NAC-3 B&G Autopilot Computer Installed

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…The B&G NAC-3 Autopilot Computer…

Today was day three of our rebuild / installation work and we spent all day on the NAC-3 autopilot computer installation. This required making all the connections in the sail locker while crouched in a seated position leaning back at about a 45 degree angle. The sail locker is under the cockpit seats and to get into this space you first have to empty the locker. Then once all the stuff is out and scattered around the cockpit, you climb over that stuff and drop down into the locker which is about 7 feet long, 4 feet wide and maybe 4.5 feet deep. The floor slopes downward because you are against the hull. Each time I go inside, I realize I forgot some necessary tool. Not to worry, that is where Radeen jumps in. She is a great assistant grabbing tools and providing uplifting moral support. We are doing all this install work together, as a team, and that way we both know exactly how it is built. Today we were excited when we made the final Tee connection for the GPS drop and the rudder reference and the compass9.

Setting up the tees and preparing for backbone in the sail locker

Our next task is to set up the entire NMEA 2000 backbone which will start at the top of the mast, come down the mast to the mast base below the floor outside the head where it will connect to the wind anemometer and the radar. Then it will run under the head floor and down the port side to the nav desk where it will pick up the AIS transceiver and the Triton2 display. From there, it will run under the floor to the quarterberth floor and pick up the DST 800, the depth, speed, temperature sensor. Then off into the engine room and around the corner into the sail locker connecting to the four Tees at the NAC-3. Next, it will go under the cockpit floor and turn up into the helm guard tubing and run up to the NavPod at the helm. There it will tee into the Zeus2 Chartplotter and radar screen, the Autopilot Controller and one more Triton2 display head. The backbone will then terminate in the navPod. The other resister that terminates the backbone will be in the mast head built into the wind anemometer. This backbone run should be the easiest part because we pulled chase ropes when we pulled out all the old wires. That was a smart move. So, onward we push as we build the backbone and learn about the system.

Here are some photos….

The computer and all the connections
Notice the drawing is backwards with the screws on the top….errror.
My wiring is correct and the part is correct, I need to alert B&G.

I wired the NAC-3 upside down as it was easier to make the connections.

There it is, all connected. the power, drive ram, ground wire and NMEA 2000

The diagram on the NAC-3 door

Working in the sail locker on my back with NAC-3 on my knee

Once wired, we mounted it to the wall where the old ACP-1 was located

This is a NMEA 2000 Maretron Wire bundle, pairs are shielded

We had to cut one end of the GPS feed and install our own NMEA 2000 end

4 wires with one screen, Red/Black & White/Blue + Screen

The end fitting installed

The end was needed to make our GPS connection to the network.

We have never built a NMEA 2000 network before, but now we can see WHY it was developed. Using a backbone design and using Tees to connect devices to the network, the network topology is really simple. You can tee in up to 50 devices on one NMEA 2000 backbone. We will have 13 devices total, so we are nowhere near capacity of this network. We are learning a lot and it is exciting to be setting up and installing all this new gear. Again, thanks goes to Colin Mack of Mack Sails. We bought everything from him and we would do it again in a heartbeat.  He is so great to deal with and he is very helpful.  Take a look at some of their work here www, Thank you, Colin!

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9 Replies to “NAC-3 B&G Autopilot Computer Installed”

  1. When I went into the locker I was usually by myself and to get in there I had to twist this way, then move this leg that way, then turn slightly and shimmy down before getting my other shoulder inside……

    I used to worry that I would not remember how to get out of there and no one would be around to dump a bucket of grease on me so I could slide out. 🙂

  2. Great work. Really informative. Did anyone need to go up the mast? Was the mast up when you ran the rope for the wire? Drew was in the locker with yoga poses for 2 weeks installing a Garmin 547 xs and connecting to a new computer and installing new software (wouldn't take the old). Installed NMEA 0183 from Garmin to autopilot computer. A separate NMEA 0183 to new laptop PC touchscreen Lenovo. We couldn't get a replacement Toughbook. Our Toughbook was 12 years old – it was time. Old GPS was 1999.
    You did it in good time; much faster.
    Deb and Drew

  3. Can you tell me gauges of wire you used? Also I believe the NEMA 2000 back bone needs to be electrified too. Did you encounter this? Photos really help. Thank you!

  4. Thanks for this post. We are about to embark on installing our new system. What size wiring did you use for the NAC to the battery. Difficult to find this information anywhere. Thanks Cara. SV Taurus NZ

    1. Hi Cara,

      I’m wondering if you ever determined the proper wire size? I’m having the same difficulty finding info and to call Navico is fruitless as you’re placed on hold and nobody ever picks up!


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