Displaying Sonar on a portable Chartplotter (276c, 376c, 378 or 478)

To display a Sonar image on a portable marine chartplotter (GPSMAP 276c, 376c, 378, or 478), you will need to purchase and connect two items. The first item is a remote sounder box. You can use either of the two discontinued sounder boxes, the GSD 20 or GSD 21.

The second item you will need is a transducer. To find a compatible transducer, please visit the webpage for the remote sounder box that will be connected to the portable marine chartplotter. From this webpage, click on the Accessories tab and then choose Transducers.

The Installation Manual for the remote sounder box will provide a diagram that shows how to connect the portable chartplotter to the sounder box. The transducer will then plug directly into the sounder box.

Once everything is connected correctly, you will need to change a setting in the portable chartplotter. Please follow these directions to change this setting:

1. With the device powered ON, press the Menu button twice
2. Highlight the Setup tab on the left hand side of the screen
   1. If the Setup tab is not visible, keep scrolling down until it appears
3. Press the Right arrow button a few times to highlight the Interface tab at the top of the screen
   1. If the Interface tab is not visible, keeps scrolling right until it appears
4. Highlight the setting called Serial Data Format
5. Press the Enter button
6. Highlight Garmin Remote Sonar
7. Press the Enter button

Once all of the above steps are done, the device should now be able to display a Sonar image.