GPSMAP® 178C Sounder

Part Number: 010-00340-00


Own the lake with the GPSMAP 178C Sounder and its counterpart, the GPSMAP 172C. With a built-in sounder and worldwide marine basemap, the 178C is ready to handle all your fishing adventures.

Chart Your Course

The GPSMAP 178C features a built-in worldwide marine basemap and accepts BlueChart® offshore marine cartography, featuring detailed depth contours, inter-tidal zones, wrecks, navaids, and many other points of interest. For small-water anglers, the 178C is compatible with MapSource Recreational Lakes with Fishing Hot Spots, featuring fishing areas, boat ramps, marinas, and hazards for hundreds of popular U.S. and Canadian lakes. You can use compatible preprogrammed data cards, which insert easily into the slot on the front of the plotter.

Catch Some Fish

The 178C comes with a built-in sounder with Garmin’s exclusive See-Thru® fish targeting technology. The sounder features adjustable range, gain, zoom and bottom lock. It also has new digital display technology that offers an easy-to-read, semi-transparent digital readout so you can see sonar images "behind" the data.

GPSMAP 178C Sounder: Leaves fish with nowhere to hide

WAAS enabled BlueChart compatible Marine Updater


PDF Download detailed specs

Physical & Performance

Physical dimensions 6.3" x 4.9" x 2.8" (16.0 x 12.5 x 7.1 cm)
Display size, WxH 3.2" x 3.2" (8.1 x 8.1 cm)
Display resolution, WxH 320 x 320 pixels
Display type 256-color CSTN
Weight 1.2 lb (553 g)
Water rating IPX7
Antenna Internal with external connection
NMEA 0183 compatible
Power consumption 8 watts max at 13.8 vDC
Mounting options Bail with Swivel or Flush
Garmin Marine Network™ ports None

Maps & Memory

Accepts data cards 1 Garmin Data Card
Waypoints 3,000
Routes 50
Track log 10,000 trackpoints

Chartplotter Features

Garmin Sonar compatible
Supports DSC (displays position data from DSC-capable VHF radio)
Tide tables

Sonar Features & Specifications

Dual-frequency (50/200 kHz) sonar capable
Frequencies supported 50/200 kHz
Transmit power 500 W (RMS), 4,000 W (peak to peak)
Maximum depth 900 ft
Bottom lock (shows return from the bottom up)
Water temperature log and graph


NMEA 0183 input ports 2
NMEA 0183 output ports 2
Video input ports None
Video output ports None

In the Box

  • GPSMAP 178C Sounder
  • Basemap: Worldwide Marine
  • Internal or external antenna
  • Transom-mount transducer (optional)
  • Swivel mount bracket
  • Protective front cover
  • Power/data cable
  • Owner's manual
  • Quick reference guide


Maps for New Regions

Need maps for other regions? See all maps that are compatible with this device.

Need a map update?

Update the maps that came with your device for the best navigation experience.

Check for Updates