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Autopilot

Beta

Autopilot is a beta feature and stays hidden until you turn on Beta Options: on mobile in Settings › Advanced & Development, on desktop in Settings › General › Advanced. Turning Beta Options off again stops any navigation in progress.

Bristol Maps can steer your autopilot along a go-to waypoint or a saved route. It works out the cross-track error, bearing and distance to the next waypoint once a second, advances through the route leg by leg, and sends standard NMEA 0183 steering sentences to the autopilot.

Navigation aid only

The skipper remains responsible for a proper lookout and safe navigation at all times. Check that every leg of the route clears hazards, because the autopilot steers straight along each leg. Test at low speed in open water before you rely on it, and be ready to steer by hand.

What you need

  • An autopilot that accepts NMEA 0183 navigation input (APB / RMB / XTE), or an NMEA 2000 autopilot behind a gateway that converts them.
  • A two-way link from Bristol Maps to that input:
    • Yacht Devices YDWG-02 (Wi-Fi) or YDEN-02 (Ethernet) gateway on the boat’s NMEA 2000 network. The gateway turns APB / RMB / XTE into PGNs 129283 (cross-track error), 129284 (navigation data) and 129285 (route / waypoint information).
    • Or an NMEA 0183 multiplexer with a network or USB input that is routed to the autopilot.
    • Desktop only: a USB-to-NMEA 0183 (RS-422) adapter wired to the autopilot’s NMEA input, added as a serial connection (usually 4800 baud).

Yacht Devices gateway setup

Menu names vary by firmware; the gateway’s manual has the exact screens.

  1. Open the gateway’s web page and find the server Bristol Maps connects to (for example TCP port 1456).
  2. Set that server to NMEA 0183 and to both send and receive (bidirectional), so it accepts sentences from Bristol Maps as well as sending its own.
  3. In the gateway’s NMEA 0183 → NMEA 2000 conversion settings, make sure APB, RMB and XTE are converted. Save, and restart the gateway if it asks.
  4. Add the gateway in Bristol Maps as an NMEA connection (mobile: Settings › NMEA & Instruments; desktop: Settings › Devices & Connections) and confirm it connects.

Turning on autopilot output

  1. Open Settings › Autopilot.
  2. Turn on Send steering to autopilot and read the safety notice (shown once).
  3. Pick the gateway under Send to connection.
  4. Optional: Also send to Wi-Fi GPS clients adds the sentences to the Share my GPS over Wi-Fi server on port 10110, for a multiplexer or plotter that relays them.
  1. Open Settings › Devices & Connections › Autopilot Output.
  2. Tick Send steering to autopilot and accept the safety notice (shown once).
  3. Pick the gateway or serial connection under Connection.

Talker ID is GP by default, which most autopilots accept. Change it to EC (electronic chart) or II if your autopilot only listens to that talker.

Going to a waypoint or following a route

  • Settings › Autopilot → Go To Waypoint lists your waypoints, nearest first.
  • Settings › Autopilot → Follow Route, or Follow on a route’s edit page.
  • Data › Autopilot…, then pick a waypoint or a route.
  • Or right-click a waypoint on the chart (Go To with Autopilot…) or a route (Follow with Autopilot…).

When you start a route you choose Start at first waypoint, Join nearest leg (for a route you are already part-way along) or Reverse route. The first leg always runs from where the boat is now to the first waypoint, so the autopilot is never asked to swing back onto a line you are far off.

The Autopilot screen shows the leg (START → Egegik Bar), the cross-track error with the side to steer, the bearing (°T) and the distance to the waypoint, and where the output is going. Use Next / Previous to skip or go back a waypoint, and Stop to end navigation.

On the chart, the active leg is drawn as a solid magenta line, the rest of the route dashed, and the waypoint you are heading for with its arrival circle and name.

A leg is complete when the boat enters the arrival circle (0.05 NM) or crosses the line through the waypoint at right angles to the leg (perpendicular passed), so a boat that is pushed wide still moves on to the next leg. After the last waypoint, navigation ends.

Once navigation is running, engage your autopilot’s track / nav / route mode (the name depends on the make). Bristol Maps does not switch the autopilot into or out of track mode.

What is sent

Once a second while navigating:

Sentence Contents
APB Cross-track error and steer direction, arrival circle / perpendicular flags, bearing origin → destination, bearing and heading-to-steer to the destination, destination ID
RMB Cross-track error, origin and destination IDs, destination position, range, bearing, closing speed, arrival flag
XTE Cross-track error and steer direction
BWC Great-circle bearing and distance to the waypoint, its position and ID
BOD Bearing from the leg’s origin to its destination

Bearings are true. Magnetic fields are left empty because the app has no magnetic variation source; autopilots that need magnetic apply their own variation. Waypoint names are shortened to 8 characters with NMEA-reserved characters removed.

When output stops

Output sends one set of sentences marked void (status V) and then goes silent when:

  • the GPS fix is lost or more than 10 seconds old,
  • the last waypoint is reached, or you tap Stop,
  • autopilot output is turned off,
  • the app is closed, or (mobile) sent to the background with Keep steering in the background turned off.

Your autopilot should alarm and leave track mode. When the fix comes back while you are still navigating, output resumes; re-engage track mode on the autopilot yourself. Navigation is not remembered across app restarts.

Steering with the screen locked (mobile)

Keep steering in the background (on by default) keeps the gateway connection and GPS running when the screen locks or you switch to another app, so steering carries on. On Android a notification, “Autopilot steering active”, shows while it runs.

  • It uses more battery. Keep the phone or tablet on charge.
  • The phone can still stop the app (very low battery, the system closing apps, a restart). Your autopilot then sees the data stop and should alarm, but it will not get a void sentence first.
  • If the background GPS gets no fix for 5 minutes, Bristol Maps gives up and releases the gateway connection. Open the app to resume.
  • Turn the setting off if you want output to go void whenever the app leaves the screen.

Garmin Reactor autopilots

Garmin autopilots on NMEA 2000 steer a route from the standard navigation PGNs 129283 and 129284, which a Yacht Devices gateway produces from Bristol Maps’ APB, RMB and XTE. A few things specific to Garmin:

  • Engage it on the Garmin helm control. Garmin uses its own, undocumented messages to change autopilot mode, so Bristol Maps cannot switch a Reactor into or out of route mode. Start navigation in Bristol Maps first, then choose the route / “Route To” mode on the GHC helm control (or a Garmin chartplotter).
  • Only one navigation source. If a Garmin chartplotter is also on the network, make sure it is not navigating to a waypoint or route of its own, or the autopilot may follow it instead.
  • When Bristol Maps stops or loses its fix, the autopilot loses navigation data and should alarm. Check in the dockside test below what yours does next (for example, whether it drops to heading hold or standby).

Garmin does not publish whether a given Reactor model and software version accepts navigation data from a non-Garmin source, so do the dockside check before relying on it.

Recording what your helm control sends

Bristol Maps can’t switch an autopilot’s mode yet. To help add it for Garmin autopilots, you can record the NMEA 2000 messages a Garmin GHC (or any helm control) sends when you press its buttons and share the file with Bristol Maps support. Bristol Maps only listens while recording. The one exception is Identify devices, which sends the standard NMEA 2000 requests asking each device for its name and model.

  1. On the Yacht Devices gateway, set a second server to the RAW protocol (for example TCP port 1457), and add it as an NMEA connection. Keep your normal NMEA 0183 connection for steering.
  2. Open the capture screen: mobile Settings › Autopilot › Capture Helm Control Messages, desktop Data › Autopilot… › Capture Helm Control Messages…. Pick the RAW connection and start the capture.
  3. Tap Identify devices once.
  4. Press a button on the GHC, then tap the same button in Bristol Maps within a second. Do each button (Engage, Standby, Heading Hold, Route To, the course-change buttons) a few times, a few seconds apart. Use Other button for anything else.
  5. Stop the capture and share (mobile) or save (desktop) the file.

Do this tied up with the steering clear, or in open water: the autopilot really engages when you press its buttons. The file lists the devices on the network, what each sent in the 4 seconds after each button mark (messages that only appear after marks are starred), and the full log.

Checking it before you leave the dock

Most autopilots and the Yacht Devices gateway can be checked without moving the boat:

  1. Put the autopilot in standby or its simulator / demo mode (see its manual).
  2. Start a go-to to a waypoint a few miles off.
  3. On the autopilot or a plotter’s data page, check that the waypoint name, bearing, distance and cross-track error match the Bristol Maps Autopilot screen. The Yacht Devices web page can also show the incoming sentences and the PGNs it sends.
  4. Tap Stop and check that the autopilot shows a navigation-data-lost alarm.

Then, in open water at low speed, engage track mode on a short go-to and watch the first turn.