My antiquated knotmeter is out of commission due to a broken transducer. I’ll keep looking for a replacement but in the meantime I decided on simplicity and will monitor speed using a handheld GPS, the Garmin GPSMAP 78sc. I also want to have the ability to forego simplicity and connect the handheld to my PC running OpenCPN, an open source chart plotting application. It took a little fiddling to get the PC to pull in position data from the Garmin. But it’s easy to set up and step by step instructions are provided below.
These are the setup steps for connecting the Garmin GPSMAP 78sc handheld GPS to a PC running Windows 7 64 bit using a standard USB cable. My version of OpenCPN is 3.2.2 and the PC is a Dell XPS M1330 laptop.
On the Garmin GPS, navigate to: Setup > System > Interface. Select: Garmin Spanner.
On the PC, install OpenCPN.
On the PC, install Garmin USB drivers. The drivers are available for download as a simple executable from the Garmin website:
USB Drivers software version 2.3.1
In OpenCPN, open the tools dialog. Click the Connections tab. Click Add Connections. In the Properties section, select:
Click the Apply button.
Connect the GPS to the PC using the included USB cable. The GPS will prompt: Would you like to go to Mass Storage? Select No.
That’s it. Position information should now be flowing into the OpenCPN software. You can check this by opening the NMEA Debug Window in OpenCPN. Do this by navigating to Connection properties again and checking the check box. You should see new lines of text appearing in the debug window every second.