Seatalk Option (Seatalk bridge)

Seatalk-NMEA 0183 conversion  option for Brookhouse NMEA Multiplexers

Seatalk is the proprietry  RayMarine protocol for communication between ST Marine Instruments. Brookhouse NMEA Multiplexers support this protocol, as a low-cost optional extra. If the option has been installed, multiplexer input channel 1 can be configured (by the user) for connection of either an NMEA-talker or the Raymarine Seatalk bus. If set up for Seatalk, data is extracted from the Seatalk bus and converted to NMEA sentences. The NMEA sentences are included  in the combined data stream, which is output  from the multiplexer's NMEA port (RS422), the RS232 port and USB. This function is often referred to as a "Seatalk-NMEA bridge". A single cable connects the NMEA Multiplexer with the Seatalk instruments. This single connection gives access to the data, produced by all Seatalk instruments on the Seatalk bus.  Other NMEA talkers can be connected.to the remaining multiplexer input channels.

The Brookhouse NMEA Multiplexer with Seatalk option provides 3 functions in one:

  1. NMEA Multiplexer.

  2. Seatalk-NMEA "bridge" (protocol converter),.Seatalk-USB bridge if the USB option is installed.

  3. Seatalk & NMEA combiner.  

If installed in a Brookhouse multiplexer with compact user-programmable repeater display, Seatalk instrument data can also be displayed on the LCD, i.e. a Seatalk repeater function is provided.

All data in NMEA sentences resulting from the Seatalk-NMEA conversion can be displayed on the LCD. The user can step through the available data displays by repeatedly depressing the LCD pushbutton. Any of the displays can be set as the power-up default,  by depressing and holding the pushbutton until the word "Set" appears.

There are several easy ways of connecting the Brookhouse Multiplexer to the Seatalk bus. The signal can be picked up from any convenient point. Seatalk instruments  have two Seatalk connectors, to enable them to be linked with other instruments in a "chain". The instruments at both ends of the Seatalk chain therefore have an unused connector. One of those connectors can be used to link the Seatalk bus to the NMEA Multiplexer (channel 1, Seatalk option enabled). A standard Seatalk cable with the required length can be purchased from the local RayMarine dealer for this purpose. These cables come with plugs at both ends. One plug has to be cut off so that the bare wires can be  inserted  in the screw-terminals on the Brookhouse multiplexer.

 

                          

If an autopilot is part of the Seatalk system, the AP controller also provides a convenient connection point.

The connection can also be made without the special cable, by cutting an existing Seatalk cable that connects 2 instruments and by making a simple splice. Click here to see how.

The  Seatalk to NMEA conversions performed by the Brookhouse multiplexer include GPS and all essential instrument data. The NMEA output has been tested with many navigation software products and chart plotters.  

The user can select the generated NMEA talker ID in the multiplexer setup menu. II is the standard mnemonic for "Integrated Instruments"..

If necessary, the filtering and editing feature, which is standard for all Brookhouse multiplexers, can also be applied to NMEA sentences that are the result of the Seatalk to NMEA conversion. 

The following Seatalk data is extracted from the Seatalk bus and converted to NMEA by the Brookhouse Mux Seatalk option:

 

Brookhouse Seatalk-NMEA Bridge conversions

Speed log instrument
Seatalk code Description Resulting NMEA Sentence Comments
20 Speed through water VHW Combined with heading if available
26 Speed through water VHW Combined with heading if available
21 Trip mileage VLW  
22 Total mileage VLW  
23 Water temperature C and F MTW  
27 Water temp.  C and F  0.1 acc. MTW  
25 Total trip and log VLW  
Depth sounder instrument
00 Depth below transducer in meters DBT  
00 Depth below transducer in feet DBT  
Wind instruments
10 Apparent wind angle MWV & VWR  
11 Apparent wind speed  in knots MWV & VWR  
Fluxgate Compass (from Autopilot)
84 Compass Heading HDM & VHW Combined with speed through water in VHW
GPS
50,51 Latitude / Longitude of position RMC
52 SOG (Speed Over Ground) RMC
53 COG (Course Over Ground) RMC, VTG In RMC: True course (Compass Variation applied) 
54 Time (GMT) RMC
56 Date RMC
99 Compass variation RMC Is applied to magnetic course for true COG in RMC sentence

  Note:  Seatalk is a trade-mark of RayMarine.