In Google Earth you can go to file / options and change how the coordinates are displayed with several options to choose. On you HDS you can go in and change how they are displayed and or entered in as well. Match the HDS to GE or match GE to the HDS by changing the options.
Match the coordinate formats. Set Google Earth and your Lowrance units to the same format if manually entering a few waypoints. For a large number of waypoints, save the waypoints from GE in KML or KMZ format, then use GpsBabel, Reefmaster or RideLeader to make a GPX file to import.
Waypoint and track-point coordinates are internally stored in HDS, Humminbird or Garmin units in digital format as that is what computers calculate. The different GPS formats you set are only for entering or displaying of those coordinates. Change the HDS coordinates display format and change the coordinate format back does not change the internal digital representation.