Mapping Tahina’s Navigation Network

Today I spent a couple of hours trying to map Tahina’s navigation network. I’m doing this in order to determine how best to install the new AIS receiver (it’s a marine transponder system which all ships are required to have). Tahina’s owner’s manual has nice diagrams for all the main systems, EXCEPT the navigation network. Electrical, plumbing (fresh and black), rigging, gas, fuel, etc. all have good diagrams. I wrote St. Francis Marine (Tahina’s builder in South Africa), but they replied with a very basic diagram that was definitely not for our specific configuration.

Tahina’s navigation system is based on Raymarine Marine Electronics (http://raymarine.com). Tahina’s system has a chartplotter, GPS, autopilot, fluxgate compass, lifetag wireless man overboard system, fishfinder, and all the other basic instruments (wind/depth/speed/log/etc.). Also, we have a desktop computer built into the nav station which is plugged into the boat network and has Raymarine’s navigation software. The network is comprised of three different protocols (all with different wiring): Seatalk (the primary instrument network), Seatalk HS (High Speed version), and NMEA (which is an older serial communications system).

Here’s a basic map of a Raymarine network (this is not Tahina’s specific diagram, but it gives you an idea of the complexity – click for larger version):

Raymarine network diagram

The problem is that the AIS unit we have uses NMEA and has to plug into the E120 chartplotter. But, the chartplotter already has something plugged into the NMEA port. And, I haven’t determine what is connected to the other end of that cable. None of the other devices seemed to be using that port (GPS, fluxgate compass, autpilot, lifetag, etc. are all either using Seatalk or plugged in elsewhere). BUT, as I was writing this post, I noticed in the diagram above that one possibile use of the NMEA is DSC (which stands for Digital Selective Calling – and is an emergency broadcasting function on the VHF). I checked, and my radio is connected for DSC. Not only that, but the chartplotter is configured in a non-default mode to allow for DSC messages to be displayed! This may be the solution to the mystery… If so, I need to figure out what to do next – either get a multiplexer so both can plug into the same port, or wire the VHF DSC differently.
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4 Responses to Mapping Tahina’s Navigation Network

  1. Patrick says:

    Not sure why you refer to NMEA as the older protocol…. Also, if you ran a NMEA bus through the boat and hung everything of of it wouldn’t you avoid the issue you seem ot be having of direct connecting everything? You don’t need a multiplexer for that.

  2. Frank Taylor says:

    I said NMEA is older because it is older than SeaTalk or SeaTalk HS. That’s all.
    My understanding, from reading the Raymarine E-120 chartplotter manuals is that the NMEA 0183 data must be directly connected to the chartplotter for some reason. If I could plug both datasources into a junction box and then wire directly to the chartplotter that would be great. But, according to the Raymarine FAQ, you need to use a multiplexer.

  3. Icon Set says:

    Hey the font is kinda small. I’m having to to do the scroll and hold ctrl thing so it looks bigger. Might meet be my browser.

  4. Right now all I can fish for in my area is channel cats and they’re simply boring, dont even get to go out on the boat and try out the new fish finder, just have to take a seat under the bridge.

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