File format Geonav 4c?

I'd like to download tracks from my Geonav 4c GPS and plot them on my
PC using OziExplorer. Also the other way around: make waypoints on Ozi
and upload them to the Geonav. Unfortunately Geonav uses some strange
file format, both for tracks and for routes.

Can anybody help me eg by providing the file formats or with the name
of an utility that I can use for this?

Thx / Aad