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Garmin 178C Review

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

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 youÂ’d 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.


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 can be saved at the boat’s position by pressing and holding the enter/mark key. This brings up a data box with waypoint information that includes a symbol, up to 68 are selectable, a name up to a 10-characters long, a 20-character comment line, lat/long, and a few other tidbits concerning the waypoint. Any of the information can be modified.

To change a waypoint name you’ll need to scroll through numbers and letters, a slow and tedious process but a common method in machines of this size and expense. Symbols are chosen from a table onscreen.


Route entry can be accomplished using a text listing of waypoints or by selecting points on the map page. We used the map method to enter our test route. Once a new route is selected via the main menu route tab the cursor and zoom function are used to choose and compile a list of points that make up the route. Each time the cursor is placed and the enter key is pressed twice the unit makes a new waypoint and places it in order in the route list.

Odds and Ends

Other features exist in this Garmin chartplotter bag of tricks, some good and some just OK.

The 178C can be set to north up or course up for the map page orientation, both worked well in our tests.

The unit course predictor displays as a thin line. It can be somewhat hard to see on a fully detailed map page.

Garmin’s man overboard function is activated by pressing the mob key. The machine then asks whether you want to navigate to the mob position. If you hit yes it changes to a map page offering little useful data on which to navigate precisely back the mob position (unless you have the data blocks on the map page turned on). To overcome this we simply pressed the page button and got the needed info on another page.

A number of different pages are displayed by pressing the page button. Additional options for the currently displayed page can be selected by hitting the menu key once. This brings up page specific data. Some pages on the Garmin can be displayed in vertical or horizontal windows that are user adjustable in size.


The 500-watt sounder integral to the 178C includes a dual frequency transducer (50/200 kHz). The list of features is long and includes auto and manual depth ranging, zoom, bottom lock, monochrome A-scope (flasher in Garmin parlance), and water temperature display.

What makes the sounder really standout is active cursor control of a whole slew of desirable functions. If you need to adjust the gain for a specific target all you need to do is use the right/left arrows on the cursor to select gain then press the up/down cursor to increase of decrease the gain as needed.

A total of 9 functions are available with the active cursor with gain, zoom, depth range, and frequency among the most useful.

We rate the Garmin 178C sounder good for presentation and excellent for ease of use.

Final Thoughts

The Garmin 178C has gobs of functionality, good screen resolution, and a simple to use sounder all in compact unit that is easy to wire and install.

You may still be able to find this discontinued sounder at a few marine stores, otherwise try Ebay. Either way you should find it available for a steal at around $500. It has a warranty period of 1-year on parts and labor.