NMEA 2000 network Alert PGNs seem great, so why are they hardly used?

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.

13 Responses

  1. Ben Ellison Ben Ellison says:

    I don’t think that the pitifully low industry support for N2K Alerts is motivated by ill intent, or the result of simple lethargy. I suspect it’s more because even the ‘big’ marine electronics companies aren’t actually that big, and they all have lots on their development roadmaps. Plus there’s a negative network effect, as in “Why support brand agnostic Alerts if no one else is?”

    But maybe there are valid reasons not to support Alerts? Developers, please speak up.

    That said, the state of Alerts described by Paul seems damn sad to me. I know for a fact that a boat can be more reliable and easier to operate if any critical system can alert me about an abnormality or alarm me about a real problem. More to come.

    • Ben Ellison Ben Ellison says:

      The reason I’m so confident about the value of flexible N2K alerts and alarms is that I’ve had them on my boat for years thanks to various Maretron sensors and displays. For instance, I keep a temp sensor bolted to the main engine block set to a value slightly above normal operating conditions so I get warned about overheating way before the engine’s high coolant temperature alarm goes off. This is so important to my Volvo Penta — which has twice blown large exhaust manifold O rings and lost almost ALL coolant in minutes — that I have an alarm set up to activate very loud Maretron ALM100 alarm modules at both helms.

      And like DY’s nifty NavAlert, the Maretron DSM displays allow me to set up alerts or alarms on any value on the N2K network. However, Maretron designed this system before the standard NMEA 2000 Alert PGNs were published, so in many ways it’s a closed system, and sadly remains so. Checking recent manuals I see that Maretron alert PGNs are still all proprietary and thus won’t even pop up on a Garmin MFD.

      Moreover, if the standard Alert PGNs had already been widely adopted, the various Vesper AIS transponders I’ve tested over the years could have sent their valuable collision and anchor drag alarms to Gizmo’s ALM100s instead of me having to rig a less effective relay-driven audio alarm. In fact, I think there’d already be a lot more choices in alarm/alert organizers like the Maretron DSMs and NavAlert, and also loud N2K-powered sound alarms, if the MFD screens would do the right thing and spell out what the alert or alarm is about, and then offer to control it across the system.

      So I plan to search the PGN lists in the back of manuals for 126983 Alert, 126984 Alert Response, 126985 Alert Text, 126986 Alert Configuration, 126987 Alert Threshold, and 126988 Alert Value. And you can too. Maybe a list of who does and does not support Alerts would be motivating 😉

  2. Ben Ellison Ben Ellison says:

    Incidentally, I’ve known Paul Sumpner for many years and consider him a highly trusted source. That also means that I have an educated guess about the vessel using the unusual NavAlert alarms seen in Figure 2 above. I believe it’s the Sumpner family’s fascinating electric narrowboat Old Nick: https://thesumpnersafloat.com/

  3. Bob says:

    Definitely a chicken/egg situation. I was browsing the SignalK specs and their support for alert appears non-existent as well. Garmin can display them, but if nobody is sending them… I’ve noticed a similar dearth of support for the Anchor chain PGN’s which have also been around for quite some time. Again, Garmin can display them but nobody sends them.

  4. Bob says:

    derp. It looks like signalK does support alerts via the /vessels//notifications/ path.

  5. Paul Sumpner says:

    A Google search on “PGN 126983” returns a frustrating low number of products….

    1) Airmar with their latest SmartBoat product

    2) BM21 Lithium Cranking/Trolling battery… https://lithiumbatterysource.com/products/lithium-pros-12v-215ah-marine-starting-battery-with-nmea-2000

    3) Xantrex Freedom X Inverters… https://xantrex.com/products/inverters/freedomx/

    4) ComNav G series Satellite Compasses

    5) LXNav E Series MFDs

    6) JMA-3400 Series Radars

    • Ben Ellison Ben Ellison says:

      Yike. I think It’s great that Lithium Pros is trying to use NMEA 2000 well, but how will a user know that the promised battery alerts are not showing on their MFD (if it’s not a Garmin)? In fact, they footnote “The BM-21 embedded battery monitor… is “plug and play” with all NMEA 2000 multi-function displays” with this warning: “Check MFD’s documentation to insure it recognizes at least PGNs 127506 and 127508 for minimum compatibility.”

      However, while a user would likely see that 127506 DC Detailed Status and 127508 Battery Status were not showing in normal use, a 126983 Alert won’t go to their MFD unless something is going wrong. Lawsuits waiting to happen, and not really Lithium Pros’ fault?



  6. Ben Ellison Ben Ellison says:

    For a public list of all standard NMEA 2000 PGNs as of March 2023, download the PDF at the bottom of this web page: https://www.nmea.org/nmea-2000.html
    The list includes field descriptions like the PGN 126983 Alert fields you can see in the screenshot I used at the top of this entry.

    It’s my understanding that NMEA does not require manufacturers to transmit or receive any specific data PGNs, and that their certification process is mainly about validating proper network protocols. Like Paul, I can certainly see an exception for Alerts — and am tentatively glad that’s the case for OneNet — but I can also see that adding Alerts may be a significant burden for the developers.

    On the other hand, I’m pretty sure that NMEA 2000 certification does require manufacturers to clearly state which PGNs are transmitted and received, info that’s usually found in the back of the manual.

  7. Hi all three (including Paul),

    To add a comment, being a manufacturer, thank you for putting the spotlight on this under used feature!

    Garmin highlighted the same to us. And I was and still am convinced: super useful.

    Its on our list to implement, has been for quite a while, and we’re – slowly – getting closer to being able to work on it.

    R&D capacity is still our scarcest resource; in the midst of an abundance of pending ideas and improvements.

    Now, having learned from the article that only Garmin supports them, I might decide to move them a bit further down on the list ;o). (Thats a joke).

    Have a good day!

    • Ben Ellison Ben Ellison says:

      Thanks, Matthijs, you already improved my day!

      It’s excellent news that you have already recognized the potential value of these standard Alert PGNs. And as a manufacturer/developer who has already impressed a lot of vessel owner/operators — particularly those of us who appreciate good electric power monitoring and alerting — you could really help make Alert PGN support more widespread.

      For instance, if I could configure my Cerbo GX to output selected alarms to my boat’s N2K network, Furuno would hopefully become more motivated to support the Alert PGNs on their TZ series MFDs. Because then customers like me could get a clear notification like “Victron Cerbo: House Battery SoC below 20%” on the big screen we pay most attention to when underway. And of course the alert could be much more specific to a boat’s particular electric system and hence much less likier to ever be supported within brand by an MFD manufacturer.

      Moreover — if I understand the Alert PGNs correctly — Victron GX could also serve well as an Alert receiver. If, say, my N2K network included an N2K alert/alarm manager like Digital Yacht’s NavAlert, they could pop up on my GX Touch screen. Perhaps better yet, the alerts could get to me anywhere via my already rich VRM site ( https://vrm.victronenergy.com/installation/105905/share/ea38a0bd ). As Ben Stein just wrote in a side conversation: “…the remote aspect of those alerts would be a huge value add. Plus, potentially logging all those alerts and having a record…” Wow!

      Not that I’m pushing you to move Alerts up the Victron “pending ideas” list 😉

  8. Mike says:

    I wouldn’t be a bit surprise to find that some lawyer decided that implementing the alert but then having it fail to be delivered for some reason once it became relied upon would result in a huge lawsuit. There are instances of such “exposure prevention” risk management in other domains.

  9. Tom de Boerio says:

    Hi all !
    I am happy to report that our company has started using the NMEA Alert in new NMEA certified products. One of our product, the Interact DCM (https://www.sportsmanboatsmfg.com/seastar-interact-dcm-digital-switching-system) has supported it for a couple years to show faults such as low fluid level, open/short circuit, thank kind of things.
    It is a bummer that not more MFD support the system natively. Because of that, we support a simplified version of it (acknowledgement and fault history only) in our HTML page that can show on all big MFD brands.
    But it is definitively a round about way to do it !

    • Ben Ellison Ben Ellison says:

      Tom, I’m glad to hear that Dometic is adopting the N2K Alert standard, and thanks for reporting it here.
      I’m also glad to add more good news gleaned at METS:

      * Raymarine is purportedly adding full Alert PGN support to its MFD software.
      * Support for the standard Alert PGN’s is on Maretron’s “to do” (though they developed their own very capable alerting PGNs before the standard ones were created).
      * The emerging NMEA OneNet standard requires developers to support Alert PGNs whether they originate in OneNet or arrive via NMEA 2000 gateway.

      The going may be slow, but I’m optimistic for widespread Alert interoperability eventually.

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