The compact Garmin 178C we tested was equipped with an internal GPS antenna, an integral sounder, and a dual-frequency transducer. Other models of this Garmin chartplotter are available with an external GPS antenna and single frequency transducer.
The unit contains an internal world map and uses Garmin BlueChart cartography to enhance map details in the specific area covered by the card you choose.

Garmin 178C
The case is just over 6-inches wide and a tad under 5-inches high with a depth less than 3-inches.
All wiring for power, interface, and transducer leads connect to the back of the unit through a single multi-pin twist-lock connector. The transducer branch connects to the transducer with another twist-lock connector.
For us, wiring the Garmin 178C was simply a matter of connecting the power wires to the source and installing and connecting the transducer.
If you were planning to interface the 178C to another NMEA capable unit like an autopilot youd have to make several connections with some very small wires. Overall installation of the 178C was easy.
Screen Size and Viewability
The Garmin 178C screen has equal height and width measurements of 3.3-inches equating to a diagonal measurement of 4.5-inches. It carries a resolution of 320 x 320 pixels. Thirteen levels of control are available for screen brightness and contrast. We found the brightness control range to be adequate and the contrast control effective. Two color palettes, sun or dark, can be selected from the map tab on the main menu.
In daylight conditions, we found the 178C easy to see, though some reflectivity was noted. It showed almost no screen darkening when the tester wore polarized sunglasses. Overall we’d rate the screen good for daytime and nighttime viewability. Pushbuttons and the cursor pad are backlit.
Noted Screen Issue
The screen does have an occasional problem with overheating when it is exposed to long periods of direct sunlight. Once the overheating starts the screen begins to lighten and finally blank. Cooling the unit off by putting it in the shade resolves the issue.
Operation
Most functions on the 178C are manipulated through multi-layered menus. Hitting the menu key twice brings up the main menu with a long list of items in tabular format on the left side of the screen, selecting a tab opens another menu page where you can make and execute selections.
Waypoints
Waypoints can





