GNX
™
20/21 Installation Instructions
To obtain the best possible performance, install this marine
instrument according to these instructions. If you experience
difficulty during the installation, contact Garmin
®
Support, or seek
the advice of a professional installer.
This instrument communicates with NMEA 2000
®
sensors and
devices, and shows information such as speed, heading, and
water depth when connected to the appropriate sensors. The
instrument can also communicate with a NMEA
®
0183 device
using an optional data cable.
Important Safety Information
WARNING
See the
Important Safety and Product Information
guide in the
product box for product warnings and other important
information.
CAUTION
To avoid possible personal injury, always wear safety goggles,
ear protection, and a dust mask when drilling, cutting, or
sanding.
NOTICE
When drilling or cutting, always check what is on the opposite
side of the surface to avoid damaging the vessel.
Mounting Considerations
NOTICE
This device should be mounted in a location that is not exposed
to extreme temperatures or conditions. The temperature range
for this device is listed in the product specifications. Extended
exposure to temperatures exceeding the specified temperature
range, in storage or operating conditions, may cause device
failure. Extreme-temperature-induced damage and related
consequences are not covered by the warranty.
The mounting surface must be flat to avoid damaging the device
when it is mounted.
When selecting a mounting location, observe these
considerations.
• The mounting location should be at or below eye level to
provide optimal viewing as you operate your vessel.
• The mounting location should be at less than a 45° viewing
angle for the GNX 20 Marine Instrument with Standard LCD
and less than a 50° viewing angle for the GNX 21 Marine
Instrument with Inverted LCD. Screen color inversion occurs
when the viewing angle is greater than 30° in the 9 o'clock
direction on the GNX 20 and when the viewing angle is
greater than 60° in the 1 o'clock direction on the GNX 21.
• The mounting surface must be strong enough to support the
weight of the device and protect it from excessive vibration or
shock.
• To avoid interference with a magnetic compass, the device
should not be installed closer to a compass than the
compass-safe distance value listed in the product
specifications.
• The area behind the mounting surface must allow room for
the routing and connection of the cables.
Mounting the Device
NOTICE
If you are mounting the device in fiberglass, when drilling the
pilot holes, use a countersink bit to drill a clearance counterbore
through only the top gel-coat layer. This will help to avoid
cracking in the gel-coat layer when the screws are tightened.
The included template and hardware can be used to flush mount
the device in your dashboard.
1
Trim the flush-mount template and ensure it fits in the
location where you plan to mount the marine instrument.
The flush-mount template is included in the product box.
2
Remove the liner from the adhesive on the back of the
template and adhere it to the location where you plan to
mount the marine instrument.
3
If you plan to cut the hole using a rotary tool instead of a
90 mm (3.5 in.) hole saw, use a 10 mm (
3
/
8
in.) drill bit to drill
a pilot hole to begin cutting the mounting surface.
4
Using the 90 mm (3.5 in.) hole saw or rotary tool, cut the
mounting surface along the inside of the dashed line
indicated on the flush-mount template.
5
If necessary, use a file and sandpaper to refine the size of
the hole.
6
Place the marine instrument into the cutout to confirm that
the mounting holes on the template are in the correct
locations.
7
If the mounting holes are not correct, mark the correct
locations of the mounting holes.
8
Remove the marine instrument from the cutout.
9
Drill the 2.8 mm (
7
/
64
in.) pilot holes.
If you are mounting the marine instrument in fiberglass, use a
countersink bit as advised in the notice.
10
Remove the remainder of the template.
11
Place the included gasket on the back of the device and
apply marine sealant around the gasket to prevent leakage
behind the dashboard.
12
If you will not have access to the back of the device after you
mount it, connect all necessary cables to the device before
placing it into the cutout.
NOTE:
To prevent corrosion of the metal contacts, cover
unused connectors with the attached weather caps.
13
Place the marine instrument into the cutout.
14
Securely fasten the marine instrument to the mounting
surface using the supplied screws.
If you are mounting the marine instrument in fiberglass, use a
anti-galling lubricant as advised in the notice.
15
Snap the bezel into place.
GUID-E313CF8B-397D-48AF-8839-977C29E188D5 v4
August 2020
