Open up google earth and mark waypoints you wish to put into your fish finder/gps. When you are done marking

 

Click File -> Save as

 

Name the file something you will remember in a location you can find. Use the KML File extension

 

Open a browser and navigate to

 

http://www.gpsvisualizer.com/gpsbabel/

 

Set the input file as google earth

 

Set the output file as lowrance

 

Click the browse button and attach your kml file that you saved from google earth

Click convert

 

Look for the link to the file, this file will be named the same thing you named it in google earth. The difference is that it will have a  .usr file extension. Download the file and save to your computer.

 

Put the file onto a micro SD card

 

Plug micro SD into the lowrance

 

Import waypoints from card

 

Enjoy your pre mapped spots!

 

Thats awesome.

Youre welcome

Note that you can also go the other direction and take the file on the card off your boat, change it to a kml file and open it in google earth