NMEA - sentence frequency / capacity

[MattS]

Hi,

I recently bought a Nasa Tactical Wind Instrument, which I chose over the standard Nasa Wind Instrument on the basis that it was only £20 more and it transmits NMEA sentences at 10Hz rather 1Hz. £20 seemed worth paying for a much more responsive instrument, but for the sailing I'll be doing it's not going to make a major difference.

My thinking was that although I don't have a NMEA 2k system at the moment, in the future I could use an NMEA 0183 -> 2k gateway to integrate this wind instrument into that system, rather than having to replace it all again.

Clearly the Nasa tactical wind display must be capable of receiving 10Hz updates, but I've just read something that suggests 10Hz NMEA 0183 sentences could easily flood the capacity for NMEA 0183 listeners at a 4800 baud rate. Does this mean I've essentially bought something that will practically never work as a feed into other instruments as it'll just be too chatty?

Is anyone expert enough in NMEA 0183 / 2k to tell me whether there's a way I would be able to integrate this instrument successfully into, for instance, a NMEA 2k via a gateway in the future?

 

[PaulRainbow]

Integrating 0183 into N2K will depend on what the system comprises of. You may need to install a converter or you may be able to input the 0183 data into certain devices that will multiplex the data and output it onto the N2K network. For instance, Emtrak AIS transponders have two 0183 inputs, the device will output the data onto the N2K network. Most (all ?) Garmin chart plotters have a single 0183 port, which will also output the data on N2K.

 

[ithet]

The main extra feature of the Tactical Wind is the ability to give true wind direction providing a suitable speed input was provided. I would think that was worth the £20? There are a number of ways to integrate with N2k so you will be able to do this.

 

[laika]

Does this mean I've essentially bought something that will practically never work as a feed into other instruments as it'll just be too chatty?

Is anyone expert enough in NMEA 0183 / 2k to tell me whether there's a way I would be able to integrate this instrument successfully into, for instance, a NMEA 2k via a gateway in the future?

According to NASA this device puts out MWV sentences at 10HZ. That's going to account for about 2/3rds the capacity of a 4800 baud link. You won't flood the capacity of the point to point link from the device to a listener. 4800 baud is insanely slow by modern standards so anything you feed it into will be able to handle the data without breaking a sweat. If you fed it into a multiplexor which combined it with other NMEA inputs and then tried to output everything as NMEA-0183 at 4800 baud, *then* you might overload the capacity of the outgoing link and start dropping sentences but you don't intend doing that.

NMEA 2000 is 50 times faster than 4800 baud NMEA-0183 (although the message format is also different) so you don't have to worry about combining your 10HZ wind data with all your other NMEA-0183 data: an N2K network will handle it.

PaulRainbow has made a few suggestions above about getting your NMEA-0183 data onto an N2K network. It's not just Garmin plotters which will forward NMEA-0183 data to N2K: My old raymarine (C90W) will do it and I suspect most will if they have the right ports. If you don't want to go via a plotter, companies like actisense, quark, shipmodul and yachtdevices make thingumies for connecting one or more NMEA-0183 devices to nmea 2000.

Bottom line: You're fine: you have plenty of integration options

 

[PaulRainbow]

PaulRainbow has made a few suggestions above about getting your NMEA-0183 data onto an N2K network. It's not just Garmin plotters which will forward NMEA-0183 data to N2K: My old raymarine (C90W) will do it and I suspect most will if they have the right ports.

But very few new plotters have an 0183 port.

 

[MattS]

The main extra feature of the Tactical Wind is the ability to give true wind direction providing a suitable speed input was provided. I would think that was worth the £20? There are a number of ways to integrate with N2k so you will be able to do this.

Absolutely right - forgot to mention this! The new wind display will be next to a GPS repeater display, so I'm hoping to just take a split from the NMEA 0183 input into that repeater for the true wind feed.

 

[MattS]

According to NASA this device puts out MWV sentences at 10HZ. That's going to account for about 2/3rds the capacity of a 4800 baud link. You won't flood the capacity of the point to point link from the device to a listener. 4800 baud is insanely slow by modern standards so anything you feed it into will be able to handle the data without breaking a sweat. If you fed it into a multiplexor which combined it with other NMEA inputs and then tried to output everything as NMEA-0183 at 4800 baud, *then* you might overload the capacity of the outgoing link and start dropping sentences but you don't intend doing that.

NMEA 2000 is 50 times faster than 4800 baud NMEA-0183 (although the message format is also different) so you don't have to worry about combining your 10HZ wind data with all your other NMEA-0183 data: an N2K network will handle it.

PaulRainbow has made a few suggestions above about getting your NMEA-0183 data onto an N2K network. It's not just Garmin plotters which will forward NMEA-0183 data to N2K: My old raymarine (C90W) will do it and I suspect most will if they have the right ports. If you don't want to go via a plotter, companies like actisense, quark, shipmodul and yachtdevices make thingumies for connecting one or more NMEA-0183 devices to nmea 2000.

Bottom line: You're fine: you have plenty of integration options

Brilliant - thanks! Basically sounds like not a problem