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

The Garmin GT12M-THF transducer is made of brass and is specifically designed for installation in fiberglass, wood, or composite hulls. It is critical not to install it 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 depth sounder. This ensures full compatibility and optimal performance of the device.

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

On outboard and sterndrive motorboats: Mount the transducer in front of and close to the engine(s).On inboard motorboats: Mount the transducer in front of and away from the propeller and propeller shaft.General: The transducer must not be mounted behind frames, stiffeners, fittings, water intakes, or drain holes, 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 mounted in a location where it could be struck during launching, towing, or storage.

The main difference between the GT12M-THF and GT15M-THF depth sounders 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 angle) preconfigured for the transducer. For optimal sonar performance, it is crucial 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 isopropyl alcohol. Do not use solvents such as white spirit, acetone, methyl ethyl ketone (MEK), or similar products. Do not use an electric sander or high-pressure washer to clean the transducer, as this may permanently damage its surface.

The transducer must only be used when fully submerged in water. Operating it in open air can cause overheating and damage the transducer. Additionally, 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 for installation on fiberglass, wood, or composite hulls.

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

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

Yes, it is imperative to update the software on your Garmin chartplotter after installing this depth sounder to ensure full compatibility and improved performance.

To install 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 sandwich hulls)

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

For a cored-fiberglass 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 ingress.

Optimal positioning depends on your boat type. The depth sounder must be installed in an area with clean (non-turbulent) water, free of air bubbles. Avoid zones behind frames, struts, fittings, water intake or outlet openings. It must also be parallel to the boat's fore-aft axis. On outboard or sterndrive-powered boats, install it forward and near the engine(s). On inboard-powered boats, place it forward and away from the propeller and propeller shaft. On vee-bottom hulls, install it forward of the first chine. On long-keel boats, install it with a slight angle pointing forward, parallel to the centerline. On wing-keel boats, place it 25 to 75 cm ahead of the keel and no more than 10 cm off the centerline. On displacement hulls, install it about 1/3 of the waterline length from the bow, and 150 to 300 mm off the centerline.

During installation, rotate the depth sounder from inside the hull until the arrow on top points toward the keel. This orientation is critical so that the internal angle of the depth sounder aligns with your boat’s deadrise angle, 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.