I had heard you can record sonar logs and submit to be added to maps. I had tried submitting previously but there was a problem with the format. Just found out that Navionics now accepts multiple formats of sonar logs as contributions to SonarCharts™. This includes Humminbird (DAT and GPX on all models, ION and Onix compatible within summer), Lowrance (GPX), Raymarine (SDF, GPX, NMEA),Simrad (GPX), and Garmin (ADM).