NMEA2000 GPS data sharing

[Robin]

we have a Garmin plotter/GPS system with radar and AIS transponder all linked by NMEA2000 netwqork. The AIS black box came with it's own GPS Antenna mounted separately even though we have one for the plotter (same Garmin antenna in the ntwork). In the event of the plotter GPS antenna failing, would there still be positional data available to the plotter from the AIS one or is that totally exclusive to the AIS? I'm just thinking of backup and redundancy and if WE should consider another backup GPS< although we do run OpenCPN on a laptop, albeit mostly unreadable in sunlight outside.

 

[laika]

It depends. I think. I looked into this a lot for NMEA-0183 (as I don't have an N2K network). Same might apply to N2K but I couldn't swear to it. A lot of the last generation of popular AIS units were based on an SRT product which allowed the turning on and off of transmission of GPS via the proAIS configuration software (or sending a proprietary sentence by some other means).

My Raymarine AIS500 was based on one of those boards, but Raymarine borked it so that this was not an option. When I questioned them they claimed it was because they were sticking to the standard which required a "dedicated GPS unit". Hmmm.. Certainly you need a GPS dedicated input so you can input its position on your vessel but is that relevant for output??

So I think the answer is "maybe", depending on the unit you have...

Edit: Note that the AIS 500 also has a SeatalkNG interface: I just don't use it (and certainly the GPS output stuff is greyed out in proAIS). I believe Cardo has the newer AIS 650 and I *think* he said it will output GPS (but can't be sure...)

 

[Martin_J]

As Laika says - It is dependent on your AIS transponder. On the ones I have looked at, configuration has been possible and it has been possible to turn on (or off) the inclusion of GPS position sentences within the AIS stream.

I seem to think the default settings on these units was to include the position information. It was possible to turn off the inclusion so you didn't get two sources on one network.

As to the reason the GPS receiver is included as part of the transponder - I thought it was so that your position was accurately reported. Think how easy it would be to 'modify' your position if the transponder took your position from an incoming NMEA stream!

 

[Robin]

LOoks like I might need to buy me a basic handheld unit as a backup, although I have an APP on my smartphone that displays a lat :long, data that could be plotted on paper if I can find where I put the pencil.

 

[Martin_J]

Sounds like a plan assuming you use the plotter to make the conversion from the existing GPS antenna to the laptop for OpenCPN.

If the plotter is used for this conversion, then even having position information in the stream from the AIS transponder wouldn't help if your plotter failed.

If you have something else doing the conversion from NMEA2000 to the laptop then you might still find the position information on the NMEA2000 bus (from the AIS Transponder).

 

[Robin]

Sounds like a plan assuming you use the plotter to make the conversion from the existing GPS antenna to the laptop for OpenCPN.

If the plotter is used for this conversion, then even having position information in the stream from the AIS transponder wouldn't help if your plotter failed.

If you have something else doing the conversion from NMEA2000 to the laptop then you might still find the position information on the NMEA2000 bus (from the AIS Transponder).

Nope the laptop/OpenCPN has a separate BU353 USB puck GPS, perfectly useable below at the chart table but not visible outside in Florida sunlight.

 

[laika]

Nope the laptop/OpenCPN has a separate BU353 USB puck GPS, perfectly useable below at the chart table but not visible outside in Florida sunlight.

Maybe then one of those actisense N2K to NMEA-0183/USB jobs? Plug it into your N2K bus, plug it into the laptop. Presto: AIS and all your other nav data on the laptop. Then ensuring the "output on this port" checkbox is ticked on the actisense's data connection in opencpn options you can output the GPS from the BU353 onto the N2K bus which could be picked up by your plotter. Don't forget to set relative priorities of the puck and actisense thingy data connections to avoid any funny artefacts from two slightly different GPS inputs to opencpn.

If it's anything like my raymarine C90W there's may be some fiddling with the plotter settings to get it to accept an external GPS feed but the actisense NGW-1 I think is supposed to be bi-directional. Well, that's the theory: I'm all talk here: no experience of this device, only read about it.

Downside you need to run the laptop as well as the plotter. Plus the expense of the extra device.
Upside you get AIS and all your other nav data (including backup GPS from the plotter) on the laptop as a bonus.

 

[Buck Turgidson]

Does your VHF have GPS?
If your smart phone has a GPS chip why not get a chart app rather than another device?

 

[Robin]

Maybe then one of those actisense N2K to NMEA-0183/USB jobs? Plug it into your N2K bus, plug it into the laptop. Presto: AIS and all your other nav data on the laptop. Then ensuring the "output on this port" checkbox is ticked on the actisense's data connection in opencpn options you can output the GPS from the BU353 onto the N2K bus which could be picked up by your plotter. Don't forget to set relative priorities of the puck and actisense thingy data connections to avoid any funny artefacts from two slightly different GPS inputs to opencpn.

If it's anything like my raymarine C90W there's may be some fiddling with the plotter settings to get it to accept an external GPS feed but the actisense NGW-1 I think is supposed to be bi-directional. Well, that's the theory: I'm all talk here: no experience of this device, only read about it.

Downside you need to run the laptop as well as the plotter. Plus the expense of the extra device.
Upside you get AIS and all your other nav data (including backup GPS from the plotter) on the laptop as a bonus.

Bit complicated for a dumbo like me so probably a simple small standalone plotter isa good idea. There is a Standard horizon 5 inch one with built in antenna and full preloaded USA/ Bahamas/Canada coastal charts selling here for $320 which would be an easy install, even to the second (engine) battery bank as a double redundancy safeguard. THe existing plotter display et al is mounted in a coachroof mounted navpod and not easy access to connect other stuff to in a hurry. My original question was re the AIS's GPS antenna which is already connected to the NMEA 2000 network via the AIS 600 transceiver, which gives data of received ships AIS transmissions to the plotter but as this is only allowed it seems to give data to that, it is only for transmitting our position and cannot act as a backup to the primary GPS antenna which is exactly the same unit. Nuts or what? I guess the reverse is also true that the plotter GPS cannot act as a backup for the AIS transmission one either

Confusing? You bet!

 

[Robin]

Does your VHF have GPS?
If your smart phone has a GPS chip why not get a chart app rather than another device?

My smartphone is totally unreadable in sunlight but I guess I could put a black hood over my head!

 

[laika]

Bit complicated for a dumbo

No I just explained it poorly, sorry. The concept is you buy a $200 device which converts two way between your N2K bus and NMEA which OpenCPN on your PC understands. The idea is that that allows you to see your boat data on the laptop and also share the GPS attached to your laptop with everything else on N2K (hopefully including the plotter). That might be cheaper than buying an N2K GPS and gives you the added benefit of getting interesting stuff onto OpenCPN.

Unfortunately I just checked which information the version of that device with a USB interface converts and it seems not to convert AIS data. There's an AIS version which ends in bare wires which would need a bit more effort to wire into the PC so is a less satisfactory solution. I thought both versions did the same conversions but the AIS one was preconfigured for a higher baud rate but maybe I'm wrong. Anyone got an NGW-1 who knows the definitive answer?

 

[Robin]

No I just explained it poorly, sorry. The concept is you buy a $200 device which converts two way between your N2K bus and NMEA which OpenCPN on your PC understands. The idea is that that allows you to see your boat data on the laptop and also share the GPS attached to your laptop with everything else on N2K (hopefully including the plotter). That might be cheaper than buying an N2K GPS and gives you the added benefit of getting interesting stuff onto OpenCPN.

Unfortunately I just checked which information the version of that device with a USB interface converts and it seems not to convert AIS data. There's an AIS version which ends in bare wires which would need a bit more effort to wire into the PC so is a less satisfactory solution. I thought both versions did the same conversions but the AIS one was preconfigured for a higher baud rate but maybe I'm wrong. Anyone got an NGW-1 who knows the definitive answer?

I'm not bothered about losing the AIS display, only in having a working plotter showing our position on a chart if the main Garmin GPS fails since it seems the second Garmin GPS already on the N2K network via the Garmin AIS600 transceiver apparently will not jump in and take over the role of position finder in chief.

 

[Playtime]

we have a Garmin plotter/GPS system with radar and AIS transponder all linked by NMEA2000 netwqork. The AIS black box came with it's own GPS Antenna mounted separately even though we have one for the plotter (same Garmin antenna in the ntwork). In the event of the plotter GPS antenna failing, would there still be positional data available to the plotter from the AIS one or is that totally exclusive to the AIS? I'm just thinking of backup and redundancy and if WE should consider another backup GPS< although we do run OpenCPN on a laptop, albeit mostly unreadable in sunlight outside.

It depends on the plotter. What model is it and does it allow input/display of other NMEA2000 data in addition to the AIS data? If it does then what you are asking should work. However, the fault you are trying to cover is probably pretty rare (internal GPS failing but plotter and remaining electronics still working).

Most NMEA2000 multi function displays (clever plotters) have the ability to 'choose' their data sources and the Garmin should be no exception. Somewhere in the menu system for the plotter you should find a 'Network' (or equivalent) function. If you explore this you should find a sub-menu where you can choose the sources for the various data that the device can display. One of the sources should be position info (GPS data) and you should have the choice of internal or the data stream from the AIS.

Have a good look around in the plotter menu system and see. Alternatively tell us the plotter model and we'll see if the manual is available online.

 

[zambant]

I have a NMEA2000 network and you raise an interesting question - went down the boat today and turned off the GPS to the plotter - pulled it out and still getting gps data - must be from the AIS.
So looks like my system was getting gps data from 2 sources ........
Interesting - never occurred to me before
Hope this helps

 

[Robin]

I have a NMEA2000 network and you raise an interesting question - went down the boat today and turned off the GPS to the plotter - pulled it out and still getting gps data - must be from the AIS.
So looks like my system was getting gps data from 2 sources ........
Interesting - never occurred to me before
Hope this helps

Wonderful!, because we will have built in redundancy without trying if that is true of ours also. Is yours a Garmin system or a hybrid? Many thanks.

 

[Robin]

Update

I just spoke with Garmin Support in the USA who explained that the AIS keeps it's GPS data strictly to itself so if the main (and identical) Garmin GPS in the full Garmin N2K network fails the plotter display will not get positional information from the Garmin GPS that is connected to the Garmin AIS 600 transceiver, even though the AIS is supplying information on other AIS target vessels to the chart plotter and our position would still be transmitted . So at least I know, but it does seem a missed opportunity to have that redundancy built in. We do have a second plotter available in the form of a laptop running OpenCPN and fed by a separate Globalsat BU353 and can always use that at the chart table below, but it is unreadable in sunlight out in the cockpit. Navigating the ICW where we live is easier with a cockpit plotter display viewable from the helm and paper plotting whilst feasible entails much tiresome bobbing up and down twixt helm and chart table, not a problem when out at sea properly. I think therefore that I will keep a close eye on the bargain basement sales and/or secondhand market to find a simple standalone plotter with inbuilt GPS and pre-loaded USA charts, I have seen some fixed types at around $300 or even less for handhelds, one of which could do useful double duty in the tender.

I can feel the flames already about not relying on electronics and I am very capable of navigating traditionally as is SWMBO but life is too short and it is too hot/humid here to go stoneage unless we really have too and I sold the sextant anyway :nonchalance:

 

[Playtime]

. . . . the AIS keeps it's GPS data strictly to itself so if the main (and identical) Garmin GPS in the full Garmin N2K network fails the plotter display will not get positional information from the Garmin GPS that is connected to the Garmin AIS 600 transceiver . . . .

I've just taken a quick look at the AIS600 spec and noted that GPS data IS output in NMEA0183 format. It uses the RMC sentence (as well as VDM and VDO for the AIS data - see Page 9). This means that you could receive the AIS GPS data at the chartplotter if you can connect to it using NMEA0183.

I'm surprised the Garmin Support man didn't explain this. Maybe you were only talking about NMEA2000 connection?

 

[Robin]

I've just taken a quick look at the AIS600 spec and noted that GPS data IS output in NMEA0183 format. It uses the RMC sentence (as well as VDM and VDO for the AIS data - see Page 9). This means that you could receive the AIS GPS data at the chartplotter if you can connect to it using NMEA0183.

I'm surprised the Garmin Support man didn't explain this. Maybe you were only talking about NMEA2000 connection?

Thanks so more investigation neeeded. we have position data fed to our Standard Horizon DSC VHF which has to be in NMEA183 format so I need to ask our 'expert' installer where he took it from, the plotter display or the AIS black box just maybe. We have a raymarine autopilot too that AFIK is fed with NMEA 183 position data for the 'track' function to work although as yet I've not tested that and our 'expert' is occasionally economical with the real facts we have found.

 

[Playtime]

we have position data fed to our Standard Horizon DSC VHF which has to be in NMEA183 format so I need to ask our 'expert' installer where he took it from, the plotter display or the AIS black box just maybe.

I also have a Standard Horizon DSC VHF and feed GPS data to it (NMEA0183) from my AIS (Digital Yacht AIT2000). I'm prepared to bet a dollar that your GPS feed also comes from the AIS (assuming it is mounted below deck near the VHF)!

If this is the case then the only remaining question is "will the plotter accept the NMEA0183 RMC sentence" . If it does, you just need the NMEA0183 wiring installing and you're done.

 

[laika]

I'm surprised the Garmin Support man didn't explain this.

Not addressing Robin's Garmin problem but on the topic of questionable info from support on GPS output from AIS units...

After Raymarine UK had emphatically denied that the AIS500 can output GPS, I see there's a thread on the Raymarine US support site saying the exact opposite:
http://raymarine.ning.com/forum/topics/ais500-nema-output
Different firmware in the US? Can't see why there would be. Seems to be a list of SRT proprietary commands here:http://yachtelectronics.blogspot.co.uk/2011/02/srt-proprietary-ais-commands.html. I think some experimentation is in order...