NMEA 0183 Port Baud rate, AIS etc.

prologica

prologica

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Afternoon All,

I'm in a bit of a dilemma with an AIS set up - help appreciated please.

I have an older Raymarine C120 Classic MFD (plotter) with existing Seatalk connections and just one NMEA 0183 port. Currently this port outputs course data to a cockpit repeater at (I'm pretty sure) 4800 baud. The repeater also takes position data at same baud from a separate GPS.
Now I'm hooking up a McMurdo M15 AIS receiver to the plotter. This can be connected to the same NMEA 0183 port but the issue is the AIS should output at 38400 baud. If I set the plotter baud to 38400 it'll be happy with the AIS data but the one port will then send the position data at 38400 to the repeater which it can't handle.
The AIS unit has a built in multiplexer which can configure input and output at 4800/9600/38400 but not sure that helps as its the C120 plotter to repeater where the problem lies.

Any suggestions please?
Thanks
David
 
I'm in a slighty similar situation, albeit with a Lowrance plotter, Radio Ocean RO4800 AIS/VHF and Raymarine autopilot. Like yours, the plotter can accept multiple NMEA inputs, but only at a single baud rate.

There's no multiplexer, but the VHF will output AIS data at 4800 baud, albeit with a warning that function may be degraded compared to 38400. No harm trying, I thought, so I set it to 4800. The plotter happily accepts and displays the AIS data and tells the autopilot what to do. I suspect that if there's a lot of AIS data flying about, the system struggles to process all of it, but that's not generally a problem where I am.

P.S. A new plotter's on the list. Why is it that it keeps getting longer?
 
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I have the same problem with a Lowrance HDS Gen 3 plotter/sounder because it to cannot have different baud rates for nmea in and out. So my McMurdo AIS is to set to output at 4800 which works fine given the relatively traffic free West Coast of Scotland.
(The HDS needs to output 4800 for the AP otherwise I could have left the AIS at 38k.)
 
Thanks guys, I'm on the Thames Estuary so anticipate lots of targets. Like you I'm thinking of trying 4800 for AIS but would prefer a more robust solution. Anyone else got a solution?
 
It would probably be cheaper to replace the repeater for one which supports 38k baud unless one of the resident Arduino nerds :cool: can come up with a rate converter for you.
 
prologica said:
Anyone else got a solution?
Click to expand...

Assuming the information displayed by the cockpit repeater is available on Seatalk, how about a Seatalk -> NMEA converter instead of plugging it into the plotter? Or see whether any of your other Seatalk devices already have an NMEA output, there are some that do.

Pete
 
prologica said:
Thanks guys, I'm on the Thames Estuary so anticipate lots of targets. Like you I'm thinking of trying 4800 for AIS but would prefer a more robust solution. Anyone else got a solution?
Click to expand...

If the AIS data doesn't work well at 4800, your other choices are a Seatalk-NMEA0183 converter (as prv mentioned) or a rate-changing multiplexer which will take the plotter's course data at 38400 and output it at 4800 for your repeater.
 
Hi - I would be interested to know what you call a cockpit repeater - is this another Classic MFD or something else - does it have NMEA and SeaTalk ?
 
Hi Delfini,
The repeater is not an MFD it's a waypoint/bearing/x-track/speed repeater - a Clipper star I believe. Pretty sure it doesn't have Seatalk and only supports 4800.
 
prv said:
Assuming the information displayed by the cockpit repeater is available on Seatalk, how about a Seatalk -> NMEA converter instead of plugging it into the plotter? Or see whether any of your other Seatalk devices already have an NMEA output, there are some that do.

Pete
Click to expand...
Hi Pete, will the Seatalk connection from the c120 carry all data from the plotter data automatically or does that need to be configured in some way?
 
prologica said:
Hi Pete, will the Seatalk connection from the c120 carry all data from the plotter data automatically or does that need to be configured in some way?
Click to expand...

As far as I know you can't configure what gets put on the Seatalk bus. "All data" is rather vague, but the sort of basic information you describe in post #9 should be there automatically. A dedicated Seatalk -> NMEA bridge would almost certainly output the NMEA sentences you need. NMEA-equipped instruments like the ST60 Multi or an autopilot, if you have them, probably will too, but it would be worth checking first since their NMEA support is sometimes a bit deficient.

Pete
 
Hi David - I can see your repeater only has NMEA so that limits your options but I am not sure why you cant configure the NMEA port on the plotter to 38400 and connect to the AIS receiver and use the 4800 AIS mux output port to connect to the repeater ?
 
Delfini said:
Hi David - I can see your repeater only has NMEA so that limits your options but I am not sure why you cant configure the NMEA port on the plotter to 38400 and connect to the AIS receiver and use the 4800 AIS mux output port to connect to the repeater ?
Click to expand...

But the M15's only output port is the one which sends AIS data to the plotter at 38400 baud, isn't it?
 
I think that's right Delfini, whatever you input to the M15 AIS unit is output with the AIS data. The output baud can be configured but 38400 is preferable for AIS data.
 
Perennial problem with single port MFDs. Quickest route to sanity is a multiplexer eg Actisense or Brookhouse. Unfortunately not cheap solution but gives you future flexibility as well, depending on device.
Do you also feed position to VHF for DSC?
 
Does the AIS device not have N2K output ?. Then you could used that for AIS output to the HDS and keep the HDS to AP on NMEA0183 ?? That would then permit differing baud rates as the HDS can have different settings for nmea0183 and 2000
 
mparrish said:
Does the AIS device not have N2K output ?. Then you could used that for AIS output to the HDS and keep the HDS to AP on NMEA0183 ?? That would then permit differing baud rates as the HDS can have different settings for nmea0183 and 2000
Click to expand...
No, the McMurdo AIS doesn't have N2k.
I do have the option of using my Shipmodul 2usb multiplexer which can accept different baud rates on the inputs, as well as Seatalk on input 4, and has two outputs, one of which will drive the AP at 4800 and the other can operate at various baud rates.
It has sentence filtering and routing so it provides great flexibility, as well as a usb output for PC.
input 1, Pos + depth from the HDS
input 2, backup gps /spare
input 3 AIS + wind from the McMurdo
Input 4, Seatalk from AP (SPX30) for heading
Output 1 - AP data & pos to SPX30 at 4800
Output 2 to HDS for AIS, depth, wind, & HDG, and also to the nmea to wifi adaptor for the tablet. (I wished I'd bought the Shipmodul wifi multiplexer)
 
What a saga this has been...and still no AIS! In summary, during attempts to connect AIS, we lost radar data on the C120 Classic plotter, plotter was starting with a Miami chart and plotter kept freezing with soft keys inactive. Called in an engineer to sort us out - they reckoned the plotter needing to go to Raymarine for repair, and a new GPS antenna was needed to sort out the problem before they started on AIS. They also questioned certain wiring which raised doubts as this was clearly a pre-existing connection. On Good Friday I visited the boat myself, did a factory reset and hey presto, normal service was resolved!

Now, back to AIS: Our key issue is that a 4800 baud cockpit repeater is already connected to the plotter's single NMEA0183 port. I contacted Raymarine to ask if their AIS350 receiver with its built-in multiplexer would interface to the plotter without need for a further external multiplexer. I wasn't sure if it would be any different to the McMurdo M15 I'd already bought as that features an internal multiplexer too. What was interesting about their reply was the suggestion that the repeater should be connected to the output of the AIS unit i.e. the AIS unit sends AIS data at 38400 to the plotter and the plotter returns route data to the AIS unit also at 38400. The built in multiplexer converts this data to 4800 for the repeater to display. Eureka! I thought...the M15 with its multiplexer surely does the same? Interestingly though, whereas the Raymarine AIS has 8 data wires - positive and negative input and output pairs at 4800, ditto at 38400, the McMurdo unit only has 4 data wires - positive and negative input and output pairs, with the ability to configure input and output at different baud rates. So I think that means that the McMurdo could only be configured as Raymarine suggest for their unit, if the pair of input wires operated bi-directionally at 38400 sending AIS data to the plotter and receiving route data along the same pair, and the pair of output wires sent the route data at 4800 to the repeater. But surely the input wires cannot both send AND receive data?
 
Looks like you are having fun but I reckon your idea of a multiplexor isn't quite right - originally you said "the AIS unit has a built in multiplexer which can configure input and output at 4800/9600/38400" - further comment suggests the AIS unit merely provides single NMEA input and output port/s which can be set to different speeds - but that's not a multiplexor in my book. A proper mux (maybe like the AIS350 or better yet the Brookhouse iMux so you can keep your existing AIS unit) provides several NMEA ports (and if you are lucky a Seatalk port) and 38,400 AIS/plotter data presenting at the primary input to the mux also appears on other secondary NMEA port/s - maybe set to 4800 and connected to your repeater ?

Good luck
 
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