GT12M-THF 12° Through-Hull CHIRP Mid-Frequency Fishfinder

The Garmin GT12M-THF transducer is made of brass and is specifically designed for installation in fiberglass, wood, or composite hulls. It must not be installed on metal hulls (aluminum or steel) to avoid galvanic corrosion.

The Garmin GT12M-THF transducer is made of brass. This material makes it ideal for installation in fiberglass, wood, or composite hulls.

The GT12M-THF transducer is made of brass. Installing this transducer on an aluminum or steel hull is strongly discouraged as it would create galvanic corrosion. This corrosion can cause significant damage to the hull and water ingress around the transducer.

Yes, it is mandatory to update the software of your Garmin chartplotter after installing the GT12M-THF transducer. This ensures full compatibility and optimal performance of the device.

For optimal performance, the GT12M-THF transducer must be installed in an area with clean, non-turbulent water. Here are some positioning recommendations:

On outboard and sterndrive motorboats: Mount the transducer in front of and close to the motor(s). On inboard motorboats: Mount the transducer in front of and away from the propeller and motor shaft. On stepped hulls: Mount the transducer in front of the first step. General: The transducer must not be mounted behind frames, struts, fittings, water intakes, or discharge outlets, or any other feature that creates air bubbles or turbulent water. It must be parallel to the fore-aft axis of your vessel and must not be installed in a location where it could be struck during launching, towing, or storage.

The main difference between the GT12M-THF and GT15M-THF transducers lies in their construction material and compatibility with hull types:

The GT12M-THF is made of brass and is intended for fiberglass, wood, or composite hulls. It must not be installed on metal hulls. The GT15M-THF is made of stainless steel and is designed for aluminum or steel hulls, featuring galvanic isolation components for these materials.

The Garmin GT12M-THF transducer is made of brass. This material is optimized for installation in fiberglass, wood, or composite hulls.

The "12 degrees" refers to the deadrise angle (hull deadrise angle) preconfigured for the transducer. For optimal sonar performance, it is critical that this angle matches the measured deadrise angle of your boat at the installation location.

To clean the transducer, use a mild household detergent or rubbing alcohol. Do not use solvents such as white spirit, acetone, methyl ethyl ketone (MEK), or similar products. Also avoid electric sanders or pressure washers to clean the transducer to prevent permanent damage to its surface.

The transducer must only be used when fully submerged in water. Operating it in air can cause overheating and damage the transducer. Never use the cable to lift or pull the transducer to avoid damaging both the cable and the transducer itself.

The Garmin GT12M-THF transducer is designed to be installed on fiberglass, wood, or composite hulls.

No, installing the GT12M-THF transducer on an aluminum or steel hull is strongly discouraged. Being made of brass, mounting it on metal hulls would create galvanic corrosion, potentially leading to water ingress around the transducer.

You must check the deadrise angle at the chosen installation location on your boat. This angle can be measured using a smartphone app, an angle finder, a protractor, or a digital level. A 12-degree transducer is suitable for deadrise angles measured between 6 and 16 degrees.

Yes, it is mandatory to update the software of your Garmin chartplotter after installing this transducer to ensure full compatibility and enhanced performance.

For installing the transducer, you will need the following tools:

A drillA 3 mm (1/8 in) drill bitA wrench suitable for nuts up to 75 mmMarine sealant (flexible, fast-curing, for use below the waterline)Mild household detergent or rubbing alcoholSandpaperMasking tapeWaterproof electrical tapeA 73 mm (2 7/8 in) hole saw for fiberglass, wood, or composite hullsMarine-grade epoxy resin for fiberglass (for fiberglass hulls with a core)

For installing the GT12M-THF transducer in a fiberglass hull (solid or cored), you will need a 73 mm (2 7/8 in) hole saw to drill the mounting hole.

For a fiberglass sandwich hull, after drilling a 3 mm pilot hole and applying masking tape, use a 73 mm hole saw to drill completely through the hull from the outside. Then, from the inside, use a slightly larger hole saw to cut only the inner fiberglass skin and the core, taking care not to cut the outer skin. The core must then be sealed with fiberglass or casting epoxy resin to prevent water intrusion.

Optimal positioning depends on your boat's type. The transducer must be installed in an area with clean (non-turbulent) water, free of air bubbles. Avoid zones behind frames, stiffeners, fittings, water inlets, or outlets. It must also be parallel to the boat's fore-aft axis. On outboard or sterndrive motorboats, mount it forward and close to the engine(s). On inboard motorboats, place it forward and away from the propeller and propeller shaft. On stepped-hull boats, mount it forward of the first step. On long-keel boats, install it with a slight angle toward the bow, parallel to the centerline. On wing-keel boats, position it 25 to 75 cm ahead of the keel and no more than 10 cm off the centerline. On displacement-hull boats, mount it about one-third of the waterline length from the bow, and 150 to 300 mm off the centerline.

During installation, you must rotate the transducer from inside the hull until the arrow on top points toward the keel of the boat. This orientation is essential for the internal angle of the transducer to align correctly with the deadrise angle of your boat, ensuring optimal performance.

Yes, cutting or splicing the depth sounder cable, unless required to connect to a "black box" sonar module that needs bare-wire connections, may void your warranty.