Fish finders from Lowrance, Simrad and B&G can record everything they show into a sonar log on their memory card. Looking at it again later usually takes the unit itself or Windows software. This tool opens the log in any browser, on a Mac, a PC, a tablet or a phone, and turns it into pictures and files you can keep, share and put on a map.
What it reads
- .sl2 logs, written by most Lowrance, Simrad and B&G units.
- .sl3 logs of newer units, also when they hold 3D sonar data (the 3D data itself isn't drawn).
- .slg logs of older Lowrance units.
The format is recognised by the content, not by the file name. Logs that end in the middle of a ping, as they do when the unit is switched off while logging, and logs with damaged stretches are read as far as they go; the result says what was skipped.
What you get
- Sonar pictures of every channel in the log: 2D sonar (and a second 2D channel if the unit logged two), down scan, and side scan with the left side on the left, the right side on the right and the boat's path down the middle. Each picture has a depth or range scale, time marks and the distance travelled, in amber, blue, greyscale or a light "paper" scheme for printing. Long logs are split into pictures of up to 2,400 pings; very long ones combine neighbouring pings, keeping the strongest echo, so a channel never needs more than 24 pictures.
- A GPX track with the depth, water temperature, speed and course at every point (about one point a second), for mapping apps and GPS software.
- A KML file for Google Earth with the track and the depth readings as coloured dots.
- A depth map: every depth reading drawn where it was taken, coloured from shallow to deep, with a depth scale, a scale bar and north.
- A CSV file with one row per ping: channel, frequency, time, latitude and longitude, depth, range, GPS speed, course, heading, water temperature and more.
- A summary: format, channels and frequencies, date and time, duration, distance, depth and temperature range, the area covered and any damaged parts.
Times, positions and units
Newer units store the date and time at the start of a log, in UTC (world time). The pictures, GPX and CSV use it; older logs and all .slg logs only count the time since logging started, so their marks read as minutes into the log. Positions are stored in Navico's own map projection and are converted to latitude and longitude. Units are chosen automatically: feet and miles for logs recorded in or near the United States, metres elsewhere; you can choose either.
Why the pictures can look different from the screen
A log keeps the echoes the unit received, not the screen. The colours come from the scheme you pick, and the automatic contrast spreads each channel's echo strengths over the whole colour scale so faint fish and structure show. Choose As recorded under More options for the values exactly as stored. The range is what the unit was set to while logging: a side scan logged at a short range shows only a narrow strip.
What it can't do
- Recordings of other brands, such as Humminbird (.DAT and .SON) or Garmin (.RSD).
- Draw the 3D sonar data of .sl3 logs.
- Draw depth contours: one track rarely covers an area densely enough for honest contours. The GPX and CSV carry every depth with its position for mapping software.
Privacy
The upload is deleted as soon as the log has been read, and the pictures and files are deleted automatically after 30 minutes. The files you download contain the positions and times of the log, so think about where you share them if a fishing spot is a secret.