pedestal mounted Raymarine 435i Chartplotter

[Joe Kern]

What would be required to get the Raymarine data to a laptop at the Nav Station?  All my instruments are connected and located at the Pedestal.  Can you run one cable (NMEA 183?) from one of them like the chartplotter back to the Nav station or do you have to run separate cables from each instrument.  Just not sure how to get all that data below and would like to be able to have it at a laptop at the nav station as well as to connect the gps data to the VHF.  Just never really thought about what it would take to do it.

Joe

[Craig Illman]

Joe - NMEA 0183 has limitations because it's 4800 baud. Take a look at this, there are others like it: http://brookhouseonline.com/index.htm

Craig

[rirvine]

Joe:

How one get data from RM (Seatalk) to NMEA is an interesting question which RM does not make easy   The simplest way is to get all the RM instruments connected to Seatlak – get everything on to one pair of wires – and then convert Seatlak to NMEA 183.  The RM Seatalk to NMEA convert box does the sentence conversion OK but does not convert all the fields – have no idea why.   I have no experience with the MiniPlex-42 (http://www.shipmodul.com/en/index.html) that could be a better job at this conversion.

Various RM instruments and displays convert some Seatlak data to NMEA but none that I have convert it all. In my installation, I take the GPS (usingt the WAAS GPS) related data from the NMEA out on the RM chart plotter and the instrument data from an RM converter box both interface to the MAC each via RS-232 to USB converters.   Yes, this does use up two USB ports.

When I start the instrument project, I ran three 1 pair + shield cable from the helm to the Nav station.  Today, one carries Seatlak, one caries the GPS back up data from the NAV 398, and one is not used.

You can see a block diagram of what I have done at: http://www.flickr.com/photos/crews_nest/

This has installation has grown over time. If I was starting with a clean sheet of paper and knowing what I have learned, I would do some thing different.

The fact that NMEA is only 4800 is not an issue (Seatalk is also 4800)

Hope this helps,

Ray

[Craig Illman]

Ray - the 4800 baud is limiting enough that AIS uses NMEA-HS at 38,400 to handle the volume of the datastream.

Craig

[rirvine]

Craig:

The requirement for a higher speed is unique to AIS to deal with the multiplexed AIS data derived from VHF transmissions.  The AIS data is multiplexed onto two VHF channels (question if this will work if AIS B becomes popular) at the source (a ship) and arrive at the AIS receiver as a higher speed stream.  Most AIS receivers have one or more NMEA in connection to allow other NMEA data at 4800 baud (e.g. GPS) to be multiplexed onto it NMEA out.  They also have an option of changing the baud rate of their NMEA out connection.

In the case of instrument and GPS data, RM multiplexes this onto a 4800 baud Seatalk bus using a collision / back off strategy.  With the normal depth, speed, wind, GPS, and autopilot data, there is still a considerable amount to idle time on the Seatalk bus.  Stuff just does not happen that fast on a sailboat.

Ray