Open a .sl2 sonar file:

Info: This tool converts Lowrance's chart plotter down-scan sonar files into a csv or kml file. It runs entirely in your web browser and does not send any data to a server. Because of this, it also works offline in modern browsers. Please note that your sl2 file must be smaller than your computer's available memory for a full conversion! - Use the ruby implementation if this is not the case.

Longitude conversion fixed thanks to examples from sl2decode.rb from Criss76 on Github!

[Source Code]