Teranodon
Member III
<style type="text/css">p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px 'Helvetica Neue'; color: #454545}p.p2 {margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px 'Helvetica Neue'; color: #454545; min-height: 14.0px}</style>When I installed a Raymarine EV-100 wheel autopilot, I had to set up a simple SeatalkNG data network to link all of the pieces together. Later, I acquired a Garmin EchoMap 54CV CHIRP chart plotter. I ran it in stand-alone mode on top of the pedestal, i.e., with nothing more than a 12V power connection. Finally, I got a Garmin 210 VHF radio. The radio picks up AIS signals, and can display the targets on the Echomap, but the two devices have to be connected via a Garmin NMEA 2000 network. I was going to put together the basic pieces for that, but then I thought: isn’t it kind of dumb to have two networks on one boat? So I did a bit of research and discovered that it would indeed be dumb. As it turns out, the “proprietary” data networks from companies such as Simrad, Raymarine and Garmin, are essentially identical and, in theory, interoperable. But they use different connectors. By doing some splicing and soldering, I was able to hang my two Garmin units on the existing SeatalkNG system, as follows.
(Before going on, I apologize to the many Forum members who already know all this. In fact, it’s not such a big secret).
The basic network architecture is simple. A single backbone runs through the boat. It consists of segments of cable that are joined by T-connectors. Each T-connector links to a device (sensor, chart potter, display, radio, etc.) with a “drop cable”. The backbone (and the drop cables) have four wires: signal high, signal low, +12V power, and power ground. At one place, 12V DC power has to be supplied to the backbone (again, using a T-connector). On each end of the backbone, one has to insert a termination resistor. That’s it. The only way in which the components from different manufacturers differ is in the connectors (sex, pin layout) that go on the T’s, the backbone and drop cables, and the terminators. There are special T’s that support several drop cables. Here is my new system:
The network includes 12V power, but only certain low-power devices can use it (for example, the display for the autopilot). The autopilot drive, the radio and the chart plotter all need separate power connections, each with a circuit breaker. Makes sense.
Looking at the cables that came with my Raymarine units (autopilot, speed, depth, wind) and Garmin units (chart plotter, radio) I concluded that I needed to create “hybrid” drop cables with a female Garmin connector on one end, and a Raymarine female connector on the other. Regular Garmin drop cables are male/female. (NB. despite the best intentions, all connectors in this posting are cis-gendered).
I had to buy a couple of NMEA 2000 drop cables, and a SeatalkNG T-connector. In the end, I didn’t save much money by combining the two systems.
I struggled for a couple of hours with the hybrid cable that just wouldn’t go down the ridiculous 1-inch Edson pedestal guard (I had to do the splicing in the quarterberth, underneath the pedestal). I put it all together and powered up with some trepidation. No worries! Now I have AIS targets all over the place, and alarms going off for a potential collision with every barge and ferry that approaches my marina.
The manufacturers like to pretend that their proprietary networks are unique, and they want you to buy their hardware. I talked to the (normally helpful) Garmin technical assistance people, and they got very snippy when I asked about integrating their devices onto the Raymarine network. In general, there seems to be a lot of hype in this domain. Thus, company literature likes to grandiosely refer to the backbones as “transmission lines”. In reality, I suspect that they are far less than that. The rise times are too long, the propagation distances too short and, anyway, a pair of humble copper wires hardly qualifies. The vaunted termination resistors on each end of the backbone are probably there simply because that is what the drive circuits expect to see in, essentially, mundane DC operation.
So the bottom line is that (except for some exotic devices) slicing and dicing of cables should work for any brand of NMEA 2000 compatible network. You can even buy the hybrid cables, but they come in fixed lengths which isn’t always what is needed.
(Before going on, I apologize to the many Forum members who already know all this. In fact, it’s not such a big secret).
The basic network architecture is simple. A single backbone runs through the boat. It consists of segments of cable that are joined by T-connectors. Each T-connector links to a device (sensor, chart potter, display, radio, etc.) with a “drop cable”. The backbone (and the drop cables) have four wires: signal high, signal low, +12V power, and power ground. At one place, 12V DC power has to be supplied to the backbone (again, using a T-connector). On each end of the backbone, one has to insert a termination resistor. That’s it. The only way in which the components from different manufacturers differ is in the connectors (sex, pin layout) that go on the T’s, the backbone and drop cables, and the terminators. There are special T’s that support several drop cables. Here is my new system:
The network includes 12V power, but only certain low-power devices can use it (for example, the display for the autopilot). The autopilot drive, the radio and the chart plotter all need separate power connections, each with a circuit breaker. Makes sense.
Looking at the cables that came with my Raymarine units (autopilot, speed, depth, wind) and Garmin units (chart plotter, radio) I concluded that I needed to create “hybrid” drop cables with a female Garmin connector on one end, and a Raymarine female connector on the other. Regular Garmin drop cables are male/female. (NB. despite the best intentions, all connectors in this posting are cis-gendered).
I had to buy a couple of NMEA 2000 drop cables, and a SeatalkNG T-connector. In the end, I didn’t save much money by combining the two systems.
I struggled for a couple of hours with the hybrid cable that just wouldn’t go down the ridiculous 1-inch Edson pedestal guard (I had to do the splicing in the quarterberth, underneath the pedestal). I put it all together and powered up with some trepidation. No worries! Now I have AIS targets all over the place, and alarms going off for a potential collision with every barge and ferry that approaches my marina.
The manufacturers like to pretend that their proprietary networks are unique, and they want you to buy their hardware. I talked to the (normally helpful) Garmin technical assistance people, and they got very snippy when I asked about integrating their devices onto the Raymarine network. In general, there seems to be a lot of hype in this domain. Thus, company literature likes to grandiosely refer to the backbones as “transmission lines”. In reality, I suspect that they are far less than that. The rise times are too long, the propagation distances too short and, anyway, a pair of humble copper wires hardly qualifies. The vaunted termination resistors on each end of the backbone are probably there simply because that is what the drive circuits expect to see in, essentially, mundane DC operation.
So the bottom line is that (except for some exotic devices) slicing and dicing of cables should work for any brand of NMEA 2000 compatible network. You can even buy the hybrid cables, but they come in fixed lengths which isn’t always what is needed.
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