I am running linux and use GpsBabel
to convert tracks, routes, waypoints from GPX to KML. Export from OpenCPN as GPX file and run GpsBabel from the command line. Lots of formats, simple command line.
Don't know what flavor of linux you are running, but you might want to check out Navigatrix
. Full operating system you can run from a 4 gig stick. Designed by cruisers for cruisers... Includes OpenCPN, Airmail, Tide Charts
, Grib Imports, Celestial Nav tables and reduction, Wine (to run window$ applications) and a bunch more. You can run side by side with your current
OS as a dual boot or off the stick. Oh, and it includes GpsBabel already... (German Language version available as well)
Hope it's a help