You can just yet convert contour lines to routes (Navico units):
- RM: only export contour lines to a user map
- select the line(s) of the esired depth in RM, delete all others
- export as kmz-file
- load this kmz-file in GE and save again as kml-file
- convert the kml-file to a gpx-file (GPSBabel)
- convert this gpx-file in a "GPX Route"-file (
www.gpsies.com), use/try the settings!
- load/import into your unit (Repeat for the next other depth line. Or try all in one file?)
(note: if you have divided lines, you can use a GIS application for merging this lines)