AIS on ships, words from the gCaptain


Given some controversy about how big ships actually use AIS and what that may mean in terms of Class B, I asked Captain John Konrad to help out. Boy, did he, first querying his gCaptain readers, then bringing in Captain Richard Rodriguez for a professional small boat point of view, and finally e-mailing me with all the interesting comments below. This is the longest Panbo entry ever (and some of the best stuff is at the end). So how about a big round of applause for John, who somehow pulls all this off while still shipping out (he’s Chief Mate aboard a 835’ ship in the Gulf of Mxico right now, editing gCaptain by satellite!)

Captain John Konrad:

Clutter: Currently my ship has AIS overlay on the 3cm radar but it’s more of an afterthought. My previous two ships both had Furuno AIS-100 units with MKDs (Minimum Keyboard Displays). These units are very good in areas of little traffic but once we get over a dozen ships within VHF range there level of effectiveness diminishes. No matter how cluttered the traffic is, however, they are still useful since you can sort ships by name and CPA. Sorting by name helps you keep an eye on ships you already sighted while sorting by CPA (the mode I normally leave the unit in) helps you identify unseen dangerous targets.
   To answer your main question… boat targets will undoubtedly be subject to some level of filtering (whether electronic or mental) while in inland waters, but will not be filtered by ship officers while in open waters. I think this benefit alone overrides any concerns with the system. Also , while in inland water, we use visual means of avoiding traffic more heavily than electronic means. The opposite is true for a ship at sea.

How we filter data: Having radar overlay has a few benefits beyond the obvious. First it allows for better access and monitoring of “extra” data… my favorite being the rate of turn indicators (they look like the weather vane on a NOAA chart). Once I contact a ship via radio and agree on passing arrangements, I want to verify that she is actually taking the agreed upon steps. I am also interested in both her COG changes (how much my CPA is opening) AND her heading (from her gyro input). This assures me she is taking positive and appropriate action.

Communication: My favorite feature of AIS is the display of the ship’s name and MMSI number. Now, when initially calling a nearby ship, instead of making a VHF call”hailing the vessel in position L/L with a speed of x and course of y.” I can call the vessel by name. This has doubled the percentage of call backs I get in return. If the ship still doesn’t answer my call I can take the MMSI#, input it in my DSC controller and set alarms off in the other ship’s bridge (I also can change his working channel).

Extra info: Another little used feature I like is the antenna offset (this gets transmitted in the data stream as well). Simply add the bow-antenna and antenna-stern numbers and you have her LOA… great for giving you a feel at night for what you’re up against. Another great thing about AIS is data verification. The AIS data on a radar overlay system does exactly that, overlay on the radar target. If it doesn’t match up then you know you have a problem.
   Plus it adds redundancy. A few months back both our radars failed due to a technician’s mistake. This would normally leave us with only one means of determining CPA: lines of sight (steady bearing, decreasing range). Instead of putting our hands up we pulled out the radar transfer plotting sheets and transferred each target’s range and bearing from the MKD on 6 minute intervals. We thus found all the data we needed. Finally, the AIS update rate—again with the rate of turns—is faster than ARPA’s, which takes time to initially acquire a target and for the same reason has a delay in processing course and speed changes.

AIS A vs B data differences based on NavCen info:

* Has a reporting rate less than a Class A (e.g. every 30 sec. when under 14 knots, as opposed to every 10 sec. for Class A):
   I believe this is a problem with bandwidth. The maritime industry  pressed for quick implementation after 9/11 which meant they had to use existing technology. They chose to send the data transmissions via VHF, which results in ships competing for air time. I would really like to see future models have a WIMAX/cell/other based primary data output with the VHF channels providing redundancy.

* Does not transmit the vessel’s IMO number or call sign.
   Both are useless to boaters… the big question now is: does it display an MMSI #??

* Does not transmit ETA or destination:
   These are rarely updated by mates aboard ship anyway.

* Does not transmit navigational status:
   Not terribly important. I also never trust this data.. or any AIS data that has to be manually changed regularly. Hopefully once Integrated Bridge Systems develop AIS messages will be automatically updated by the system when nav lights are changed.

* Is only required to receive, not transmit, text safety messages:
   I don’t see this as a major limitation.

* Is only required to receive, not transmit, application identifiers (binary messages):
   Not sure what this means.

* Does not transmit rate of turn information:
   This is an important point! Also, will these receivers be tied to any heading indicators? What percentage of boats have anything but magnetic compasses?

* Does not transmit maximum present static draught:
   Not important.

My answers to Fred Pot’s concerns:

* Will commercial ships “see” me with an…AIS Receiver: No
   This is correct.

* …with a Class “A” transponder: Maybe. Few commercial ships display AIS targets on their radar.
This is false. I’d say while most ships don’t have radar overlay I know *many* that do. I also always set up my AIS to give CPA alarms (only offshore though, in inland waters I turn it off). If we do see you visually then we are going to check the AIS. If you have one we will have a better understanding of what you are and act accordingly… you will be safer. If you aren’t transmitting AIS info we will be uncertain whether you are a ship with a faulty/disabled unit or a small boat. IF you aren’t showing up well on radar then this information can be critical in helping us determine your COG, SOG and BCR.
   That being said, if I had my choice between seeing you on my radar or seeing your AIS info overlaid on my radar… I’d choose the former. SO INVEST IN A GOOD RADAR REFLECTOR FIRST! The more information we have about you (especially location but also p.o.b., name and size), the better we’ll be able to relay distress messages to the USCG. Also it will be easier to find you if you have an older EPIRB without GPS capabilities. We may not “see” you but we will hear you if we have our CPA alarm properly set. If you ever go missing at sea we’re more likely to remember that you, say, crossed our track last night… if we saw your name on our AIS display.

* With a Class “B” transponder: Probably Not. To reduce screen clutter Class “B” targets will be filtered from radar.
   Our survey disproves this theory but I can’t answer this question until I’m put in the situation described.

* Range is only about 8 NM (2 Watts versus 12.5 Watts for Class “A”).
   In my opinion this is a good thing (well except for ocean sailors). I also encourage all your readers to use the 1watt feature when calling nearby vessels… I always do. This limits communication to only the ships in the vicinity… i.e. only the ships you really care about. The caveat is that by limiting the range of the AIS we are less likely to see you in event of distress.

* GPS Position updated every 30 sec. (every 2–10 sec for Class “A”). 
   This is true and is not a good thing in my opinion.

* Messages only sent if the channel is free from Class “A” Messages.
   Not sure about this one. {It’s true, but the system has room for lots of messages—B.E.}

• Class “A” cannot understand Class “B” Identification Messages.
Not critical…. except for the all important MMSI number.

So my short answer is….

I welcome this technology and, while the claims regarding clutter are valid, electronic navigation is not our primary means of avoiding traffic in busy inland waters. At sea (or with less than 12 targets on the screen). I think professional mariners agree this will make everyone safer, especially those boats with a small radar footprint sailing offshore.

Ships do care very much about boaters they just *sometimes* don’t care to notice them in crowded waters because they have too much else on their minds and (as you said) have few options for maneuvering. In fact, when nearing a small boat with erratic behavior bridge teams are at their most attentive! In open waters small boat traffic is an important concern of all responsible mates.­­­

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.

8 Responses

  1. Pascal Goncalves says:

    Congratulation and many thanks… excellent and very useful thinking/opinion…
    From a sailor which believes in AIS very much.
    Pascal Goncalves

  2. DefJef says:

    What a post! Fabulous report on AIS.

  3. Ben Ellison Ben Ellison says:

    And some words from Steve Dashew:
    Hi Ben:
    Noticed the interview with the heavy metal driver re AIS. I’d like to add that this past spring using a Furuno AIS 150 on Wind Horse (83 footer), we had three situations where big ships contacted us based on our AIS output, to arrange passing information. In all cases they were the burdened vessel and we were going port to port. In 300,000 miles of cruising this is a first.
    Regarding effective range, we often pick up AIS targets at 25 to 35 miles, and on occasion have seen them displayed at 50 to 60 miles (ducting?).
    Finally, if you have ever been watching a ship on radar and then see it disappear in a rain squall, you will understand how valuable this is to a yacht – which is often invisible in just moderate sea-clutter.
    If I had to make a decision between investing in a life raft or AIS, I think I’d go with AIS.
    Regards – Steve Dashew

  4. George says:

    Great post, and a worthy example of how we have so much more information now.
    Regarding the false sense of security claim about class B — perhaps every unit should be sold with a brochure explaining that crossing in front of a big ship is like crossing in front of a train. Nobody (well, almost nobody) expects that the train is going to stop for them, which is why we are all taught to look both ways before crossing tracks. It does not matter how well the train crew can see us. This goes for radar reflectors and VHF as well. I hear far too many sailboats calling up big ships (on 16!) to complain about right of way.
    As far as clutter, technology will take care of that. The neat thing about AIS is that you have a definite target location. MARPA relies on sophisticated algorithmic guesswork which is subject to a large degree of error in common situations. With the precision of AIS we will be able to come up with far more accurate (but not perfect) collision avoidance algorithims.
    Finally, I think the biggest advantage of Class B is for yacht-to-yacht interactions. Take one example. If it were common for the bigger yachts, it would make navigating rapids up here in the NW much easier. It would be nice to know if there were a bunch of boats “around the corner” waiting to cross. We will never get rid of securite announcements, but this will certainly be a help. Being able to push a button to activate the other yacht’s VHF is a big advantage that I had not thought of until reading this blog.

  5. John Foster says:

    From the Macsailing site:
    “…SNIP…Lloyds Maritime Information web site. Amongst various interesting marine data sources they provide is an AIS network, covering what looks like hundreds of ports world wide.
    Of particular interest is the AIS Free service that they provide, with provides data for the major ports. I’ve registered for this service and as soon as I get more information, will update you.

  6. Milt Baker says:

    Every yachting skipper I know who uses AIS seems to appreciate having other ships’ names displayed. Even the sleepiest watch officer comes awake when his ship’s name is called on the VHF! As far as I’m concerned, that alone justifies the cost of an AIS receive-only system for those who venture more than a few miles offshore.
    After using a receive-only AIS system for a trip from the Eastern Seaboard to Venezuela and return to Maine via Bermuda, I added a two-way system and have been most pleased with the Furuno AI-150 we now have aboard Bluewater. Two-way AIS is one terrific tool.
    But using AIS intelligently is the other half of the equation. As far as I’m concerned, it pays to resolve ambiguous crossing situations early and positively. When it appears that we’ll pass within two miles of another vessel well offshore, our SOP is to “negotiate” the pass while there’s still plenty of time.
    If we’re the burdened vessel, I will normally call the other vessel and announce my plans, as in “Our intentions are to change course 20 degrees to port to give you a safe pass of 2.7 miles.” If we are the privileged vessel and the pass will be two miles or closer, I find it useful ask the other ship to alter course and to be specific about telling him what I’d like, as in “We request that you alter course 20 degrees to port to give us a safe pass of 2.0 miles or greater.”
    Using proper radio-telephone procedure and coming across professionally seems to pay dividends. In many such conversations, we’ve had only one ship refuse our request.
    In the hands of an experienced, attentive watch keeper AIS is a real life saver! Without someone who knows how to use it, it’s just another piece of fluff.
    –Milt Baker, Nordhavn 47 Bluewater

  7. Fred Pot says:

    US Flagged Commercial ships generally have well trained officers and quite sophisticated navigation equipement, as Capt. Konrad explains.
    As boaters we need to worry also about the majority of ships’s officers are less well trained and have no way to display AIS targets on their radar.

  8. gulfcoast says:

    Looking for help in finding marine electronic manufacturer’s in Brazil who desire to present an AIS product to the market under their own brand or through their sales channels. We provide solutions in two formats: a complete OEM product, or a PCA module.
    Thank you in advance.

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