NMEA 0813 and multiple units

[Big-Bang1]

Hi!
So, I currently have a chart plotter at the chart table that's attached to my ICOM VHF and a second chart plotter under the spray hood that's stand alone. I've just purchased an AIS Transceiver that outputs AIS targets to chart plotters via NMEA 0183 - Can I connect both chart plotters to my AIS whilst retaining the GPS output to my VHF?
All of the units are NMEA 0183 compatible.

 

[Andrew_Trayfoot]

It may work. If not something like this would help.
Digital Yacht MUX100 Dual Channel NMEA Multiplexer (MUX100)

 

[Andrew_Trayfoot]

NMEA/RS232 type date is designed to be 1 sender 1 receiver rather than 1 sender 2 receivers. But it may work...

 

[PaulRainbow]

Hi!
So, I currently have a chart plotter at the chart table that's attached to my ICOM VHF and a second chart plotter under the spray hood that's stand alone. I've just purchased an AIS Transceiver that outputs AIS targets to chart plotters via NMEA 0183 - Can I connect both chart plotters to my AIS whilst retaining the GPS output to my VHF?
All of the units are NMEA 0183 compatible.

No idea, you don't say what the plotters or the AIS are.

 

[laika]

NMEA/RS232 type date is designed to be 1 sender 1 receiver rather than 1 sender 2 receivers. But it may work...

I don't believe this to be correct. NMEA-0183 explicitly allows for one talker to talk to talk to multiple listeners with the maximum number of listeners constrained by the output of the talker and the input driver requirements of the listeners. I've seen various "Rules of Thumb" on this but it's never been less than 3 listeners which would cover the OP's case. As an installer, I'm sure PaulRainbow can give us his perspective.

Regarding the original question, per PaulRainbow's post it depends on the plotters and how you want to communicate with them.
Firstly the plotters need to support AIS over NMEA-0183 which as well as the ability to understand and display AIS input implies ability to communicate at 38400 baud. Either the plotter currently sending GPS to the radio needs 2 NMEA-0183 ports or the input and output speeds need to be settable independently because AIS input will be 38400, but the ICOM will expect its GPS at 4800. If there is only one input and one output but their speeds are independently settable, if you connect only the ouput (at 4800) to the radio, you lose the ability to receive DSC messages from the radio (most people seem not to care about this). If you connect only the input (at 38400) to the AIS, generally you don't lose anything except in special cases, e.g. my raymarine plotter can put my raymarine AIS into silent mode if and only if the plotter is connected to the AIS as a talker as well as a listener.

Of course if the plotters support AIS but only have one NMEA-0183 port each where the input and output speeds can't be set to different rates, you could always just use a cheap standalone GPS unit to feed the radio.

 

[PaulRainbow]

I don't believe this to be correct. NMEA-0183 explicitly allows for one talker to talk to talk to multiple listeners with the maximum number of listeners constrained by the output of the talker and the input driver requirements of the listeners. I've seen various "Rules of Thumb" on this but it's never been less than 3 listeners which would cover the OP's case. As an installer, I'm sure PaulRainbow can give us his perspective.

You're correct.

There may be a way for the OP to connect as he wants, but he'll need to tell us the makes/models of both plotters and the AIS. But if the plotters only have a single NMEA port it's common for the input and output to be operating at the same baud rate, which then won't all AIS in and GPS out. But then the AIS might have two output ports, one that can transmit at 38400 for AIS and another at 4800/9600 for GPS

 

[laika]

But then the AIS might have two output ports, one that can transmit at 38400 for AIS and another at 4800/9600 for GPS

Excellent point. My raymarine AIS 500 doesn't (officially) output GPS but does have a built in multiplexor which seems designed specifically for the case where a plotter has an existing nmea-0183 port connected to a VHF.