Garmin GNX 20 Marine instrument Installation Instruction

To obtain the best possible performance, install this marine 

instrument according to these instructions. If you experience 

difficulty during the installation, contact Garmin

®

 Product 

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.

See the Important Safety and Product Information guide in the 

product box for product warnings and other important 

information.

Always wear safety goggles, ear protection, and a dust mask 

when drilling, cutting, or sanding.

When drilling or cutting, always check what is on the opposite 

side of the surface.

Help us better support you by completing our online registration 

today.
• Go to 

.

• Keep the original sales receipt, or a photocopy, in a safe 

place.

• Go to 

for in-country support information.

• In the USA, call (913) 397.8200 or (800) 800.1020.
• In the UK, call 0808 2380000.
• In Europe, call +44 (0) 870.8501241.

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.

Using the included hardware and template, you can flush mount 

the device in the dashboard. If you want to mount the device 

using an alternative method where it appears flat with the front 

of the dashboard, you must purchase a flat-mount kit 

(professional installation recommended) from your Garmin 

dealer.
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 location should allow easy access to the keys 

on the device.

• 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.

If you are mounting the device in fiberglass, when drilling the 

four pilot holes, it is recommended to use a countersink bit to 

drill a clearance counterbore through only the top gel-coat layer. 

This will help to avoid any cracking in the gel-coat layer when 

the screws are tightened.
Stainless-steel screws may bind when screwed into fiberglass 

and overtightened. Garmin recommends applying an anti-seize 

lubricant to the screws before installing them.

The included template and hardware can be used to flush 

mount the device in your dashboard. To mount the device so 

the screen is flat with the dashboard, you must purchase a flat-

mount kit from your Garmin dealer.

Trim the flush-mount template and ensure it will fit in the 

location where you plan to mount the marine instrument.
The flush-mount template is included in the product box.

Remove the liner from the adhesive on the back of the 

template and apply it to the location where you plan to mount 

the marine instrument.

If you plan to cut the hole with a jigsaw 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.

Using the jigsaw or the 90 mm (3.5 in.) hole saw, cut the 

mounting surface along the inside of the dashed line 

indicated on the flush-mount template.

If necessary, use a file and sandpaper to refine the size of 

the hole.

Place the marine instrument into the cutout to confirm that 

the mounting holes on the template are in the correct 

locations.

If the mounting holes are not correct, mark the correct 

locations of the mounting holes.

Remove the marine instrument from the cutout.

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.

Remove the remainder of the template.

Place the included gasket on the back of the device and 

apply marine sealant around the gasket to prevent leakage 

behind the dashboard.

January 2014

190-01659-02_0A

Printed in Taiwan