Garmin GT20-TM Trolling Motor Mount Installation Instructions

: June 12, 2024
: Garmin

Table of Contents

Garmin GT20-TM Trolling Motor Mount
Important Safety Information
- Preparing the Transducer for Long-Term Exposure to Water
Installing the Transducer on a Transom
- Installing the Transom-Mount Hardware
Testing the Installation
Software Update
Registering Your Device
FREQUENTLY ASKED QUESTIONS
Read User Manual Online (PDF format)
Download This Manual (PDF format)

Garmin GT20-TM Trolling Motor Mount

Garmin-GT20-TM-Trolling-Motor-Mount-PRODUCT

Important Safety Information

WARNING

See the Important Safety and Product Information guide in the Chartplotter or Fishfinder 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 enhances 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. This equipment should be installed by a qualified marine installer. To obtain the best performance and avoid damage to your boat, you must install the Garmin® device according to these instructions. Read all installation instructions before proceeding with the installation. If you experience difficulty during the installation, contact Garmin Product Support.

Tools Needed

Drill and drill bits
Number 2 Phillips screwdriver
Masking tape
Marine sealant

Preparing the Transducer for Long-Term Exposure to Water

NOTICE

Do not use acetone or acetone-based products on the transducer. Acetone damages the plastic transducer housing.

When you install a transducer on a boat that spends a significant amount of time in the water, you should coat the transducer and mounting hardware with water-based anti-fouling paint to prevent marine growth.

Lightly sand the transducer and mounting hardware with a fine-grit abrasive pad.
Wipe the transducer and mounting hardware with isopropyl alcohol.
Apply water-based anti-fouling paint to the transducer and mounting hardware.

Mounting Consideration

To ensure peak performance with the lowest noise and interference, you should route the transducer cable away from ignition wires, house batteries, and wires, trolling motor batteries and wires, and high-energy wires such as radar, audio amplifier, and autopilot pump wires.

Installing the Transducer on a Transom

Mounting Location Considerations

The transducer should be mounted parallel to the water line.
The transducer should be mounted as close to the center of the boat as possible.
If your propeller moves clockwise when the boat moves, the transducer should be mounted on the starboard side.
If your propeller moves counter-clockwise when the boat moves, the transducer should be mounted on the port side.
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 boats with outboard or inboard/outboard motors, the transducer should be mounted at least 38 cm (15 in.) from the propeller.
On twin-drive boats, the transducer should be mounted between the drives, if possible.

Assembling the Transducer with a Transom Mount Bracket

Attach mount 1 to transducer 2 with the included star washers 3 , and screws 4.
Attach the mount to bracket 5 with bolt 6 , rubber washer 7 , flat washer 8 , and lock nut 9.

NOTE: The bolt should be tight enough to hold the transducer in place when the boat moves at high speed, but loose enough to allow the transducer to pivot out of the way if the transducer hits an obstruction.

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 cracking in the gel-coat layer when the screws are tightened.

The cables connected to the transducer should not be cut, because cutting the transducer cables voids your warranty.

Cut out the template.
With template 1 aligned vertically on the transom at the installation location (Mounting Consideration, page 1), place the bottom corner 2 of the template on the edge of the transom.
Mark the center location of the two holes of the template.
Remove the template from the transom.
Wrap a piece of tape around a 4 mm (5/32 in.) bit at 18 mm (7/10 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 tape over the pilot-hole location to reduce the cracking of the gel coat.
Using the 4 mm (5/32 in.) bit, drill the pilot holes approximately 18 mm (7/10 in.) deep at the marked locations.
Apply marine sealant to the included 20 mm screws, and
Route the cable under the transom mount cable hook.
If you must route the cable through the transom, choose a pilot-hole location well above the waterline and mark it.
Place a cable clamp on the transducer cable, approximately halfway between the transducer and the top of the transom or the pass-through pilot hole.
Mark the pilot-hole location for the cable clamp, and using a 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 attach the cable clamp to the transom.
If you marked a pilot hole in step 7, choose the appropriate 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:
If you are routing the cable using a pass-through hole, push it through the pass-through hole, and install the cable-entry cover (Installing the Cable-Entry Cover, page 2).
If you are not routing the cable using a pass-through hole, route the cable up and over the top of the transom.
You should 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 1 over the hole and the cable, with the opening pointing downward, and mark the location of the two pilot holes.
Remove the cable-entry cover, and, using a 3.2 mm (1/8 in.) bit, drill the pilot holes approximately 10 mm (3/8 in.) deep.
Fill the pass-through hole with a marine sealant so it covers 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 the opening pointing downward.
Apply marine sealant to the included 12 mm M4 screws, and attach the cable-entry cover to the transom.
Wipe away all excess marine sealant.

Testing the Installation

NOTICE

You should check your boat for leaks before you leave it in the water for an extended period of time.

Because water is necessary to carry the sonar signal, the transducer must be in the water to work properly. You cannot get a depth or distance reading when out of the water. When you place your boat in the water, check for leaks around any screw holes that were added below the water line.

Testing the Transom-Mount Transducer Installation

NOTICE

When adjusting the depth of the transducer, make the adjustments in small increments. Placing the transducer too deep can adversely affect the performance of the boat and put the transducer at risk of striking underwater objects.

Test the transom-mount transducer installation in open water free of obstacles. Pay attention to your surroundings as you test the transducer.

With the boat in the water, turn on the chart plotter.
Drive the boat at a slow speed. If the chartplotter appears to be working properly, gradually increase speed while observing the chart plotter.
If the sonar signal is suddenly lost or the bottom return is severely degraded, note the speed at which this occurs.
Return the boat to the speed at which the signal was lost, and make moderate turns in both directions while observing the chart plotter.
If the signal strength improves while turning, adjust the transducer so that it extends another 1/8 in. (3 mm) below the transom of the boat.
Repeat steps 2–4 until the degradation is eliminated.
If the signal does not improve, move the transducer to a different location on the transom, and repeat the test.

Installing the Transducer on a Trolling Motor

Assembling the Trolling Motor Mount

Using the 8 mm M4 screws 1 and 4 mm star washers 2 , attach the trolling motor mount 3 to the transducer 5.
Route the cable through cable exit 5 so the cable is on the top side of the trolling motor housing when stowed.

Installing the Transducer on a Trolling Motor

NOTICE

Do not cut the transducer cable. Cutting the transducer cable will void your warranty.

Insert the hose clamp 1 through the slot on the transducer mount 2 , until equal lengths extend on both sides of the mount.
Place the transducer mount against the body of the trolling motor with the narrow end of the transducer pointed away from the propeller.
Secure the hose clamp around the body of the trolling motor, and tighten the hose clamp.
Position the transducer so it is parallel to the bottom when in use.
Use the included cable ties to secure the transducer cable.
Route the transducer cable to the installation location of the sounder while taking these precautions.
- The cable should not be routed close to electrical wires or other sources of electrical interference.
- The cable must not be pinched when the trolling motor is deployed or stowed.

Software Update

You may need to update the device software when you install the device or add an accessory to the device.

Loading the New Software on a Memory Card

You must copy the software update to a memory card using a computer that is running Windows® software.

NOTE: You can contact Garmin customer support to order a preloaded software update card if you do not have a computer with Windows software.

Insert a memory card into the card slot on the computer.
Go to www.garmin.com/support/software/marine.html.
Select Download next to the software bundle that corresponds with your device.
Read and agree to the terms.
Select Download.
If necessary, select Run.
If necessary, select the drive associated with the memory card, and select Next > Finish.

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.
After the home screen appears, insert the memory card into 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.
Wait several minutes while the software update process completes.
When prompted, leave the memory card in place and restart the chartplotter manually.
Remove the memory card.
NOTE: If the memory card is removed before the device restarts fully, the software update is not complete.

Registering Your Device

Help us better support you by completing our online registration today.
Go to my.garmin.com.
Keep the original sales receipt, or a photocopy, in a safe place.

Contacting Garmin Product Support

Go to support.garmin.com for in-country support information.
In the USA, call 913-397-8200 or 1-800-800-1020.
In the UK, call 0808 238 0000.
In Europe, call +44 (0) 870 850 1241.

Garmin® and the Garmin logo are trademarks of Garmin Ltd. or its subsidiaries, registered in the USA and other countries. These trademarks may not be used without the express permission of Garmin.Windows® is a registered trademark of Microsoft Corporation in the United States and other countries.

FREQUENTLY ASKED QUESTIONS

What is the Garmin GT20-TM Trolling Motor Mount?

The Garmin GT20-TM Trolling Motor Mount is a transducer specifically designed for trolling motors. It combines a traditional 77/200 kHz HD-ID sonar with Garmin's CHIRP Down scanning sonar, providing clear and detailed fish arches and crisp target separation.

What type of transducer is the Garmin GT20-TM Trolling Motor Mount?

The Garmin GT20-TM Trolling Motor Mount is a transom-mounted transducer.

What frequencies does the Garmin GT20-TM Trolling Motor Mount operate on?

The Garmin GT20-TM Trolling Motor Mount operates at two frequencies: 77 kHz for traditional sonar and 200 kHz for Down scanning sonar.

What is the beam angle of the Garmin GT20-TM Trolling Motor Mount?

The beam angle of the Garmin GT20-TM Trolling Motor Mount is 45 degrees for the traditional sonar and 2D CHIRP, and 16 degrees for the Down scanning sonar.

What is the depth capability of the Garmin GT20-TM Trolling Motor Mount?

The Garmin GT20-TM Trolling Motor Mount has a maximum depth capability of approximately 1,900 feet in freshwater for the traditional sonar and approximately 750 feet for the Down scanning sonar.

Is the Garmin GT20-TM Trolling Motor Mount suitable for saltwater use?

Yes, the Garmin GT20-TM Trolling Motor Mount is designed for both freshwater and saltwater use, making it suitable for various fishing environments.

Can the Garmin GT20-TM Trolling Motor Mount be used with any trolling motor?

The Garmin GT20-TM Trolling Motor Mount is compatible with most trolling motors, but it's always recommended to check the compatibility with your specific trolling motor model before purchasing.

Does the Garmin GT20-TM Trolling Motor Mount come with a trolling motor mount bracket?

Yes, the Garmin GT20-TM Trolling Motor Mount comes with a trolling motor mount bracket that allows for easy installation on trolling motors.

Does the Garmin GT20-TM Trolling Motor Mount support DownScan Imaging?

No, the Garmin GT20-TM Trolling Motor Mount does not support DownScan Imaging. It provides Down scanning sonar instead.

What type of connector does the Garmin GT20-TM Trolling Motor Mount use?

The Garmin GT20-TM Trolling Motor Mount uses an 8-pin connector for easy installation and connection to compatible Garmin fishfinders.

Can the Garmin GT20-TM Trolling Motor Mount be used with other fishfinder brands?

The Garmin GT20-TM Trolling Motor Mount is specifically designed for Garmin fishfinders and is optimized for use with Garmin units. However, with the right adapters and compatibility, it may be possible to use them with other fishfinder brands.

Is the Garmin GT20-TM Trolling Motor Mount capable of temperature sensing?

Yes, the Garmin GT20-TM Trolling Motor Mount includes a built-in temperature sensor, allowing you to monitor the water temperature while you fish.

What is the cable length of the Garmin GT20-TM Trolling Motor Mount?

The cable length of the Garmin GT20-TM Trolling Motor Mount is approximately 20 feet, providing ample reach for installation and connection to your fishfinder unit.

Does the Garmin GT20-TM Trolling Motor Mount include a mounting hardware kit?

Yes, the Garmin GT20-TM Trolling Motor Mount comes with a mounting hardware kit that includes the necessary components for installation on your trolling motor.

Can the Garmin GT20-TM Trolling Motor Mount be adjusted for different depths and angles?

Yes, the Garmin GT20-TM Trolling Motor Mount is adjustable and can be positioned at various depths and angles to optimize the sonar performance and avoid interference with the trolling motor.

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