NMEA 2000 and all that stuff!
When we got Dulcinea she had a fairly normal Raymarine instrument setup from about 10 to 15 years ago – still working, probably as well as when new.
Here is the equipment that was on board:
VHF radio – not licensed and not able to transmit as no DSC set.
Chartplotter Raymarine C90W (Nav table) with Seatalk and SEATALKng interfaces
Furuno GPS receiver (Nav table)
Furuno Navtax receiver (not working – Nav table )
Raymarine Autopilot ST7000 and associated equipment
ST60 Wind, ST60 depth (bridge deck) and ST60 Multi (nav table) displays.
Since this setup is a legacy from the time when paper charts were still a part of navigation it is based around navigating from the Nav station below, whereas with the wider integration of electronic navigation navigation under way is usually from the cockpit or under the sparay hood. So my two primary targets were to fit AIS, both receiver and transmitter ( in my view an AIS transmitter is a vital satety feature) and facilitate cockpit navigation. During our many charters in Scotland we had had various chart plotters on board, but as each had a different user interface so we had never really bothered to learn to use them,relying instead on a tablet with Navionics as our primary tool, reverting occasionally to the chartplotter below if we needed AIS – although there were never any occsions when we really needed it as shipping is very sparse around the Hebrides and visibility usually fair to good.
First priority was to sort out the VHF and AIS and the antennas – its usual to have a separate VHF radio and AIS transponder unit unless you just want to receive AIS and not transmit your position data. If you just want the receive only AIS function on a VHF radio it will normally use the same antenna as the VHF, but its not permitted under UK regulations for a single unit to act as a AIS transponder and a VHF radio with a single antenna. Also an AIS transponder must have its own dedicated GPS receiver with or without an external antenna.
Most boats seem to function with a single antenna at the masthead that is used for both VHF and AIS transmissions using a separate antenna combiner to link the separate VHF and AIS transmitted outputs. While this works reasonably well, its not ideal as the VHF channel 16 and AIS are at opposite ends of the VHF spectrum so an antenna used for both is a compromise. This arrangement usually means that the boat has no fixed alternative antenna in case of emergency, for instance dismasting, instead if the crew are lucky, having an inflatable temporary antenna.
Dulcinea’s solution was to install a B & G V60-B VHF radio with integral AIS transponder with the necessary separate antenna outputs for each function – its the only VHF available with this function ( except the Simrad identical product) We have a Glomax dedicated AIS antenna mounted on the outboard motor derrick on the stern rail, and the normal masthead VHF antenna. I also installed a Quark antenna combiner so we have the option of using either antenna for either or both functions – AIS transmissions are a safety feature ,in an emergency as they allow help to home in on you withut plotting Lat and Long., so ideally you do need both AIS ans VHF. Our AIS antenna, being only about 4 meters above the sea won’t have as long a range as a masthead antenna would give, but it should work out to about 5 miles or so – quite enough for normal use.
Ar this point we come up against the thorny issue of boat data networks, which can be a bit of a puzzle, so here is a brief guide:
NMEA 0183 : Early on in the boat electronics era the marine industries standardised a simple system to digitally connect various devices on a boat – NMEA 0183. This lets one device on the network transmit standard text sentences that can contain multiple data values separated by commas, and other devices to receive these sentences and decode them. There are hundreds of standard messages, including many that duplicate a lot of the data transmitted by other messges – particularly those relating to position data from GPS. NMEA0183 is quite slow and used coding based on the old standard electronics communication protocal RS232.
SEATALK : A proprietory RAYMARINE system that is based on NMEA 0183 but with enhancements to allow it to operate as a more effective network – its not particularly difficult to connect NMEA and SEATALK systems as the both use exactly the same sentences for almost all functions, and code it in the same way. It is used in all the old RAYMARINE ST60 units for example, and has its own proprietory connectors – its easy to connect up old RAYMARINE devices using SEATALK.
NMEA 2000: This is the successor to 0183 as that network had severe speed limitations in its standard form – even the output of an AIS receiver could overaload it. NMEA 2000 is a proper network allowing many different devices to communicate seamlessly. Unlike the earlier networks, 2000 doesn’t use sentences, but ‘words’ that contain a single data value or a set of closely related values. NMEA 2000 is a marine standard that used its own ‘words’ sent and received using an underlying established network protocal called CANBUS that is used for connecting the many digitally controlled functions of all modern cars. NMEA 2000 uses its own specific cabling and connectors, and is designed, like SEATALK was, to power devices from the network wiring, so a network only requires a single power input. Note that NMEA2000 networks must be terminated at each end with a plug containing a 120 ohm resistor – a TERMINATOR.
SEATALKng is the modern RAYMARINE equivalent of NMEA2000, using pretty well all the same standard ‘words’ and underlying CANBUS architecture but with slightly different connectors and cabling – probably to allow for future video as part of SEATALKng. Conversion from NMEA 2000 to SEATALKng is just a matter of an adaptor cable with different plugs on each end. There is,however one annoying difference between NMEA 2000 and SEATALKng – the NMEA uses all male connectors on the backbone and on the devices so all the drop cables are male to male, whereas SEATALKng uses different gender connectors on each end of the drop cables, which in my view makes interconnecting things unnecessarily confusing!
SEATALK to SEATALKng is simple using a small network junction – RAYMARINE part E22158 – that lets you plug in the SEATALK and does all the conversions back and forth between SEATALK /NMEA0183 sentences and SEATALKng/NMEA2000 words. It has provision for 2 SEATALKng devices to be connected, as well as a link to another part of a SEATALKng or NMEA2000 network depending on what connecting cable is used. It also has a connector for a terminal resistor. Note that the SEATALK network normally has power as well as signals on its banana shaped plugs, and if the SEATALK to SEATALKng cable supplied is connected into the E22158 will power up the whole network without any additional power inputs – at least it does on my setup!
Having got that out of the way, here is what we needed on Dulcinea;-
Add an ORCA app running on a tablet computer and an ORCA CORE2 to use as a main navigation system – this needs NMEA2000 to connect to the existing devices and the new VHF.
Add a Yacht Devices NMEA 2000 Engine interface so engine data ( Temperature, Revs, Alternator and Battery voltage are available at the helm and on any tablet on the system.
Retain Raymarine chart plotter C90W at the Nav station as it acts as a display for the Radar, and functions as a back-up for charting, although the charts haven’t been updated in years. It used a a Furuno AIS receiver that is now redundant and so it needs to be linked to the NMEA 2000 AIS data from the VHF
Retain all ST60 wind and depth and autopilot units on the old SEATALK network
Interconnecting this didn’t present any problems except for finding a route for the Engine interface NMEA2000 lead into the engine bay as the cable entry was packed – in the end I had to cut the cable, push it through and rejoin it as the connector was too big to pass through the duct with all the existing wires.
Connections were as follows;
E22158 SEATALK to SEATALKng converter connected to the existing SEATALK network and Chart plotter connected to one of its SEATALKng inputs. Terminal assed, plus a link conversion cable to a 4 outlet NMEA 2000 bus that has inputs from the B & G VHF, ORCA Core2 and the Engine interface. I initally connected a power inlet cable to the NMEA 2000 4 outlet bus, but discovered that it was also getting power from the old SEATALK network when the autopilot was turned on.
As we want to be able to use the ORCA core and and AIS receiver when at anchor without having the autopilot and other nav instruments powered up we will leave two power souces and put a power isolator between the SEATALKng and NMEA2000 networks.
to be continues