Well, whereas I stirred up a bit of a Class B AIS hornet’s nest yesterday, I may as well keep at it! It seems to me that another repercussion of Class B’s 30 second (at best) dynamic data rate is that the inexpensive “single frequency” receivers are only going to see Class B targets once a minute (at best). I put “single frequency” in quotes because I’m realizing that the nomenclature for these receivers has gotten pretty confused. For instance, when I characterized the EasyAIS receiver as “dual frequency” back in April, I meant that it could listen to both AIS frequencies simultaneously. Now I realize that I was probably wrong about that, though EasyAIS is not exactly forthright about its receiver's specs. The company site calls it a “real 2 channel receiver”, which, when you think about it, does not mean that it listens to both channels simultaneously, and an English install manual I found (PDF here) doesn’t mention reception modes at all. Meanwhile one retailer, YachtBits, also calls it a “double superheterodyne receiver” which sort of sounds like parallel reception on both channels, but another notes that “every few minutes it switches automatically between both channels” (Busse Yachtshop). And Y-tronic, a reliable source in my experience, says that the EasyAIS “monitors both AIS frequencies by alternating between both channels”, further noting that that it is quite well made. Conclusion: I don’t think that the EasyAIS listens to both channels at the same time, and therefore will miss 50% of the AIS messages sent out in its area. I also think that the industry should settle on some terms for these receivers and use them to properly inform customers.
PS, 12/8: It’s good to see that NASA is clear about its AIS Engine: “The unit can receive ships on either the A or B AIS channels. In default setting it alternates between the two channels.” But then in the very next paragraph NASA claims that the Engine outputs to a “NMEA 2000 input.” It absolutely does NOT, and, moreover, I’ve heard that its serial NMEA 0183 output is so flawed that it won’t drive the opto couplers that are a feature of many good multiplexers. Sigh.
This diagram—borrowed from Dr. Andy Norris’s valuable AIS/06 conference presentation—illustrates various possible target presentations for a vessel doing 30 knots over a one minute time period. The green dots roughly represent both radar paints and Class A AIS messages received. (A normal 24 rpm radar would, of course, hit a good target twenty-four times in a minute; a Class A transponder going this speed sends out dynamic data every two seconds, or 30 times per minute.) But the triangular icons indicate what a smaller vessel (possibly a poor radar target) carrying Class B AIS might look like, given B’s maximum dynamic data speed of 30 seconds. Obviously the target could move a quarter mile between plots, making like a mexican jumping bean if your plotter/ECS is zoomed in very far. Now there is an obvious, though processor intensive, way to smooth over Class B’s relatively slow data rate, which is for your plotter or ECS to calculate DR positions for each target between actual AIS fixes. I know I’ve been shown at least one PC-based product that already does this, but I can’t remember which one, and I don’t know if any plotters do DR (in an all-Class-A world it doesn’t matter as much). So please help me—either via comments, or e-mail—build a list of the AIS viewers that do or do not DR targets.
PS 12/7: Well, this DR idea turns out to be much more controversial than I realized. Apparently only Transas, which only seems to sell ECDIS these days, currently does DR calculations on AIS targets, and some developers have serious reservations about adding this ability to their own AIS target plotters:
“My opinion is that a DR feature in between AIS fixes presents some VERY SCARY Safety Concerns. I have heard that this issue has also been raised in the IEC ECS meetings. For example, what happens if the AIS Target you are tracking changes course after an update is received and then an extended period of time elapses before another update to the to the new ship's course and speed are received??? The vessel may have made a course change which was not received by you and you may choose to make a critical navigation decision based on incorrect DR Position information.”
Others feel that, “The DR position is likely to be closer to where the boat actually is than the last actual position which is crucial for collision avoidance. You avoid a collision by anticipating where a boat will be, not where it was 30 seconds ago.” There may be a graphic solution, say changing the color of an AIS target’s “bread crumb” track to indicate fixed and DR positions. I will definitely collect more info and opinions, and share them here.
I think that at least three AIS Class B transponders are now fully approved and shipping in Europe, or darn close to it. And I believe that all three are based on Software Radio’s PCB (below). Interestingly the Comar CSB200 has changed since first pictured here. Note the “TX off” LED; two contacts on the back let the user rig an optional switch that will put this unit in Silent mode. Comar, unlike SevenStar, has not chosen to utilize the optional Safety Related Message (SRM), arguing that even some Class A AIS units can’t read it yet, let alone the shoreside authorities. These are some of the differences possible while still using the same core SRT transceiver. Hopefully, the good people at Trueheading, Y-tronic, Shine Micro, and elsewhere will fill us in on others. The Comar, by the way, was selling at METS for about 600 Euros, plus another 100 for an active GPS antenna, and you’ll need a VHF antenna too (hopefully tuned for AIS). Meanwhile, here in the States I’m told that USCG and FCC approval is still pending, subject to issues concerning “MMSI assignment, full transponder ‘Activation’, exclusive use of AIS I and 2, inland waters, and satellite monitoring, just to name a few.” Sigh.
I may seem hung up on Garmin and NMEA 2000, but actually METS was worth months of future Panbo entries. For instance, the world introduction to the B&G H3000 system and also to Navico, the new “papa” brand over arching Simrad, Lowrance, etc., was wonderfully prefaced by extreme racing sailor Knut Forstad. Besides showing some stunning video of Volvo 70’s (100% B&G equipped), he had this slide illustrating an automatic sheet release system on a trimaran. Those Harkin cam cleats can be pneumatically opened by a Hercules processor based on any parameters in the system, like heel, pitch, wind speed, etc. Nice for a single hander trying to rest at 30 knots plus! After the press conference I asked Knut if offshore racers are using AIS. He told me that the Volvo Brazil picked up a receiver in Baltimore, loved it, and that many of the open 60 tris are now carrying full transponders. He was adamant about how valuable a technology it is, and how every offshore race boat should be carrying one. I learned a lot about AIS Class B at METS, but it will have to wait.
Well, I attended most of the 3.5 hour GMDSS Task Force meeting at NMEA—with USCG, FCC, and other relevant parties present—but I still don’t know exactly when Class B AIS will actually be on the market, especially here in the U.S.A. But I did for the first time put my hands on one, and, surprise, it came from a company I had never heard of. The SevenStar Electronics SeaTraceR Class B AIS is based on a transceiver developed by Software Radio. The engineer who was toting it around said that is has received IEC approval and will soon be on the market for around $1,000. It is set up to connect to a PC with a small program that allows entering the MMSI just one time, either by a dealer or user (one of the issues yet undecided). An interesting feature I did not know about is that SRM Sent LED. Apparently the Class B standard includes the ability to send some sort of distress text message, using a ‘panic’ button connected to the unit. The SeaTraceR can supposedly be reprogrammed so that the button instead activates a Quiet Mode—receiving, but not transmitting—which is an option some users really want. More on AIS soon.
Today I thought I’d see how well the latest 3210 software (version. 2.6) handles input from the SeaCas SafePassage 300 (it’s got a model number now because Fred has added two new versions). The results were better than last time; for instance, the megayacht Floridian, (visiting again), revealed its name and other important info (bigger image here), and the AIS control menu sub tab is available, letting users specify what zoom levels show AIS and whether target prediction lines are based on time or distance (and how much). But I was a little surprised by what’s missing, and asked Garmin for confirmation/explanation:
1) The 3210 does not yet calculate CPAs…”We wanted to see how reliable and accurate the AIS system really was before giving users automated monitoring. We felt it best to not give users a false sense of security if in reality AIS data transmitted by most ships was inaccurate.”
2) It also won’t list targets, a feature that I think I’ve seen on every ECS and MFD that handles AIS. But Garmin’s comment, “Can you help us understand what such a list would be used for?” is interesting. Nothing came to mind instantly (besides hunting for megayachts); I usually do query AIS targets graphically, putting the cursor over one and hitting “enter” for more info (as above, the only way possible on the Garmin).
I guess the good news here is that Garmin is supporting AIS at all. I dare predict that CPA calculations will come eventually, maybe even a target list, especially if you all make a case for why in the comments section below.
Meanwhile, you may wonder what’s up with the rusty coffee can in the background left? That’s part of my testing gear, a GPS signal inhibitor! I was hoping that if I forced the attached Garmin GPS 17 to lose position, the unit might pick up the position being sent by the SafePassage (as is done by the Raymarine E-120, sort of; it gives priority to the NMEA 0183 SafePassge, but will pick up a NMEA 2000 GPS if the SafePassage loses signal). No such luck, even when I totally uninstalled the GPS 17.
This photo shows the AIS receiver test I mentioned a while back. There’s organizer Jeff Hummel of Rose Point Navigation, Doug Miller of Milltech Marine and Cory Sytsma of SeaCAS, plus eight different receivers all set up on the shore of Puget Sound. It would be great to see how they performed head-to-head, but the picture also reveals what turned out to be a significant flaw in the testing. The close proximity of receivers and antennas apparently created an interference cloud so strong that performance dropped 50–75%! For instance, the first unit that was turned on, a single channel SR161, showed a range of 17-20 miles until the others went on and its range dropped to around 7 miles. The crew did go on and collect some results (which didn’t look good for single channel models), but almost none of the manufacturers involved think they should be published. Hopefully the test will be restaged with much greater separation between the units. In the meantime, hats off to Jeff and the gang for the effort. Their work does suggest that we need to learn more about receiver interference and proper installation, and they also did a separate antenna test that we’ll publish soon.
The good folks at Shine Micro sent over an update on their own Class B AIS product, RadarPlus, and the general state of the category:
* RadarPlus really exists, units licensed for experimental use are in the field (right), and test results are “very pleasing.” (Though, no surprise, receiver sensitivity does really matter with these 2 watt units; more on that in September).
* However, “dealer programming of the MMSI is definitely coming for North American users”, and “The FCC can be expected to take a minimum of 4 months to digest all the comments they are receiving on the latest ‘Further Notice of Proposed Rule Making and Fourth Memorandum Opinion and Order’” (in .pdf here).
* Which is why Shine isn’t currently predicting “any date for FCC approval of AIS Class B”, but does “like Comar and True Heading, plan on shipping units internationally in late October.”
I searched through that .pdf above, plus the FCC site, for more on this MMSI/Class B business, but without success. Anyone? It might also be interesting to see who has applied for Class B licenses.
I just got the new Captn. Jack’s catalog, which seems pretty quick given that Maptech just took over the operation a few months ago. The online Captn. Jack’s is also back in business, which means I can link you right through to some of the more interesting offerings:
* The fictional Jack is indeed bundling Maptech Chartbooks with Garmin plotters, as above, including putting all the on-paper waypoints into the plotter. Just the product combinations themselves look like decent deals, the waypoints a very useful bit of frosting. (I’m hoping to try the feature out).
* The Capn software (no previous relation to Captn. Jack, and different spellings retained) has now become CAPN Integra AIS, and there’s some more detail on how Maptech plans to market it. Jack is also selling the U.S. Boating Charts DVD, which I have tried (it’s excellent), both alone and nicely bundled with Memory Map.
Note that Captn. Jack’s is offering free ground shipping and a money back guarantee (though a tight one). Altogether it’s a pretty neat catalog, and probably the one most focused on marine computer navigation, though it still doesn’t thoroughly cover the products available. Isn’t it strange that Captn. Jack’s once offered almost every major ECS except the Maptech ones, and now it features Maptech’s even larger roster but is missing major products like Nobeltec, MaxSea, and RayTech?
I have a great deal of respect for professional seaman, but, like the rest of us, they do screw up. Unlike the rest of us, they are driving very massive vessels. In April 2005, for instance, the container ship Lykes Voyager, en route to Vancouver at 19.5 knots had a fender bender in a foggy Taiwan Strait with another container ship, the Washington Senator, which was Hong Kong bound at 17 knots. “No one was hurt but both ships were damaged and a number of containers were lost overboard.” Imagine the sound! As usual the MAIB (the UK’s Marine Accident Investigation Branch) has produced an amazingly detailed report on just what happened, available in several PDfs. Noteworthy items as drawn from the report by Digital Ship:
* “Using the VHF radio, the master of the Washington Senator had agreed to a starboard to starboard passing arrangement with another vessel that he mistakenly thought to be the Lykes Voyager - he was, in fact, conversing with another unidentified vessel.”
* “The use of the radio as the primary method of communication for a distress call after the collision was also ineffective according to the investigation, as there was no response from any other vessels or from the search and rescue (SAR) authorities.” (They used 16, not DSC!)
* “Even though both ships in this case were fitted with AIS equipment it was not utilised for identification - if it had been the Washington Senator could have easily identified which ship it was speaking with, and the incident could have been avoided.” (Both had only MKDs to track AIS targets, which—in other words—were not integrated onto their radar or chart displays.)
We need to think about realities like these even as we get excited about Class B transponders. And thank our lucky stars that we weren’t in a small boat trying to avoid these behemoths that foggy morning off Taiwan.
hose Harkin cam cleats can be pneumatically opened by a Hercules processor based on any parameters in the system, like heel, pitch, wind speed, etc. Nice for a single hander trying to rest at 30 knots plus!
The good folks at 
