NMEA 2000 article (a cautionary tale)

[TwoFootitis]

I was researching how to connect a hummingbird fish finder, Cannon down riggers and my R23 Garmin equipment over the NMEA 2000 network and came across an article that's worth sharing.

https://www.morganscloud.com/2013/05/26 ... e-obvious/

All about redundancy and safe boating!

Enjoy!

 

[CaspersCruiser]

That is a sobering thought, although I’ve not heard that NEMA 2000 backbone failure is a common problem. I do carry two iPad Pro 12.9” tablets with a Dual 160 Bluetooth GPS. I have Aqua Maps, Navionics, SEAiq, and TZiq navigation apps. I do not carry paper charts.

 

[S. Todd]

After decades of navigating the Great Lakes with just a compass and paper charts, I am comfortable with that as my backup.

 

[FlyMeAway]

Also, remember that at least since the 74xx series, most (all?) Garmin plotters come with an integral, backup GPS/GLONASS antenna -- this was not true in 2012, when the article was published. My understanding is that this was designed as a safety feature against NMEA200 backbone failure -- and simplify installation, but primarily as a safety feature.

I haven't checked how things are wired on our boats, but I've also been told by a marine electronics installer that best practice is to wire the VHF via NMEA0183 instead of NMEA2K so that backbone failure doesn't interfere with the ability to send out a DSC distress call (I was speccing a complete electronics overhaul on a sailboat). But it is also a good reason to have a DSC-and-GPS-equipped VHF handheld (both ICOM and Standard Horizon make them) on board as backup.

 

[FlyMeAway]

Also, one thing that is great is having an AIS with an integrated WiFi NMEA repeater (the Vesper Cortex has this). If the plotter fails, you can still overlay AIS on a third-party charting app on your phone or tablet (or you can get mapfree AIS with Vesper's app) and you get another GPS source (because AIS requires its own non-networked antenna, again for safety reasons). Yet more redundancy.

 

[BB marine]

Interesting article. I can post my experience of a total N2K failure on my C26 Cutwater. What happened? The Chart plotter worked and gave position and chart was available. It has a built in GPS antenna. This was the 7612 XSV. What did not work, auto pilot would not turn on, the Volvo information would not talk to the Garmin, the fusion radio would not function ,Vhf AIS would not function properly No GPS signal. The external GPS would not work but the internal did so really no navigation issues except AIS and VHF distress. I use a iPad with Navionics as my redundant navigation chart plotter. So my experience was not as bad as the article States but still not a good situation.

What happened? I noticed that the Fusion radio no longer talked to the Garmin plotter. The fusion radio also began to freeze up. Then I noticed my Volvo information was not talking to the 7612 and my auto pilot would not work. I called Garmin and they gave me some checks and trouble shooting steps. They did tell me that the back bone connectors can fail and that the ends of the back bone need to have termination connected at both ends. There also must be voltage preset to the back bone for it to work. I took the back bone completely apart inspecting connections and looking for voltage. I purchased a new N2K T connector and used it as a troubleshooting devise looking to see if I had a bad connector. I could not detect voltage. Garmin said look for the yellow power cord and connector. No where to be found!! After removing the complete back bone and tracing each wire from the back bone to its source . ( This required removing all the interior components in the cave and a lot of descriptive words spoken!!!!) After tracing each cable I determined that the back bone power was coming from the NRX feature of the fusion radio. The fusion radio had been working erratically and required a reset. When the reset took place the NRX feature turned off and this shut the back bone down. I called Garmin and told them what I had found. They told me that the fusion NRX does not provide enough power to power the back bone and that is probably why the fusion radio was acting up. They advised to install a dedicated 12V source fused with a 3 amp fuse to power the back bone and remove the fusion NRX power supply. This was not an acceptable way of powering the back bone.

I called Fluid Motion and spoke to a representative and he confirmed this was the way they wired the backbone and they have had no issues. I explained that Garmin said this was not a correct install and that I did have an issue. So there are issues with this install. ( My fusion radio failed and I needed to replace it. Unfortunately it was out of warranty )

I don't know if Fluid Motion is still using this method but I doubt it. I hope that they are not. I do know that several 2015 and 2016 Rangers and Cutwaters were wired this way. I know this because I have talked to the owners and walked them though the troubleshooting steps. The quick and easy first step now that I KNOW THE ISSUE IS RESET the Fusion radio. Then go into Menu scroll down to NRX and turn it on. If all N2K functions are working that is your power supply. Now Turn the NRX off if the backbone function is gone ( no communication between the electronics) the back bone is powered by the fusion radio. I would advise changing this and adding a separate 3 amp power supply to the back bone.

We all have electronics onboard and have learned to navigate and trust them. This is expensive equipment and for the most part reliable. Proper installation is a key to reliability. We all know though , reliability is not always guaranteed so have a back up plan!!!

 

[Dcsqatar]

My 2020 R29S (delivered in July/2019) had N2K problems from the start, which took over a year to resolve. The main problem was the installation of the backbone itself, as documented in an early post which I have excerpted from below:

"the cause was determined to be poor connections between "T" branches in the NMEA backbone. The method of installation by Ranger was to assemble the "T"s together (8 in total) and then tie the assembled backbone down in the space forward of the cave on the starboard side. The assembled backbone was about 16 inches long and held in place by just two screws. The solution was to tie all 8 Ts in the assembled backbone to a piece of wood (each "T" has its own screw-down point) and then install the complete assembly. This avoids bending the backbone during installation and also (hopefully) the intermittent loss of connectivity while operating the boat."

I have had no issues since the improved backbone stability assembly was implemented. Regarding this article/post and N2K reliability, my experience was: (1) there is a dedicated power connection to the backbone as installed by the factory, (2) poor connectivity in (most likely) one connector on the backbone did not impact all devices but just those (VHF and AIS 800) on one end of the backbone. Basically they lost GPS input and AIS lost transmission via VHF antenna. Radio still worked (but no DSC) and AIS received but could not transmit. At least in my experience, backbone problems had limited impact on device functionality, most kept working without issues. Along the way, I added another GPS receiver dedicated to the AIS800, so no longer needs GPS from Chartplotter.

 

[Submariner]

Garmin said look for the yellow power cord and connector. No where to be found!! After removing the complete back bone and tracing each wire from the back bone to its source . ( This required removing all the interior components in the cave and a lot of descriptive words spoken!!!!) After tracing each cable I determined that the back bone power was coming from the NRX feature of the fusion radio.

They advised to install a dedicated 12V source fused with a 3 amp fuse to power the back bone and remove the fusion NRX power supply.

I don't know if Fluid Motion is still using this method but I doubt it. I hope that they are not.

The new boats coming from the factory today have the yellow N2k T which is powered off the DC fuse block.

Illustration of the yellow N2k T that provides power to the bus.
https://www.letsgochannelsurfing.com/autoglide?pgid=kxcmp6wc-27266dda-511d-426f-8ea7-744cc78b2694

 

[FlyMeAway]

(2) poor connectivity in (most likely) one connector on the backbone did not impact all devices but just those (VHF and AIS 800) on one end of the backbone. Basically they lost GPS input and AIS lost transmission via VHF antenna. Radio still worked (but no DSC) and AIS received but could not transmit. At least in my experience, backbone problems had limited impact on device functionality, most kept working without issues. Along the way, I added another GPS receiver dedicated to the AIS800, so no longer needs GPS from Chartplotter.

I'm surprised that nobody explained to you that this is definitely not an NMEA2000 issue 🙂

By design and by requirement, Class B AIS units like the AIS 800 cannot take a GPS reading off of NMEA (2K or 0183) and must have an independent GPS antenna that is not networked. This is precisely because an NMEA network failure would interfere with AIS transmit, which is a safety issue. The other networked devices can use GPS off of Class B AIS, but not the other way around. The GPS "receiver" you added to your AIS 800 is just an external antenna, not a complete receiver -- the receiver has to be integral to the unit.

The loss of AIS transmission was solely because your AIS lost GPS fix. My guess is that the AIS was somewhere belowdecks with poor GPS signal (before you added the external antenna). Loss of AIS transmit was unrelated to NMEA2K issues but instead based on poor reception by the internal antenna on your AIS unit.

On the other hand, your VHF needs to get GPS signals from *somewhere* to transmit them for DSC distress.* This is usually done via the NMEA2K backbone. However, as was explained to me a few years back when I was designing a complete electronics overhaul on my last boat (ended up selling before pulling the trigger on that one), for safety purposes the ideal configuration is to direct wire an NMEA0183 connection from the AIS to the VHF if they are separate units. You can still connect the VHF and the AIS to the NMEA2K backbone for other data, but sending it over NMEA0183 is the belt-and-suspenders approach recommended by the guy I paid to design the system.

Make sense now?

*FN: What I don't know in practice is how this would work in a rescue situation with VHF and AIS if your VHF loses GPS but AIS is still transmitting. Say your VHF isn't getting GPS signal. I have been given to understand (but to be clear am not sure) that DSC distress calls still works but do not transmit your coordinates (according to some friends at the USCG, they will then triangulate your position based on the distress call). But, if you have functioning AIS on the same MMSI, I would guess (but again, am not sure) that the USCG or other competent rescue authority would see your AIS transmit, match the MMSI to your distress call, and know your location.

 

[H28]

After decades of navigating the Great Lakes with just a compass and paper charts, I am comfortable with that as my backup.

Amen Brother...........

 

[SJI Sailor]

Quite apart from N2K, chartplotters can fail for other reasons. We have a current problem with our 7612s, where they stop drawing all land and contours on occasion -- showing only white background as if it were wide open water (!)

That could be dangerous if it went unnoticed and is somewhere between annoying and dangerous coming into a harbor, etc., even when it is noticed. (Rebooting fixes it. Need to call Garmin beyond that. FYI the firmware is up to date.)

Bottom line: carry some kind of backup to chartplotter and know how to use it. (We have paper charts + AquaMap.)

 

[Chimo]

After decades of navigating the Great Lakes with just a compass and paper charts, I am comfortable with that as my backup.

Amen Brother...........

I’ve always carried a handheld compass to take bearings. Mine is this one https://us.binnacle.com/p987/Davis-215- ... _info.html. I also have good binoculars with a built in bearing compass. I guess I could rely on my phone for both gps and/or compass but……..

 

[Dcsqatar]

FlyMeAway, thanks for adding to my continued education on NMEA 2K. Looking back at my post, I was both a bit unclear and also mistaken about AIS sourcing GPS off the backbone. My backbone problem did not impact GPS to AIS, but as I stated, it impacted access of the AIS to the VHF antenna rendering AIS position broadcasting inoperable. This problem (no AIS position broadcast) persisted after addition on the external AIS GPS antenna, and was therefore presumably a backbone problem as stabilization of the backbone resolved it. You are correct that AIS has its own GPS and does not get that data from any other device on the backbone (my bad!). According to Garmin, the vertical installation orientation of my AIS800 unit negatively impacted the GPS reception from its internal antenna, leading to the decision to install an external antenna.

 

[FlyMeAway]

FlyMeAway, thanks for adding to my continued education on NMEA 2K. Looking back at my post, I was both a bit unclear and also mistaken about AIS sourcing GPS off the backbone. My backbone problem did not impact GPS to AIS, but as I stated, it impacted access of the AIS to the VHF antenna rendering AIS position broadcasting inoperable. This problem (no AIS position broadcast) persisted after addition on the external AIS GPS antenna, and was therefore presumably a backbone problem as stabilization of the backbone resolved it. You are correct that AIS has its own GPS and does not get that data from any other device on the backbone (my bad!). According to Garmin, the vertical installation orientation of my AIS800 unit negatively impacted the GPS reception from its internal antenna, leading to the decision to install an external antenna.

No worries! NMEA2K is confusing. The safety issues you mention are also why best practice is to direct wire GPS to the VHF via NMEA0183 not NMEA2K

 

[TwoFootitis]

Great discussion, it was good to hear everyone experiences. Unfortunately, it didn't get me any closer to connecting a hummingbird fish finder, Cannon down rigger and the R23 Garmin equipment over the NMEA 2000 network.

😀

 

[CruisingElvinRay]

I’ve connected two additional items (two separate installations) to my NMEA 2000 network on my r-23. I each case, I ended up replacing the single T with a double T and then a quad T The Lenco Autoglide was first, then the Garmin GPS 24xd.

In both cases, I had to pull the autopilot display out to remove the screws holding the Ts in place. Everything else was relatively straightforward.


Sent from my iPhone using Tapatalk

 

[Submariner]

My boat came with the following connected to the N2k bus.
* Garmin Chartplotter
* Standard Horizon VHF Radio
* Yamaha Engine controls
* Fusion Radio
* GHC 20 (auto pilot display)
* Reactor (Autopilot)
* 12 volt power

I've added the following to my N2k bus:
* Lenco Autoguide
* Vesper XB-8000 AIS transponder
* Garmin GPS 24XD (GPS receiver)

I ran out of horizontal room behind the helm and had to pull out some single-T's and put in a multi-port T (4 port). The multi-port T (4 ports) takes up a lot less horizontal space. I just bought a second multi-port T to add as I've got one other item I'll be adding and I'm out of horizontal space (again). (Wind transducer).