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  #1  
Old 03-05-2014
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Help me understand nmea 2000 and electronics.

So I've been reading some and it really sounds complicated. But I've got to learn it so that when something goes down I will know how to troubleshoot it.

I'm gathering that n2k is a new way for different systems to talk to each other. Say a lowrance chartplotter can display a raymarine windtransducer which can send the wind direction to an autopilot. Where before these systems were all separate. Your chartplotters chartplotted. Your depth transducer sent the signal to a box like a hawkeye designed for that specific depth sounder.

I also know you have a backbone. Which is a long waterproof high end cable with connectors for each device. That's where my knowledge ends. I don't know if they talk to each other through the cables or through Bluetooth or wifi or whatever. There is also Ethernet which remains elusive.

I just discovered panbo website but think its more for electronics hobbyists to discuss the latest tech. I'm not really an electronics hobbyist. I just want my systems to work, to know what to do if something isn't, and to be competent to add something if need be.

Are there any good websites that teach you about marine electronics? Someone's blog of designing or installing their own n2k system? Any resources you feel valuable I would be glad to take a look at.
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Old 03-05-2014
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Re: Help me understand nmea 2000 and electronics.

It communicates through the backbone cable. The cable can also supply power to some devices. The idea of NMEA 2000 compared to NMEA 0183 is that it is much simpler to connect devices. Mostly plug and play.

More info at nmea.org
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Old 03-05-2014
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Re: Help me understand nmea 2000 and electronics.

Oh it is also the power supply. Of course. I should have thought of that. Makes me look stupid or shows my lack of understanding electronics. But I'm getting better.

What if you have say a fuel tank moniter. How is that powered and sending information?

If you go nmea does everything have to be nmea or can you mix?
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Old 03-05-2014
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Re: Help me understand nmea 2000 and electronics.

NMEA 2000 is a NETWORK based on the automotive CANbus architecture and protocol. It enables many devices to communicate with each other over the network. See

NMEA 0183 is a serial protocol based on serial line EIA-422 (aka RS232) and special ASCII sentences which are specific to the NMEA syntax. It is PAINFULLY slow compared with NMEA 2000, and requires that baud rates for any devices that are to communicate be set to the same speed.
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Old 03-05-2014
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Re: Help me understand nmea 2000 and electronics.

It's easiest if everything that you want to have talk can all talk over NMEA 2000. Mixing and matching NMEA 0183 and 2000 can work, but you need to have a device that can do the translation (usually this is the MFD) and there is latency between them.

You don't need NMEA if you just want a very basic system. There are plenty of chart plotters that have built in fish finders and don't have any NMEA networking functionality. Lowrance Elite 5 and Raymarine Dragonfly are examples of this. Most plotters/GPS under $500 will be of this type.

A simple system that would be common on a small sailboat would include 3 devices:
* plotter with depth
* speed transducer (to get through the water speed)
* VHF with AIS receive capability

The depth transducer would plug directly into the plotter using proprietary wiring. The speed and VHF would both plug into the plotter using NMEA 2000.

The nice thing about NMEA is that you can expand the system to include more devices and have them all interoperate. For instance you might later want to add an autopilot, and it could talk to the existing network to steer to a waypoint on the plotter. Then a year later you might add a wind instrument and it could interoperate with the autopilot and plotter to support steering to a wind angle instead of to a bearing.

NMEA 2000 backbones don't need to be complicated. My NMEA 2000 network has gotten more devices than I originally expected. The backbone runs from the pedestal down to where the autopilot and transducers live (under my quarterberth) and finally over to my main electrical panel where the VHF and NMEA 2000 power exist. It isn't a complicated backbone that snakes all over the boat.
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Re: Help me understand nmea 2000 and electronics.

Quote:
Originally Posted by eherlihy View Post
NMEA 0183 is a serial protocol based on serial line EIA-422 (aka RS232) and special ASCII sentences which are specific to the NMEA syntax.
NMEA 0183 is also point to point and requires multiplexers to add additional devices. NMEA 2000 is a bus network and additional devices can just be plugged in, no electronics are necessary to get additional ports and add additional devices.

I can't imagine using NMEA 0183 for a new deployment today.
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Re: Help me understand nmea 2000 and electronics.

Why the need for the speed transducer when the GPS tells how fast you are going?
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Re: Help me understand nmea 2000 and electronics.

GPS tells you how fast you are going over the ground below. Speed transducer tells you how fast you are going through the water. If you in a high current area then there can be a significant difference.

I find both useful to know, but if I could only have one it would be GPS speed since that is cheaper and easier to get these days.

This photo was taken when our GPS speed was almost 11 knots, but boat speed was 5.8 knots (a typical cruising speed for my boat):
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Re: Help me understand nmea 2000 and electronics.

So for instance. Say you were fighting the current. You may be sailing very efficiently and movin through the water at 6 knots, but speed over ground might be 2 knots. Or the opposite. If you are going with the current you could be sailing again at six knots, but moving over ground at 11? Is that right?

If so why is the sore through the water important, wouldn't you really only care what kind of forward progress you are making?

I do feel like I am missing something here.

On ais. I did read a short article on AIS. My understanding is all big ships, the ones you don't want to hit in the fog, register their call sign and show up on ais. So say you have a vhf with ais like the standard horizon 2150. The nmea will link it to your chartplotter and those will then appear on your chart. Showing where they are and where they are heading. You can also go to sleep and set an alarm if you are in the middle of the ocean and it will alert you when a ship comes close. Yes? If that is how it works I completely see the value in it. Especially for the cost. It's not nearly as expensive as radar.

But radars benefit is it detects metal objects and has greater range. Plus it sees weather? I haven't looked into radar yet. That is not on my list for this year.

Thanks as always or the help. I'm getting this. Believe me. Im not stupid. I've just spent the majority of my life not being interested in tech. But I've got the tech bug now. I think years ago getting my iphone was what started it. I really was impressed. I didn't know they were so much more than phones and loved the fact that I could look things up anywhere I was.

I got my first digital camera recently. That I am actually picking up super quick. Maybe because a lot of what I'm learning isn't tech stuff. But things like aperture, shutter speed. I grasp these things lightning fast.
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Last edited by northoceanbeach; 03-06-2014 at 12:49 AM.
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Old 03-06-2014
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Re: Help me understand nmea 2000 and electronics.

It is nice to see if you are sailing your boat to its optimum speed. You could be making 5kts sog with poorly trimmed sails and 3kts of set. Good trim and you are now making 8kts. Really easy to see when you are doing it right and when you're doing it wrong.
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