Garmin GT50M-THP, GT50M-TM, GT51M-TH, GT51M-THP, GT41-TM Installation Instructions

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Thru-Hull Transducer

Installation Instructions

Important Safety Information

WARNING

See the Important Safety and Product Information guide in the product box for product warnings and other important information.

The device must be installed with at least one of the included anti-rotation bolts. Failure to do so could result in the device rotating while the boat is moving and could cause damage to your vessel.

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 to avoid damage to your boat, you must install the Garmin® 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 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.

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.

Go to www.garmin.com/support/software/marine.html.

Select Download next to “Garmin Marine Network with SD

card”. Read and agree to the terms.

Select Download.

If necessary, select Run or save and open the file.

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. The device returns to normal operation after the software

update process is complete. Remove the memory card.

NOTE: If the memory card is removed before the device

restarts fully, the software update is not complete.

Tools Needed

• Drill

• 3 mm bit (1/8 in.)

• 9 mm bit (3/8 in.)

• 13 mm bit (1/2 in.)

• 25 mm spade bit (1 in.) (fiberglass hull)

• 29 mm spade bit (1 1/8 in.) (fiberglass hull)

• 32 mm spade bit (11/4 in.) (fiberglass hull)

• 32 mm hole saw (1 1/4 in.) (metal hull)

• Bandsaw or table saw

• Slip-joint pliers or crescent wrench

• Masking tape

• Marine sealant

• Epoxy or exposed core sealant (cored fiberglass hull)

About the Transducer

The transducer transmits and receives sound waves through the water, and relays sound-wave information to your Garmin sonar device.

Mounting Location Considerations

• On outboard and sterndrive vessels À, the transducer should be mounted in front of and close to the engine or engines.

• On inboard vessels Á, the transducer should be mounted in front of and far away from the engine propeller and shaft.

• On step-hull vessels Â, the transducer should be mounted in front of the first step.

May 2015

Printed in Taiwan 190-01774-02_0B

• On full-keel vessels Ã, the transducer should be mounted at a slight angle that aims at the bow, not parallel to the centerline.

• On fin-keel vessels Ä, the transducer should be mounted from 25 cm to 75 cm (from 10 to 30 in.) in front of the keel and a maximum of 10 cm (4 in.) to the side of the centerline.

• On vessels with displacement hulls Å, the transducer should be mounted approximately 1/3 aft of the waterline length of the vessel from the bow, and from 150 to 300 mm (from 6 to 12 in.) to the side of the centerline.

• The transducer should be mounted parallel to the bow-stern axis of your vessel.

• 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.

Fairing Block Angle Cut

A fairing block positions your transducer parallel to the water line for increased sonar accuracy. You must measure the deadrise angle of your boat hull to determine if a fairing block is necessary to mount the transducer. If the deadrise angle of your mounting location exceeds 5°, you should use a fairing block to mount the transducer.

Deadrise Angle

Deadrise is the angle formed between a horizontal line and a boat hull at a single point. You can measure the deadrise angle with an angle finder, a protractor, or a digital level. You can also ask your boat manufacturer for the deadrise angle of the specific point on your boat hull.

NOTE: A boat may have several deadrise angles depending on the shape of the hull. Measure the deadrise angle only at the location where you plan to install the transducer.

Cutting the Fairing Block

CAUTION

Always wear safety goggles, ear protection, and a dust mask when drilling, cutting, or sanding.

Using wood screws, attach the fairing block to a piece of

wood. The wood becomes a cutting guide for the fairing block. Measure the deadrise angle of the hull at the mounting

location. Tilt your table saw blade À to match the deadrise angle and

secure the cutting fence.

NOTE: The maximum cutting angle of the fairing block is 25°. Cut the fairing block.

Using a rasp or power tool, shape the fairing block to the hull

as precisely as possible. Use the remaining section of the fairing block as the backing

block inside the hull.

Cored Fiberglass Boat Hull Installation Instructions

Thru-Hull Transducer in a Cored Hull with a Fairing Block

If the deadrise angle of your mounting location exceeds 5°, you must use a fairing block to mount the device.

Drilling the Transducer Stem Hole and the Anti-Rotation Bolt Holes in a Cored Fiberglass Hull

Before you can drill holes for the anti-rotation bolts, you must drill the hole for the transducer stem (Drilling the Transducer

Stem Hole and the Anti-Rotation Bolt Holes in a Cored Fiberglass Hull) and you must cut the fairing block (Cutting the Fairing Block).

WARNING

The core must be cut and sealed carefully to protect against water seepage.

Select a mounting location without surface irregularities or

obstructions. Using the template, mark the location of the stem hole and

anti-rotation bolts. Drill a 3 mm (1/8 in.) pilot hole through the template and hull

at the stem hole location.

Position the fairing block on the table so the cutting guide

rests against the fence Á and the angle matches the angle of the mounting location .

Adjust the cutting fence to ensure the fairing block has a

minimum thickness of 13 mm (1/2 in.).

The hole must be perpendicular to the water surface. Place masking tape over the pilot hole and surrounding area

outside the hull to prevent damage to the fiberglass. Using a 25 mm (1 in.) bit at the stem hole location, drill from

outside the hull through the outer skin À, inner skin Á, and the core Â.

The hole must be perpendicular to the water surface. Sand and clean the inner skin, core, and outer skin around

the hole. Seal the exposed inner core with epoxy Ã, and allow the

epoxy to set thoroughly. While holding a drill with a 9 mm (3/8 in.) bit plumb, drill the

anti-rotation bolt holes through the hull from outside the hull. The holes must be perpendicular to the water surface. Sand and clean the area around the holes.

Applying Marine Sealant to a Thru-Hull Transducer

You must apply marine sealant to the transducer to ensure a tight, waterproof seal between the fairing block and the hull. Do not apply sealant directly to the stem or anti-rotation bolts.

Apply marine sealant À around the base of the stem and anti-rotation bolts on the transducer.

Installing the Transducer with a Fairing Block

It is recommended that two installers complete these instructions, with one positioned outside the boat and one inside the boat.

NOTE: When installing the transducer in a cored fiberglass hull, avoid over-tightening the nuts to prevent damaging the hull.

If the anti-rotation bolts À are installed on your transducer,

remove them. Apply marine sealant at the base of the anti-rotation bolts and

transducer stem Á.

From inside the hull, slide the backing block onto the

transducer stem and seat it firmly against the inner hull. The fairing and transducer must be parallel to the keel. From inside the hull, apply the included anti-seize compound

to the exposed transducer stem and anti-rotation bolts. From inside the hull, use slip-joint pliers or a crescent wrench

to secure the backing block to the transducer stem with the included 35 mm hull nut Å, rubber 24 mm washer, and nylon 26 mm washer Æ.

Do not over-tighten the hull nut. From inside the hull, use slip-joint pliers or a crescent wrench

to secure the backing block to the anti-rotation bolts with the included M8 nuts Ç and 8 mm washers È.

Do not over-tighten the M8 nuts. Before the sealant hardens, remove all excess sealant on the

outside of the fairing block and exterior hull to ensure smooth water ﬂow over the transducer.

Thru-Hull Transducer in a Cored Hull without a Fairing Block

If the deadrise angle of your mounting location does not exceed 5°, you can mount the device without a fairing block.

Drilling the Transducer Stem and Anti-Rotation Bolt Holes Using a Template

Seat the transducer housing ﬁrmly within the fairing block

recess. Apply marine sealant to the face of the fairing block that must

contact the hull. Apply marine sealant to the face of the backing block Ã that

must contact the inner hull. From outside the hull, insert the transducer cable Ä and

transducer stem through the mounting hole.

WARNING

You should follow these instructions if you are not using a fairing block or isolator plate to mount your transducer.

Trim the included transducer template.

Select a mounting location without surface irregularities or

obstructions. Using the template, mark the location of the stem hole and

anti-rotation bolts. While holding a 25 mm (1 in.) spade bit plumb, drill the

transducer stem hole from outside the hull. The hole must be perpendicular to the water surface. While holding a drill with an 9 mm (3/8 in.) bit plumb, drill the

anti-rotation bolt holes from outside the hull. The holes must be perpendicular to the water surface. Sand and clean the inner skin, core, and outer skin around

the holes.

Applying Marine Sealant to a Thru-Hull Transducer

You must apply marine sealant to the transducer to ensure a

tight, waterproof seal between the fairing block and the hull. Do not apply sealant directly to the stem or anti-rotation bolts.

Apply marine sealant À around the base of the stem and anti-rotation bolts on the transducer.

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