Garmin GT20-TM, GT21-TM Installation Instructions
DownVü Transducer Installation
Instructions
To obtain the best performance and to avoid damage to your
boat, install the Garmin® DownVü transducer according to these
instructions.
Read all installation instructions before proceeding with the
installation. If you experience difficulty during the installation,
contact Garmin Product Support.
Registering Your Device
Help us better support you by completing our online registration
today.
• Go to http://my.garmin.com.
• Keep the original sales receipt, or a photocopy, in a safe
place.
Contacting Garmin Product Support
• Go to www.garmin.com/support and click Contact Support
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.
Updating the Device Software
Before you can update the software, you must obtain a
software-update memory card or load the latest software onto a
memory card.
Turn on the chartplotter.
1
After the home screen appears, insert the memory card into
2
the card slot.
NOTE: In order for the software update instructions to
appear, the device must be fully booted before the card is
inserted.
Follow the on-screen instructions.
3
Wait several minutes while the software update process
4
completes.
The device returns to normal operation after the software
update process is complete.
Remove the memory card.
5
NOTE: If the memory card is removed before the device
restarts fully, the software update is not complete.
Tools Needed
• Drill and drill bits
• 7 mm wrench
• 3 mm hex wrench
• Number 2 Phillips screwdriver
• Masking tape
• Marine sealant
Important Safety Information
WARNING
See the Important Safety and Product Information guide in the
product box for product warnings and other important
information.
You are responsible for the safe and prudent operation of your
vessel. Sonar is a tool that will enhance your awareness of the
water beneath your boat. It does not relieve you of the
responsibility of observing the water around your boat as you
navigate.
CAUTION
Failure to install and maintain this equipment in accordance with
these instructions could result in damage or 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.
Loading the New Software on a Memory Card
You must copy the software update to a memory card.
Insert a memory card into the card slot on the computer.
1
Go to www.garmin.com/support/software/marine.html.
2
Select Download next to “Garmin Marine Network with SD
3
card”.
Read and agree to the terms.
4
Select Download.
5
If necessary, select Run or save and open the file.
6
If necessary, select the drive associated with the memory
7
card, and select Next > Finish.
About the Transducer
The transducer transmits and receives sound waves through
the water, and relays sound-wave information to your Garmin
sonar device.
Assembling the Transducer
Secure the mount À to the transducer Á with the included
1
8 mm M4 screws Â, 4 mm flat washers Ã, and M4 split
washers Ä.
February 2014
190-01682-02_0A Printed in Taiwan
Secure the mount to the bracket Å with the included 12 mm
2
M4 screws Æ, M4 flat washers Ç, and M4 lock nuts È.
NOTE: You can use the 7 mm wrench to hold the lock nut in
place while you tighten each 12 mm M4 screw.
Installing the Transducer on a Transom
Mounting Location Considerations
• The transducer should be mounted as close to the center of
the boat as possible.
• The transducer should not be mounted behind strakes,
struts, fittings, water intake or discharge ports, or anything
that creates air bubbles or causes the water to become
turbulent.
The transducer must be in clean (non-turbulent) water for
optimal performance.
• The transducer should not be mounted in a location where it
might be jarred when launching, hauling, or storing.
• On single-drive boats, the transducer must not be mounted
in the path of the propeller.
The transducer can cause cavitation that can degrade the
performance of the boat and damage the propeller.
• On twin-drive boats, the transducer should be mounted
between the drives, if possible.
Installing the Transom-Mount Hardware
NOTICE
If you are mounting the bracket on fiberglass with screws, 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.
Do not cut the transducer cable. Cutting the transducer cable
will void your warranty.
Position the transducer mount À at the mounting location on
1
the transom.
Using the 4 mm (5/32 in.) bit, drill the pilot holes
5
approximately 15 mm (19/32 in.) deep at the marked
locations.
Apply marine sealant to the included 20 mm screws, and
6
loosely attach the transducer assembly to the transom.
Adjust the transducer assembly so it extends beyond the
7
bottom of the transom  approximately 3 mm (1/8 in.) on
fiberglass hulls or 10 mm (3/8 in.) on aluminum hulls.
Make sure the transducer is aligned parallel to the water line.
8
If you need to route the cable through the transom, choose a
9
pilot-hole location well above the waterline à and mark it.
Place a cable clamp on the transducer cable Ä,
10
approximately one third of the distance between the
transducer and the top of the transom or the pilot hole.
Mark the pilot-hole location for the cable clamp, and using a
11
3.2 mm (1/8 in.) bit, drill a pilot hole approximately 10 mm
(3/8 in.) deep.
Apply marine sealant to the included 12 mm screw, and
12
attach the cable clamp to the transom.
Repeat steps 10–12 to install the other cable clamp
13
approximately two thirds of the distance between the
transducer and the top of the transom or the pilot hole.
If you marked a pilot hole in step 9, choose the appropriate
14
drill bit to drill a pass-through hole completely through the
transom:
• If you have the 4-pin cable, use a 16 mm (5/8 in.) drill bit.
• If you have the 8-pin cable, use a 25 mm (1 in.) drill bit.
Route the transducer cable to the sounder:
15
• If you are routing the cable using a pass-through hole,
feed it through the hole you drilled in step 14, and install
the cable-entry cover Ã.
• If you are not routing the cable using a pass-through hole,
route the cable up and over the top of the transom Å.
Avoid routing the cable close to electrical wires or other
sources of electrical interference.
Installing the Cable-Entry Cover
If you routed the cable through the transom after you installed
the transducer, you should install the cable-entry cover to keep
water from entering your boat.
Place the cable-entry cover À over the hole and the cable,
1
with the opening pointing downward, and mark the location
of the two pilot holes.
Align the transducer parallel to the water line Á, and mark
2
the center location of the two outer holes and a center hole
on the transducer mount.
Wrap a piece of tape around a 4 mm (5/32 in.) bit at 15 mm
3
(19/32 in.) from the point of the bit, to avoid drilling the pilot
holes too deep.
If you are installing the bracket on fiberglass, place a piece of
4
tape over the pilot-hole location to reduce cracking of the gelcoat.
2
Remove the cable-entry cover, and, using a 3.2 mm (1/8 in.)
2
bit, drill the pilot holes approximately 10 mm (3/8 in.) deep.
Fill the pass-through hole with marine sealant so it covers
3
the cable completely and there is excess sealant around the
hole and the cable.
Place the cable-entry cover over the hole and the cable, with
4
the opening pointing downward.
Apply marine sealant to the included 12 mm M4 screws, and
5
attach the cable-entry cover to the transom.
Wipe away all excess marine sealant.
6
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