From Bassboatcentral, hope they don't mind sharing.
How to convert Humminbird Waypoints and Trails to Lowrance.. 7:29 AM 2/3/2012 Reply Edit
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Using GPS Babel to convert Humminbird waypoints to Lowrance format
Free download at
http://www.gpsbabel.org/First download your waypoints from your Humminbird locator onto an Sd card. Note that Humminbird uses different files for waypoints and routes (.hwr) and tracks (.ht) You can convert both. Lowrance uses a common .usr file for waypoints, routes, and tracks.
Next download a free conversion program called GPSBabel (GPSBabel Download).
Humminbird to Lowrance Conversion
Launch the GPSBabel program and select Humminbird Waypoints as the input. Browse to your waypoint file and select it.
Select Lowrance USR as your output file and provide a name for the new Lowrance .usr file to be created.
Select Apply and the program will convert the waypoints and place the newly formatted output file in the destination you chose.
Copy the new Lowrance .usr file onto an Sd card and upload it into your Lowrance Unit.