GPS rollover and raymarine GPS receivers

[phorvati]

So I have a RS125, C120 MFD along with S3 course computer and ST8002 Controller.
RS125 GPS on Seatalk is showing 2003 for a date due to 1024 week rollover.

I have two other NMEA183 GPS receivers and EM-track B-100 AIS transponder that has its own GPS and talks to C120 via NMEA183 but at 38,400 baud rate.
It seems that once I removed RS125 from seatalk, MFD ends up getting a fix from AIS. But its not sending GPS data to Seatalk nor does it display the GPS satellite signal information, but date is correct. It would be nice to have GPS on seatalk as I have repeaters, and a spare C70 MFD down below.

Sifting through manuals, looks like S3 or ST8002 have NMEA183 port and appear to be able to decode GPS data. Manual specifically list which sentences get extracted by S3 or ST8002.
Has anyone tried this and does that mean if I connect one of my spare GPS receivers to this NMEA183 port, I can get GPS data back onto Seatalk that way. Becasue Raymarine suggestion is RS130, or RS150 and then Seatalkng to seatalk converter to the tune of 300$-500$. And RS130 glitches in 2027 while RS150 glitches in 2033.

[smac999]

The auto pilot cpu will probably convert nmea 183 data to the seatalk bus. But it will probably only take 4800baud.

[HeywoodJ]

What happens if you turn off the AIS? Do the other GPS sources fill in and pass information to Seatalk? I’m wondering if position information from the AIS is coming from the VDO sentence?

We have Raymarine gear that passes position information to Seatalk, but the position information comes in as RMC (IIRC GGA also works).

[phorvati]

Don't want to mess with turning off AIS.


I have digital Yacht 150 that sends data to a PC running OpenCPN.

I will re-route that to ST8002 NMEA port.
OpenCPN is already getting same AIS/GPS data as C120 via NMEA183 and it can probably parse all the AIS data.

My third GPS is connected to PC for Position reports via Airmail.



As far as 4800 im ok with that. I will test and see what happens.

My only question is, will I have GPS satellite info and correct date so that tides are correctly displayed on both MFDs. Im hoping to have the same functionality as if RS125 was connected.

[SailingHarmonie]

Originally Posted by phorvati

So I have a RS125, C120 MFD along with S3 course computer and ST8002 Controller.
RS125 GPS on Seatalk is showing 2003 for a date due to 1024 week rollover.

The last GPS epoch rollover happened in April 2019. You have had this problem for 4 years? I don’t remember Raymarine being significantly affected by it.

[sailingharry]

There is a difference between the official rollover and the practical rollover. I have two Furuno GPS systems and they both rolled over at different dates in early 2022. My assumption is they did something like an algorithm that uses a different start point. In other words, weeks 200 through 1024 are calculated normally, but weeks one through 200 are assumed to be in the next epoch. Kind of like telling somebody you were born in 61, nobody assumes you meant 2061.
The date appears to be the only symptom of a GPS incompatible with rollover (time and all positional information remains accurate). This actually makes it very difficult to notice, as the only date information most of us use on a chartplotter is tied data -- and depending upon your use that may not be used often. On my plotter, I was able to set the time (and date) data source to be the AIS receiver.