbor, for instance, you might have trouble getting a full string from any ship because there are so many transmitting at the same time, they walk on each other?? My receiver, or any receiver for that matter, will only receive and decode the string. The output then has to "go somewhere." I am using the Nobeltec VNS (Visual navigation Suite) chart plotting software on the laptop. Sooo, I have the output from a Garmin GPS receiver and the output from the AIS receiver feeding into the laptop. The software is OK as a chart plotter, although very expensive, but interfaces with the AIS receiver very nicely. I have included screen shots of the display from my "close encounter" and Santa Barbara Channel where I had ships in front of and behind me.
I think that only now are the built in chart plotters starting to include the capability to interpret and display the output of an AIS receiver. I wouldn't buy a chart plotting program or built in chart plotter without that capability!!!!!! There is a stand alone unit available that has the AIS receiver inside a "radar" display and requires only power and a GPS input. It just shows you in the center and the targets around you. I don't think it displays any of the other AIS information and I don't think it has CPA (Closest Point of Approach) and TCPA (Time to Closest Point of Approach) and I don't know if it has an alarm function.
Things to look for: I think the things that are Critical are that it go to a chart display with you in the center, it have CPA and TCPA with a settable alarm function. It is also nice to have the ship information, specifically course and speed. The name of the vessel (if they have filled this information in) is also very handy in case you want to hail them on VHF, you can call them by name. I have mine set for CPA of 2 miles and TCPA of 15 minutes triggers the alarm. This is pretty conservative, but since I am using it so I can sleep singlehanded (I set my alarm clock to go off every two hours for a look about when coastal cruising singlehanded also), I want time to clear the "fuzzies" and watch it a little and still have time to call or change course as appropriate.
The big disadvantage of the laptop is the power consumption and the fact that if you lose your laptop, you lose AIS capability. The drawbacks to the Nobeltec VNS software are that it is expensive, requires a Dongle in the USB port to operate (with international charts anyway) and I find using it for navigation a little cumbersome, not bad but....... The AIS portion of the software is generally great. My only complaint here is the alarm. It gives two funny little blasts and then stops. I would like to be able to set it so the alarm goes off until it's reset manually from the keyboard or mouse. When I am trying to sleep, I have some external amplified speakers attached and this helps. I want to be sure the alarm wakes me since it only goes off once. I am going to email Nobeltec and suggest they incorporate this in future revisions to the software. Just FYI, I am not particularly interested in a stand alone chart plotter. I don't want or need it on all the time, especially open ocean. I turn on the handheld a couple of times a day to check position and that's all that's needed. If I were cruising the intercoastal waterway or going way up the Sacramento River routinely, my feelings would be different. The only time I leave the chartplotting software on is when I'm in the fog or when I'm trying to sleep.
As a side note, I think that in the fog, watching the AIS display is far more likely to help you avoid a collision than standing a conventional watch. In my "close encounter" with NYK Athena 100 miles offshore (one of the attached pics shown after I altered course 90 degrees port), I would have never seen it until it ran me over at 24.5 Kts. Before I altered course, I saw the closest point of approach as 55 feet at one point. Athena was 985 feet long and 131 feet wide, this could have been ugly (for me anyway). I would have heard the fog horn but couldn't have told where it was coming from until it was tooooo late. With coastal cruising, you probably need a conventional watch because of smaller vessels such as yourself that could be out tooo?
This might be more information than you wanted, but I am now a *real* believer in AIS and I think that all cruising vessels who have it feel the same way. BTW - I got the software and AIS receiver at the Strictly Sail Show this year. They had a show package where if you bought the software and the AIS receiver you got the chart area of your choice free. I chose the chart package that goes from Pt. Arena to the Panama Canal.
John
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