Terrapin Electronic Upgrade, Part I

Installing an N2K system

When I bought Terrapin in 2017, she had original equipment (1997) gauges based on the 0183 protocol and didn’t even have a wind speed/direction sensor at the top of the mast.  The electronics consisted of original equipment Raymarine speed/depth transducer, autopilot, and an old Garmin GPS chartplotter.  Over the ensuing three years I have completely re-done the electronics and installed an N2K network. The only thing I really wanted/needed at the time was wind speed/direction at the top of the mast.  Terrapin is a sailboat after all, and knowing wind speed/direction is pretty important.  As I started doing research on mast-top wind sensors, it became apparent that N2K was the way to go.  Even if I didn’t do everything at once, N2K would allow me to add new instruments and sensors at a later point.  Of course, in order to see the wind speed/direction display, I would need a new display and I decided on the B&G Zeus 2 multi-function display (MFD).

If you have spent any time reading about or using boat electronics, you are probably well aware of NMEA 2000.  In a nutshell, NMEA 2000, abbreviated to NMEA2K or N2K and standardized as IEC 61162-3, is a plug-and-play communications standard used for connecting marine sensors and display units within ships and boats. Physically, it consists of a “backbone” cable capable of transferring data and small current, kind of like USB, and way of connecting all sorts of sensors and instruments to the cable through tee connectors and drop cables, all using an industry standard connection plug and data packet protocol. N2K has been around for about 20 years, but there are still a lot of boats with pre-N2K electronics based on the old NMEA 0183 protocol. As these electronics begin to fail, the owner will need to consider adopting an N2K system.  You don’t have to replace everything as 0183 instruments can work with N2K using 3rd party adaptors.  

Backbone vs drop cables, Ancor Marine
N2K power tee, Ancor Marine
N2K tee, Ancor Marine

An N2K system is very much a DIY project for a boatowner as long as you do some reading and follow some basic rules. The main components of the N2K network are the backbone cable, tees and drop cables going to each instrument/sensor, a specialized power tee to provide low amperage 12V power to the network, and a terminator at each end of the backbone. The length of the backbone is limited to about 100m while each drop cable is limited to about 5m or 16 feet. This basic backbone can be hooked up to a multi-function display, individual displays, a laptop, or even WiFi using appropriate adaptors. It is easily adaptable to both small and large boats.  Because the network is energized with 12Vdc, many devices, particularly low amperage sensors, do not need to be wired separately to 12V. The N2K drop cable provides all the power they need.  Other devices that require additional current to operate, like autopilots, displays, and AIS, will need to be wired separately to a 12V source in addition to the drop cable.  N2K is not particularly high bandwidth and is not designed for transmission of radar or video.  One other important consideration in designing an N2K system is that there are male and female connectors.  Each section of drop cable will have one male and one female connector at either end.  Likewise with tee connectors. The straight line part of the tee is designed to attach to the backbone, one male and one female end. Thus, the length of the backbone is directional. The right angle part of the tee is designed to attach to a drop cable and is female.  Terminators are either male or female.

N2K female (top) and male (bottom)

I started the N2K installation on Terrapin with the purchase of the B&G 508 wind sensor. This sensor actually came bundled with 20m of N2K backbone cable and included a terminator.  Because of the length limitations of the drop cable, the backbone must start at the top of the mast if you want to attach mast mounted instruments to your N2K network. Thus, the wind instrument at the top of the mast became the first instrument attached to the backbone. Running the backbone cable down the mast was the most difficult part of the whole installation and I had two pros doing it while they were rigging my new roller furling! The backbone should then be routed through the boat such that every instrument or sensor that you might want to ever attach to the backbone is no further than 16 feet from backbone cable.  It is best if you can identify a few zones where groups of tees can be attached. In my installation, there were obvious zones at the nav station behind the breaker panel, a locker below the cockpit, and a locker near the stern.    

N2K cable

The one mistake I made in designing my N2K system was that I used the single 20m backbone supplied with the wind sensor for entire length of the N2K backbone.  This meant that I had to cut the cable twice to insert tees at two of the zones. This required the installation of four N2K connectors. This didn’t seem to be a problem because you can buy “field attachable connectors” from a few different suppliers. I bought the ones sold by Maretron. They make it seem easy to do the attachment but, believe me, it is not!  The N2K cable contains 4 insulated wires, one non-insulated wire and a metal sheath, all of which need to be connected to little screws within the connector.  To make matters worse, the non-insulated wire needs to be insulated with a tiny length of heat shrink tubing so it doesn’t short out on the other terminals.

The rigger installed the wind sensor at the top of the mast and then fed the N2K backbone down the mast into the cabin using a messenger wire.  Even without a connector, the cable was difficult to feed through a narrow spot at the deck.  I then pulled the entire 20m of cable down through the mast and routed it through the starboard side of the boat, through the nav station and back to the stern.  I then cut the backbone at the locations where I needed tees and set about attaching the field attachable connectors.  This was difficult and time consuming and, as I was to find out later, I obviously messed up at least one connector because the network didn’t work. 

Next, I connected the power tee and wired it to the Instruments breaker at the nav station.  Then I installed a tee in the locker by the cockpit helm and fed a drop cable to my new Zeus 2 MFD.  The Zeus 2 was also wired to 12Vdc per the instructions.  One of the great things about the Zeus is that it has a built in Network Analyzer, and it was immediately apparent that there was a problem with the N2K network.  Since I was not very confident in my field attachable connectors, I suspected these were the cause of the problem. I decided to replace these sections of backbone with shorter cables with factory installed connectors.  I purchased these cables as well as extra tees through Ancor Marine.  This left my network with only a single field attachable connector at the end of the section of backbone that was routed through the mast.  This one was apparently a good connection because the network worked fine once I made this change.

 At this point, I had a working N2K network with only wind speed/direction and a Zeus 2 MFD, but with the ability to add devices and sensors as desired. I sailed Terrapin for a season with this setup and got familiar with using the Zeus chartplotter with its great SailSteer wind display.  Over the next two sailing seasons, I added a Vesper AIS transponder, a B&G autopilot, B&G 4G Radar, and a B&G depth/speed/temp transducer.  For each addition, all I had to do was to add a tee, or multiple tees in the case of the autopilot, to the backbone cable and install the instruments. In each case, the Zeus immediately recognized the added device and also provided the interface to perform calibrations and set other options for each device.  While it is possible to mix and match brands on the N2K network, there are also proprietary signals sent through the N2K network and I believe this is why my B&G system worked so seamlessly.  That being said, I do have one non-B&G device, the Vesper AIS transponder, and that also works flawlessly.

In summary, when designing your N2K network, first decide the locations in the boat where you will need one or more tees and then purchase separate lengths of backbone with factory installed connectors.  You might need to remove a connector to route the cable through the mast or a tight channel, necessitating the installation of a field attachable connector, but try to minimize this.  Connect the sections of backbone with one or more tees, provide 12V DC to the power tee, and add a terminator to each end.  Finally, a good MFD like the B&G Zeus to tie everything together is one of the best ways to set up your network.

The Zeus 2 Multifunction display. Current display is showing windows for the autopilot (left), chartplotter (middle) and SailSteer (right). The chartplotter shows the location of Terrapin (black boat shape) and also other vessels broadcasting an AIS signal (open triangle).

For the helm and the brains of the system, I installed the highly rated B&G Zeus 2 MFD.  It comes in 7”, 9” and 12” and I chose the 9” display because it fit perfectly at the helm. These MFDs have the capability to customize windows to display virtually any data present on the N2K system. The most important display is the chartplotter, which shows a nautical chart with your GPS location and the ability to zoom in and out.  If you add radar to the system, it will overlay the radar on the chart so you can see exactly what is around you relative to charted objects.  If you add an AIS receiver, you can view other ships on the chartplotter that are broadcasting AIS information.  The MFD also has a sophisticated control system to run the autopilot and to set navigation routes.  The B&G Zeus also has a great panel called SailSteer with key sailing data including vessel heading, wind direction (apparent and true), wind speed (apparent and true), GPS course over ground, speed over ground, etc.  There is a ton more that these MFDs can do, but you get the idea.

Terrapin N2K wiring diagram

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