Integrating and Documenting NMEA 0183 and 2000 Networks

Central network distribution panel on a McCurdy and Rhodes 56. Multi-conductor cables are run from here to all areas on the boat with navigation and/or communications equipment so changes and additions can easily be made.

Wouldn't you know it, as soon as we put our McCurdy and Rhodes cutter on the market last summer, the Simrad/Robertson autopilot brain that had been reliable for over 20 years and at least 100,000 miles decided to turn its little electronic toes to the air.

And, of course, the new B&G brain I selected—mainly because it is a successor to the old one and therefore compatible with the existing bomb-proof drive comprising a Simrad hydraulic pump and massive ram—is all NMEA 2000, while the old brain was a combination of proprietary connections (Simrad Robnet) and NMEA 0183.

The new brain also came with a new digital compass and needed to be controlled by the B&G Plotter we installed a couple of years back in anticipation of just this scenario, all NMEA 2000.

Easy Peasy

Still, after getting the new kit installed and working, I was confident that getting the networks integrated would be easy and take half an hour or so. After all, I'm an electronics technician by trade and I have been messing with boat networks for 35 years. How hard could this be?

Particularly since we have always kept our NMEA 0183 network well organized with multi-conductor cables from each unit routed into a central patch panel (see photo at top of article) that Phyllis built, documented and labeled—she turns being organized into an art form.

The relatively simple NMEA 2000 network on the McCurdy & Rhodes 56 with the new autopilot and compass added.

And, further, when we added the plotter I documented the simple NMEA 2000 network in Martron's excellent N2K Builder.

Not So Easy

How wrong I was. A few hours into the project about half the electronics on the boat were having a sulk and not talking to the other half, and I was becoming increasingly confused and frustrated as I changed wiring and software settings only to fix one thing but break another.

Time for a deep breath and a rethink.

After staring into space for a while—really hope my mouth was not hanging open as at my age this is a look to avoid at all costs—I realized that the answer to this was to stop changing wiring and settings and instead plan and document the new network first.

A Better Way

And that's what this article is about, an easy way to:

  1. Plan and document
  2. Install
  3. Modify documentation to reflect as built
  4. Iterate steps 2 and 3 until everything works

At first glance the answer would seem to be to draw the whole thing out in the form of a circuit diagram, but actually that's a laborious and error-prone way to go about any wiring documentation, not just networks.

What, you say? Everyone knows a schematic is the way it's done. And yes, that would have been true...up until about 1970. But there's a better way.

Let me explain. Back then I was a mainframe computer technician charged with keeping several new generation room-sized computers functioning—yup, you calculated right, I was 19, it's a long story.

These computers were among the first to have no drawn schematics, primarily because the stack of drawings would have been 20-feet high and impossible to maintain as modifications and improvements were made.

Instead, the entire computer was documented in a few big books of Boolean algebra equations, liberally annotated, with pinouts. Brilliant, and way easier to troubleshoot.

Don't worry, I'm not going to try and teach you Boolean algebra, particularly since I have long forgotten most of mine, but the concept of documenting with written lists, rather than drawings, is the same, and by far the best way to document all the wiring on our boats, not just networks.

To do this we need two documents:

  • A data flow list that shows where each piece of information originates and what devices it goes to.
  • A pinout list that tells us where each wire starts and ends and the position on a junction block or plug as well as what colour it is, so we can quickly go right to it, either to make a change or troubleshoot.

I guess you could try to combine the two, but I find that's both more confusing and time consuming.

By far the best tool I have found to produce both is a spreadsheet, even though I'm really just using it as a table layout app, and not doing any calculation. I use Excel, but Google Sheets or Apple Numbers will do just fine.

At this point I could blather on for thousands of words telling you how to do this, but let's not. Boring, boring, dull.

Instead, let's look at how I quickly resolved my network nightmare above and, without any added effort, ended up with documentation that will make the new owner's life way easier for years to come:

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John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for twenty years, first in yachting magazines and, for the last 18 years, as co-editor/publisher of AAC.

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