Creating an Electronics Roadmap for your Boat

Tech Talk – February 2020 – Electronics Wiring Diagram

As boaters, many of us benefit from navigation electronics to safely discover new destinations and return to favourite ones. The integration of devices is commonplace, for instance, connecting a VHF radio to a GPS receiver for latitude and longitude coordinates when calling a VHF distress call. Or sharing depth information between multiple navigation devices so that a boater can safely negotiate shallow passages on all the electronics throughout the boat. The integration of navigation electronics is one of the main features of a modern navigation system.  The benefits of integration also comes with a duty to accurately document how all of this integration is accomplished. Unfortunately, it's still pretty uncommon for a boat to have navigation electronics schematics, detailing what is connected to what.  This drawing is increibly valuable when troubleshooting navigation system issues, for instance, answering a common troubleshooting question like "why is bottom depth suddenly not showing on my chartplotter?"

Unfortunately, far too many boats don't have a navigation electronics schematic even though they have an integrated navigation system. Putting together a simple diagram of your boat's electronics system may seem overwhelming, but it isn't as hard as you think.  It just takes time, patience, and the realization that it cannot be completed in a day and will be an on-going project.

Where to Start? Begin with a large sheet of paper and start by identifying the individual navigation components such as the chartplotter, VHF radio, AIS, radar, autopilot, depth sounder, etc.  A good tip is also to write down the model numbers and serial numbers of the electronics. 

Next, you will need to identify how everything is connected or not.  Do you have a serial network and/or backbone that connects each of these components and allows them to share information?  The National Marine Electronics Association (NMEA) was formed by a group of electronics dealers to grow their relationship with the electronics manufacturers. As technology started to take off in the marine industry, the association realized that there must be some way for equipment, from different manufacturers, to share information.    NMEA 0183 is the most prevalent network we see on boats built before the early 2000s; however, most boaters never really realized the full benefits of interconnecting many electronic devices on board because of the difficulty of implementing NMEA 0183 serial connections.  In most NMEA 0183 installations, it was used to connect a VHF radio to a chartplotter for GPS coordinates or used to integrate an autopilot to a chartplotter to share heading waypoints and routing information.

NMEA 0183 or NMEA 2000.  For the average boater, NMEA 0183 was not plug and play nor straight forward to install.  With the increased need to share data across more and more devices, the newer NMEA 2000 was developed to allow any device to talk and listen to any other device.  NMEA 2000 is closer to “plug and play” ready, scalable, and much easier to install. Unlike NMEA 0183, which uses a serial connection, NMEA 2000 uses a Controller Area Network (CAN) bus network, which allows all parts of your boat to communicate with one another. NMEA 2000, also known as N2K, replaces all of the NMEA 0183 wiring and interconnections with one single cable backbone.

The data that can be shared over NMEA 2000 is nearly endless.  If there is an N2K sensor, it can be shared.  Everything from wind speed, barometric pressure, GPS position, AIS targets, fuel flow sensors, smoke detectors, engine data, bilge levels, you name it.  Manufacturers have even created converter devices that allow for NMEA 0183 to NMEA 2000 and vice versa to share info across both NMEA networks.

If you are thinking of upgrading or re-organizing your navigation equipment, then it may be an excellent time to install an NMEA 2000 backbone.  It can be a DIY project; the trick is to start with a diagram.  We recommend drawing all of the devices at the bottom of the page in the order that they appear on your boat from forward to aft.  The trick is that each device can only be six meters from the backbone cable.  The other trick is to ensure that there are only two terminators, a male terminator at one end and a female terminator at the other.

Ethernet.  While the NMEA takes care of lower speed sensor networks, Ethernet is still required for high-speed data like radar, sonar, sharing charts, and video cameras.  Besides NMEA 0183 and NMEA 2000, many chartplotters, sounders, and radars are interconnected to one another via proprietary ethernet connections. It's important to know how this ethernet navigation network is wired. For instance, where is your radar ethernet connection terminated? Does it connect directly to a chartplotter or a switch? A network switch is a device that allows multiple network devices to talk to one another. On some boats, all compatible network devices are connected to a switch. On other boats, there is no standalone switch, and the chartplotter serves as the switch. (i.e., since the chartplotter has more than one ethernet network port). Ask yourself, how are my chartplotters interconnected?  What about the black box sounder, how is it connected?

To complete the schematic drawing, you will have to figure out what each wire is for and where it goes.  Once you have established the purpose of the wire, attach a label to identify it.  Use a high-quality labeler as oils and moisture in the air can cause most home office labels to dissolve.  While you are tracing each wire, look for signs of chafing or small bumps and change as required. 

Many electronics problems start with the connectors; the wires are in a damp environment and are subject to constant vibration.   Spending the time to create an electronics schematic also serves as an excellent time to familiarize yourself with the gear on board while performing some valuable maintenance.  As John F. Kennedy said, “The time to repair the roof is when the sun is shining.”

About the author: Jeff Cote is the owner of Pacific Yacht Systems, a full service shop delivering marine electrical and navigation solutions for recreational boats. Visit their website and blog for info and articles on marine electrical systems, projects and more: