SevenStar Class B, & an AIS rumination


I’ve been testing a SevenStar SeaTraceR Class B AIS transponder for couple of weeks now, mostly on Gizmo but also in the lab.  I could not detect any significant performance differences between it and other Class Bs, even when quickly swapping antenna connections and counting targets.  But it does have a nice over/under tilt mount that lends itself to numerous install positions, and it also has wires for a remote silent switch, like the ACR Nauticast B (though, also like the ACR, it has no built-in switch).  I’m pretty much convinced that the first generation Class B transponders all perform similarly (and pretty well), but what will we see when the next generation comes along?…

I’m regularly seeing Class B targets at five or six miles, even with land and other obstructions in between, and my antennas aren’t great.  That sort of raw transmit range — which generally becomes 8-12 miles on open ocean, especially given a receiving ship’s higher and better antenna — probably isn’t going to change, because the 2 watt maximum power is pretty much written in stone.  But, then again, next generation AIS receivers may become more sensitive and hence bring in more distant targets.  Certainly that’s the wonderful trend in communications electronics, along with rapidly diminishing size and cost.  I don’t know how small and inexpensive Class B (or A) can go, but my sense is that we have only seen the tip of the iceberg.
   In fact I had something of an AIS vision while laying in foggy Frenchboro recently.  Many of the lobster boats there carry enormous VHF antennas that, along with the big rigs seen on many roofs, help keep everyone in touch, and safer, during the long work days.  The islanders have also clearly taken to the Web as a valuable way to stay in touch with the world from 8 miles offshore (and promote their sidelines).  How easy-to-own will AIS have to get before this lobster fleet adopts it (and sets up an onshore Web feed)?
   I suspect that there are endless niches like this where AIS will blossom, especially when it gets smaller/cheaper/better.  Check out the screen shot below, which shows the Class A megayacht Silver Shalis towing, or being trailed by, her Class B equipped tender Little Shalis.  Of course that means the big yacht’s skipper can easily track the smaller boat when both are underway or when the tender is zipping around some anchorage. But that’s also means that any of us other AIS receiving vessels can easily suss out what those otherwise mysterious twin radar targets are coming down the Bay.  Just as many of us would benefit if lobster boats — which go, stop, turn this way and that, and then go again most all day long — were also part of the System.  I may be discovering various little glitches in the just begun (but promising) integration of AIS and NMEA 2000, but that’s just the tippity top of a very large iceberg. 


Ben Ellison

Ben Ellison

Panbo editor, publisher & chief bottlewasher from 4/2005 until 8/2018, and now pleased to have Ben Stein as a very able publisher, webmaster, and editing colleague. Please don't regard him as an "expert"; he's getting quite old and thinks that "fadiddling fumble-putz" is a more accurate description.

33 Responses

  1. Richard C says:

    So, lets summarize with a dream sheet for second generation AIS. Here is what I would like to see.
    1. Smaller, 2.NMEA 2000 output, 3.USB connectivity, 4. Both remote switch for turning off TX and a unit mounted switch. 5. Easy programing by end user for vessel status. 6. (add your feature here)
    I don’t know why manufacturers didn’t include N2K and USB on the very first class B models. It was clear during the design phase that N2K was going to replace 0183 and USB 2.0 was already the excepted standard since all computers had abandon the serial port. Why design old technology into a new product? One more thought, how about a $499 price target? At this price you might start to see the lobster boats on your electronic chart.

  2. Ben Ellison Ben Ellison says:

    Good thoughts, Richard, and very doable I think. But #5 only applies to Class A, right?, since Class B does not transmit a vessel status message.
    By the way, I also think that Class A transponders will come way down in size, cost, and complication, and hence will become the choice of larger yachts and many of the commercial boats that aren’t yet mandated to carry AIS.

  3. Sandy Daugherty says:

    When its the size, shape and durability of a hockey puck, it will show up on everything out there, from water taxis and crabbers to sea-doos and swim-tows. Which begs a class “C” device: a prominant on-off switch, 1.5 watt max power and restricted antenna height!

  4. Thomas says:

    My wish list for AIS woud be to one day have very small waterproof units that can be attached to floating obstacles such as dredge hoses and even crab/lobster trap floats. Entanglement issues would go way down of you can see a blip of the floats before you are on top of them (especially at night)!
    I have been using a Raymarine AIS Receiver for the past year and really like seeing what is ahead. I just recently purchased the Raymarine Class B transmitter whichI hope to install shortly.

  5. Ben Ellison Ben Ellison says:

    Incidentally, SevenStar also makes two Radar Target Enhancers (RTEs), called SkyTraceRs…
    something like the EchoMax Active-X discussed last week:

  6. Lee Simpson says:

    How about having the Coast Guard transmit a phantom AIS target at the location of a mayday. This would greatly enhance the S&R process.

  7. Tim Flanagan says:

    Lee, I wrote a manifesto about “artificial: or “synthetic” AIS transmissions back in 2007, and I still stand by it, with minor modifications, now that I’m an active AIS user. Here’s a link to that article:
    And Ben, I have to wonder if the reason all the Class B units seem to function just about the same is that they all use the exact same chipset? That’s my understanding, anyway, but I’m willing to be proven wrong! 🙂

  8. Adam says:

    So does Navico still have the only NMEA 2000 Class B transponder?

  9. If these units all provide essentially the same functionality, can anyone explain the dramatic difference in power consumption between them.
    For example, the SevenStar unit claims (on the specs downloadable at their web site) to consume about a third of an amp at 12 volts whereas the Furuno FA-50 unit draws 2 amps at 12 volts (again, according to the brochure on the web site).
    Why does the Furuno unit draw six times the power as the SevenStar unit????
    Thanks, Bill

  10. Dan Corcoran (b393capt) says:

    I strongly desire AIS transievers to receive (over NMEA 2000 or 0183), the current channel my ship VHF is tuned too and use that to slightly modify my vessel name sent over AIS to reflect that channel (e.g. 09.BreezePleeze vs 72.BreezePleeze) so that nearby ships know which VHF channel I can be hailed on.

  11. Dan Corcoran (b393capt) says:

    Has anyone considered, that with NMEA2000 support, AIS products may need a way to be told which heading source or GPS to use, or for multiple GPS’s what the position of each of multiple GPS’s are on the vessel ?

  12. Ben Ellison Ben Ellison says:

    Dan, my man, you’ve really got to get a grip on what’s possible. Changing AIS to reflect your working channel is not. The international AIS standard already includes a vessel’s name and call sign, making it easier to call over regular hailing channels. Plus it includes every vessel’s MMSI number, making quite possible for boats in AIS contact to direct dial each other on any channel they choose, and get the other target’s attention. That’s plenty good enough.
    Also, Class B AIS transponders must by rule have their own GPS receiver and antenna. Heading data is optional, but if N2K Class B transponders do it in the minimal fashion — i.e. lock on to the first heading PGN that comes over the backbone, roll over to another if the first fails and another is available — is, again, good enough.

  13. Peter says:

    I would love to have a secure WiFi connection for programming boat info.

  14. Dan Corcoran (b393capt) says:

    Ben wrote “get a grip”
    🙂 … do I have to? I like this crusade!
    “The international AIS standard already includes a vessel’s name and call sign, making it easier to call over regular hailing channels.”
    hmm, what channel are you going to hail me on Ben? 9 or 16 or 68, 69 or 72 ? Am I on 69 talking to another boat in my club or need to monitor for a race, or maybe I am on 14 because I was last talking to a ferry and have not switched back ?
    I am a very savy user of electronics, but I am not going to dial anyone with MMSI using the stupid interface on my VHF (which isn’t even available at the helm with the ICOM remote mic), and I suspect it will be over 5 years before 25% of the recreational boats out there will have made their 1st MMSI call.
    I feel there would be a vast jump in safety in passing situations in fog, if I could see the channel the boats I desire to hail is using.
    It might also speed up the adoption of AIS, and bring people back to using VHF rather than cell phones to hail each other.
    Embeddeding the VHF channel in the vessel name ought to be trivial … and understanding trivial can be a really really big deal in this standards body, it might be the only reasonable change that could happen if there was some support. Or maybe, would it necessarily be a violation of the standard if vendors just started doing it ??? After all, USCG said the vessel name is redundant, they will use the MMSI number to research their database on me.
    [In regards to the GPS, I had forgotten about the dedicated GPS, but then that brings up another feature idea, in an N2K capable AIS … it could be helpful if the AIS transmits all the PGN’s associated with it’s GPS.]
    Anyone out there ready to join my crusade 🙂
    09.BreezePleeze over and out

  15. JonM says:

    I’m still holding out for the VHF radio with integrated Class B AIS transceiver (and both NMEA 2000 & 0183). Reps from two of the big manufacturers told me that they were coming. That solution would nicely solve antenna issues, provide GPS data to the radio, and be a simple installation.
    For now, we have a SR161 connected to an E-80.
    Recently, we started getting some sort of pop-up AIS alerts on the E-80 that seem to be AIS tests. In one case, a second message of “THANKS” arrived after we cleared the alarm. Obviously we did not send a reply to the requester with the receive only SR161.
    I don’t see anything about this sort of message in the basic Class A and Class B AIS data fields.
    While looking for the Raymarine E-80 manual PDF tonight (to explain the above), I stumbled across another PDF I downloaded some time ago entitled “St Lawrence Seaway AIS Data Messaging Formats and Specifications” which specifies messages about weather conditions, names of vessels in locks, etc.
    So, it seems that custom AIS messages are possible. Maybe Dan can set some standards for the hailing channel idea.
    In the meantime, I still don’t know what those “AIS Message / Alerts” observed on Sundays in the upper Chesapeake are. Too bad I was not logging AIS data to a PC at the time.
    Jon M

  16. Roger says:

    You will be aware that calls on DSC VHF settle the issue of “which channel?” as the caller designates the channel to be used for subsequent voice communications.
    In Europe, unlike the US, the vast majority of vessels are equipped with DSC and whilst DSC is not as slick as initiating a call on voice, it is more reliable and commercial shipping monitors DSC whilst they do not have to monitor channel 16 (though many do).
    I agree though, I’m all for simple.

  17. Dan Corcoran (b393capt) says:

    Roger wrote “You will be aware that calls on DSC VHF settle the issue of “which channel?” as the caller designates the channel to be used for subsequent voice communications”
    Thanks for keeping the thead alive!
    Yes, certainly correct from a functional point of view for people who would use the DSC feature in the VHF to make calls.
    But that isn’t happening now, and I don’t think it will be happening in more than 20% of recreational boats even 4 years from now, and perhaps almost all of those will happen because of new DSC user interfaces up to and including a feature to crosslink VHF radio / AIS / chartplotter so you can click on the AIS target.
    In addition to being easier I think a vhf channel in vessel name feature would speed the adoption of AIS and give stronger reason for purchasing transievers vs. receiver only products.
    My predictions of DSC and AIS acceptance from my cruising club of 80 members over the next four years.
    # members that do more than daysailing with their boats.
    2009= 78, about the same each year
    # members that travel to ports more than 50 miles from our harbor annually
    2009= 60, about the same each year
    # members that have an MMSI number in their VHF radio, connected a GPS, and did everything necessary to use the full features of the red DSC distress button
    2009=1; 2010=2; 2011=3; 2012=5; 2013=10
    # members that would have made more than 5 DSC calls from their radio in one season,
    2009=0; 2010=2; 2011=4; 2012=4; 1013=5
    # members that would have made more than 10 DSC calls from their radio in one season, be equipped to use it from their helm (handhelds count), and fluent enough with it to use it effectively in crossing situations in fog (e.g. choosing an mmsi address from a drop down friends list dosn’t count)
    2009=0; 2010=0; 2011=0; 2012=1; 1013=2
    # members who install AIS
    2009=0; 2010=3; 2011=5; 2012=7, 2013=10
    # members who would install AIS if the feature of showing the VHF channel in vessel name available next spring (with new VHF purchase)
    2009=0; 2010=3; 2011=9; 2012=12; 2013=15

  18. Ben Ellison Ben Ellison says:

    Dan, Of course I would try to hail you on 16, the international calling channel. That works for me most of the time. Commercial vessels seem very consistent about monitoring 16, and so do a lot of yachts. Many radios will prioritize 16 when scanning.
    In fact, I used Class B a couple of weeks ago to call a yacht about four miles away (and over a large island) because I wanted to know the visibility conditions where he was (and double check that he was B). “Any vessel on Jericho Bay, please respond” might have worked, but this boat came right back on 16, we went “up one” to 17, and I learned the conditions at his location, which I could see on my plotter. (He was using an ACR Nauticast B).
    At any rate, I don’t understand how you think it ‘trivial’ to change the software in all AIS transponders, let alone imagine that the IMO would consider such a thing in order to promote a style of vessel-to-vessel communications no safety organization has ever advanced before. The chances of such a change are zero.

  19. Patrick Harman says:

    Ben, thank you for keeping us informed about the status of class B AIS. My current boat has AIS receive only. It has allowed me to see that Washington State ferries are around the corner. I am presently commissioning my new boat and it will have a class B AIS.
    It is arcane to use an RS-232 output. I would prefer a USB output. I consider the products on the market today to be works in progress. The future promises much lower pricing and easier connectivity.
    For me the ability for the big guys to know I am there will give us both an increased level of safety. The price point now is less than $1,500 and falling.
    Again thanks Ben.
    Pat Harman

  20. Russ says:

    Integration of the VHF with the AIS so calls are made via DSC without having to use the VHF’s universally bad DSC interfaces will resolve this discussion pretty fast. After that, we should be monitoring 16.

  21. Dan Corcoran (b393capt) says:

    If zero chance, then I suppose I should quit. BUT, just want to share what I was thinking so you don’t think I am crazy.
    Perhaps I should be monitoring 16 more than I do, BUT I suspect I am not unique in having one radio and having reasons to be on 9,14,68,69,72 including having reasons to stay on a channel a while (e.g. race committee), and am not unique in being forgetful to switch back to 16 or not making use of my scanning feature.
    Also, in fog I find people splitting between using channels 9 and 16 in passing situations for example near block island, and some localities seem to have some kind of standing agreement to use other channels in fog and it takes a while to discover that .. again making hailing others really difficult. If just one person in the local area had this vhf channel on vessel name feature, that would help me tune in quickly as to where to find everyone conversing about passing situations.
    I have tried using a handheld simultaneously just to listen to 16, but found jugglng a second unmounted radio not ideal even with a bluetooth headset.
    Also, in fog situations especially, it’s an issue when people leave the transmit button pressed, causing 16 to be unusable, like on my trip to Nantucket.
    In regards to Trivial. Yes, trivial was the wrong choice of words, especially if the AIS is not built into the VHF radio.
    In general I am thinking that if VHF radio’s could send a message out over 0183 or 2000 when the vhf channel is changed, or once every minute otherwise, the software modification in future AIS products are trivial to listen for the message and alter the vessel name stored in memory, and after 120 seconds of no message, to remove the channel number and restore the vessel name as is.
    Such a 0183 message would be very simple, such as $VHF,16. Ge really fancy and include the volume and it becomes $VHF,16,5 so that the AIS can disregard if the volume is set to zero.
    2000 could be simple also, if the PGN is kept simple and seperate from efforts to tackle VHF radio control NMEA-2000, such as allowing a chartplotter to send an MMSI number to call another vessel. Attn NMEA committee, include the volume and maybe squelch level also, so the chartplotter can warn the user attempting to make a call, that their VHF volume is turned down to far.

  22. Furuno Tech says:

    Regarding the Furuno FA50 Power Consumption complaint:
    The 2.0 Amp rating is the peak current consumption at the minimum voltage input of 10.8 volts DC which only occurs momentarily during an AIS Transmit Burst. Furuno always specifies the peak, worst case values so that Installers can specify a proper system breaker or fuse. Average power will be a couple watts which is the way the others are specified.
    Also, the Furuno FA50 is the only Class B AIS Transponder that does not use the same OEM Fixed Frequency RF Core that the other manufacturers purchase and it uniquely has a fully synthesized TX/RX transceiver!! I’ve tested this and it allows customers to easily create a completely private AIS Network on other VHF Channels besides AIS1 and AIS2. It has been used by customers who want to create a private Tender Tracking system or other privacy needs such as Private Buddy Tracking with Friends during tournaments. This capability was originally required by the USCG because of the U.S. AIS Channel legal issues with Maritel. Interestingly, because no other CLASS B can listen or transmit on any other frequency, it is impossible for others to track a FA50 in this mode. Any other “Private AIS” transmissions can be easily hacked because they all have to use the standard fixed frequencies. Of course, check with local authorities to confirm it is OK to place the FA50 into these secret modes.
    The FA50 also has a standard NMEA0183 I/O capability as well as a standard Ethernet 10/100 MBps IP Network Connection. This allows easy connections to Furuno Navnet Networks, PCs, and can even broadcast directly to the Internet for remote tracking anywhere on the planet.
    Furuno Tech

  23. Ben Ellison Ben Ellison says:

    Thanks, Furuno Tech; this is all interesting information, most of which I missed when I first bench tested the FA50 last winter:
    I’ve been waiting to further test it with the TimeZero version of MaxSea that I understood would ship with it eventually. But I don’t think that’s happened yet, right? However, I believe an MFD12 is headed my way for the radar testing, and I’ll certainly try the FA50 with it.

  24. I’ve been using the Simrad NAIS-300 class B transponder for about four months and am very happy with it. I do wish it had an onboard switch for disabling the transmit function, however this unit does have N2K (sold with N2K or Simnet, two choices available).

  25. Kees says:

    @Damon and David
    The NAIS-300 has exactly that capability as it is a TrueHeading / SRT in disguise — see section “2.7 Transmit Disable Switch” in the documentation.
    You do need to wire up your own switch, but that’s not very complicated. You can choose to have a “make/break” switch or a momentary push button.
    This has been discussed before, see Nauticast B mod, a “silent” mode switch.

  26. marinate says:

    “Also, the Furuno FA50 is the only Class B AIS Transponder that does not use the same OEM Fixed Frequency RF Core that the other manufacturers purchase and it uniquely has a fully synthesized TX/RX transceiver!!”
    Furuno Tech – I’m afraid you’re wrong here. All the other transponders also have fully synthesized transmitters and receivers and can operate anywhere in the marine band.
    “Interestingly, because no other CLASS B can listen or transmit on any other frequency, it is impossible for others to track a FA50 in this mode.”
    – all the other Class B’s on the market can be remotely commanded (by a competent authority) to operate on other channels.
    The ability to operate on other channels is required to increase the capacity of AIS when used in very busy areas and is entirely automated.
    Manually setting your AIS to operate on non-standard channels would kind of defeat the object, as no-one operating on the standard channels would see you…..

  27. Bob says:

    I think perhaps you forget the fishing for lobster, crabs, and to some extent salmon, halibut and plenty of other species is competitive. Why would a skipper knowingly add AIS where tracking services could show the highliner routes. AIS would need to be legislated before Ben’s vision becomes reality I’m afraid.

  28. Kees,
    We do have a remote switch hooked up to disable the transmit as per the installation instructions, what I meant by ‘onboard switch’ was that it would have been nice to have one already built into the unit rather than have to wire in a remote.
    I second all the mentions about having connectivity with a VHF that would allow easy calling to a specific target. Right now if I wanted to call a target using it’s MMSI number received on my Simrad transponder I would have to dial it in manually, not a very efficient way to spend my time if I’m trying to contact a ship quickly. It would be nice to select a target and hit a ‘call’ option so that the VHF would dial it automatically.
    Something else that would be nice is a remote display panel for the status LEDs. My Simrad like many other units are not designed to be surface mounted at a nav station for example because of the way the wires are connected. Many seem to be more cleanly installed in a place not visible, thus making the status LEDs less useful. If a transponder was to be mounted out of the way a very small remote panel with status lights would be nice for a quick glance to see what’s happening. Okay, how about a remote panel with a transmit disable switch incorporated with it!

  29. I wouldn’t think it would be too hard to bring the LEDs out to a panel using fiber cable. I don’t quite know yet how you’d terminate it at the panel, but I’m sure there is a way to do it.

  30. TimT says:

    All AIS transponders have to have a built-in GPS to ensure that the strict timing requirements of AIS are met, and this is why it is mandatory, so we won’t see the ability to plug in an external GPS.
    Regarding NMEA0183/2000, don’t forget that AIS started on commercial shipping, and their IEC data comms standard is effectively a superset of NMEA0183. Generally speaking, no commercial kit supports NMEA2000.
    FYI I’m just starting a test of AIS receivers and Class B transponders from a dozen manufacturers for Practical Boat Owner – should be in the December issue.
    Tim Thornton

  31. Ben Ellison Ben Ellison says:

    Thanks for posting, Tim.
    As I understand it, IEC 61162-2 is virtually a duplicate of NMEA 0183. But the new IEC 61162-3 does apparently add a new level of redundancy to NMEA 2000, and looks to be a powerful and foolproof data networking solution for large vessels.
    There’s some interesting detail about this, and the new V4 version of 0183, here:

  32. emsusa says:

    Add to the wish list, weather data from a vessel. It seems crazy that this is not part of AIS messaging, or at least an option. For search and rescue, knowing how hard the wind is blowing and from what direction would add to the situational awareness for responders. Imagine a tanker aground, wind plays a big part in where the oil goes.
    BTW, Ben, we have a lower cost 4x GPS antenna splitter we will be adding to our webstore soon. Let me know if you are interested in using one for your testing.

  33. Anonymous says:

    Tim T said, “All AIS transponders have to have a built-in GPS to ensure that the strict timing requirements of AIS are met, and this is why it is mandatory, so we won’t see the ability to plug in an external GPS.”
    Not to nit-pick, but it should be noted that the Class B internal GPS provides both timing AND positional data whereas Class A CAN use external GPS data for position. Class A internal GPS is primarily used for timing while providing backup for any external GPS.
    Bob Etter

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