Garmin | GT15M-TM | Installation instructions | Garmin GT15M-TM Installation Instructions

Garmin GT15M-TM Installation Instructions
2 Wipe the transducer and mounting hardware with isopropyl
GT15M-TM Transom/
Trolling Motor Mount
3 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.
Assembling the Transducer
Attach the transducer À to the mount with the included lock
nut Á, rubber washer Â, metal washer Ã, and bolt Ä.
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.
Installation Instructions
Important Safety Information
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
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.
When drilling or cutting, always check what is on the opposite
side of the surface.
To obtain the best performance and to avoid damage to your
boat, you must install the Garmin device according to these
Read all installation instructions before proceeding with the
installation. If you experience difficulty during the installation,
contact Garmin Product Support.
Tools Needed
Drills and drill bits
Number 2 Phillips screwdriver
Masking tape
Marine sealant
Preparing the Transducer for Long-Term Exposure to
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 a water-based antifouling paint to prevent marine growth.
1 Lightly sand the transducer and mounting hardware with a
fine-grit abrasive pad.
January 2017
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.
Installing the Transom-Mount Hardware
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
Printed in Taiwan
The cables connected to the transducer should not be cut,
because cutting the transducer cables voids your warranty.
1 Cut out the template.
2 With the template À aligned vertically on the transom at the
installation location (Mounting Location Considerations,
page 1), place the bottom corner Á of the template on the
edge 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.
1 Place the cable-entry cover À over the hole and the cable,
with the opening pointing downward, and mark the location of
the two pilot holes.
3 Mark the center location of the two holes of the template.
4 Remove the template from the transom.
5 Wrap a piece of tape around a 4 mm (5/32 in.) bit at 18 mm
2 Remove the cable-entry cover, and, using a 3.2 mm (1/8 in.)
(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 cracking of the gel
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
attach the transducer assembly to the transom.
Route the cable under the transom mount cable hook.
bit, drill the pilot holes approximately 10 mm (3/8 in.) deep.
Fill the pass-through hole with 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.
Installing the Transducer on a Trolling Motor
Do not cut the transducer cable. Cutting the transducer cable
will void your warranty.
1 Insert a hose clamp À (not included) through the slot on the
transducer mount Á, until equal lengths extend on both sides
of the mount.
10 If you must route the cable through the transom, choose a
pilot-hole location well above the waterline and mark it.
11 Place a cable clamp on the transducer cable, approximately
halfway between the transducer and the top of the transom or
the pilot hole.
12 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.
13 Apply marine sealant to the included 12 mm screw, and
attach the cable clamp to the transom.
14 If you marked a pilot hole in step 3, using a 25 mm (1 in.) drill
bit, drill a pass-through hole completely through the transom.
15 Route the transducer cable to the sounder:
• If you are routing the cable using a pass-through hole,
push it through the hole you drilled in step 12, 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.
2 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 cable ties (not included) 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.
Testing the Installation
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
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.
1 With the boat in the water, turn on the chartplotter.
2 Drive the boat at a slow speed. If the chartplotter appears to
be working properly, gradually increase speed while
observing the chartplotter.
3 If the sonar signal is suddenly lost or the bottom return is
severely degraded, note the speed at which this occurs.
4 Return the boat to the speed at which the signal was lost,
and make moderate turns in both directions while observing
the chartplotter.
5 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.
6 Repeat steps 2–4 until the degradation is eliminated.
7 If the signal does not improve, move the transducer to a
different location on the transom, and repeat the test.
Cleaning the Transducer
Aquatic fouling accumulates quickly and can reduce your
device's performance.
1 Remove the fouling with a soft cloth and mild detergent.
2 If the fouling is severe, use a scouring pad or putty knife to
remove growth.
3 Wipe the device dry.
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.
8 Extract the files to the memory card.
NOTE: The software update can take several minutes to load
onto the memory card.
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.
1 Turn on the chartplotter.
2 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
3 Follow the on-screen instructions.
4 Wait several minutes while the software update process
5 When prompted, leave the memory card in place and restart
the chartplotter manually.
6 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
• Go to
• Keep the original sales receipt, or a photocopy, in a safe
Contacting Garmin Product Support
• Go to for in-country support
• 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.
Transmit power
600 W (RMS)
You may need to update the device software when you install
the device or add an accessory to the device.
Maximum depth*
549 m (1800 ft.)
From 85 to 165 kHz
Loading the New Software on a Memory Card
Operating temperature range From 0° to 50°C (from 32° to 122°F)
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.
1 Insert a memory card into the card slot on the computer.
2 Go to
3 Select Download next to the software bundle that
corresponds with your chartplotter.
NOTE: The software download includes updates for all
devices connected to the chartplotter. Select the correct
bundle that corresponds to the chartplotter to be updated.
You can select See All Devices in this Bundle to confirm the
devices included in your download.
Storage temperature range
Software Update
From -40° to 70°C (from -40° to 158°F)
*Dependent upon the water conditions.
**Dependent upon the chartplotter or fishfinder model.
© 2017 Garmin Ltd. or its subsidiaries
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.
© 2017 Garmin Ltd. or its subsidiaries
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