Maritime navigation with a Rasp Pi and OpenCPN

Cast Off

After starting OpenCPN, you need to keep an eye out for a few issues. The first is that the current GPS position should appear at the bottom edge of the OpenCPN window. This means that the communication between OpenCPN and the GPS daemon is functioning properly. As soon as OpenCPN receives a GPS bearing, it will display a small boat icon at the corresponding coordinates on the map section of the window. The appearance of the boat signifies that the navigation system is now ready for operation.

Your DIY navigation device offers one additional advantage that is not always immediately apparent. Next to the location indicator at the bottom of the window, you will see a speed indicator to the right (Figure 3). The software calculates the current location of the boat by means of the changing GPS coordinates as the boat is underway. These are important pieces of information for small boats. In Germany, for instance, inland waterways have speed limits.

Figure 3: Live and in color: The combined GPS and OpenCPN system displays the current location and speed of the boat in the status bar at the bottom.

Captains of small boats often find it difficult to determine actual speed. Many boats have impeller logs at the bow, but these tend not to work in the summer. Mussels attach themselves and obstruct the wheels when boats stand stationary for long periods of time on the water. This problem is one of the reasons that having a GPS-based speedometer on board is a very good idea.

Expanded

A Rasp Pi used to build a maritime navigation system proves itself to be an extremely practical helper. The setup described here lends itself well to expansion. Thanks to OpenCPN, the Rasp Pi is also suitable for use as a source of NMEA 0183 signals [15], which make it possible for additional electronic equipment that might be on board to use the GPS data supplied by the Raspberry Pi. Boating enthusiasts in the OpenCPN forum [16] report successful trial runs in using the nanocomputer as a basis for automatic steering systems.

Using an NMEA 2000 gateway, it is possible to use NMEA 0183 devices on the network, giving all NMEA-capable devices (e.g., radios) access to the GPS data generated with OpenCPN. All radios currently available have a distress button, so the crew can send an alarm report to other ships located in the area in the event of an accident. The location of the ship is part of the report that is sent. Only a few radios also offer their own GPS receiver, so the GPS data from OpenCPN can solve this problem.