GDT™ 43 Through-Hull Depth/Temperature Sensor

The Garmin GDT™ 43 transducer is designed to accurately measure water depth and temperature. It operates at a frequency of 50 kHz and provides a transmit power of 300 Watts.

The GDT™ 43 transducer can measure depths up to 152 metres (500 feet).

The GDT™ 43 transducer is made of plastic, ensuring durability suited to the marine environment.

The GDT™ 43 transducer is compatible with NMEA 2000® networks via a NMEA 2000® adapter (not included) or directly with a NMEA 0183 system.

Yes, the GDT™ 43 transducer is designed to directly replace existing Nexus and Silva 43 mm (TH43) through-hull transducers, making upgrades straightforward.

The GDT™ 43 transducer is compatible with hulls having a deadrise angle of 0 to 20 degrees.

For installation of the GDT™ 43 transducer, you will need the following tools:

A drillA 43 mm (1 11/16 in) hole sawA 52 to 55 mm (2 1/16 to 2 3/16 in) hole saw for sandwich fiberglass hullsMarine sealantSilicone greaseA cable cutterA metal file (for metal hulls)Fiberglass cloth and resin (optional for sealing a sandwich fiberglass hull)A 43 mm (1 11/16 in) cylinder, wax, tape, and casting epoxy (optional for sealing a sandwich fiberglass hull)

On keel-and-fin sailboats, the depth sounder must be mounted more than 25 cm (10 in) and less than 75 cm (30 in) ahead of the keel, and less than 10 cm (4 in) off the centerline.

Yes, for optimal performance, the transducer must not be mounted:

Behind strakes, skegs, fittings, through-hull fittings, or any scuppers or water discharge outlets, or anything that creates air bubbles or causes turbulent water.
In a location where it could be shaken during launching, hauling, or storage.
Near the edge of sharp hull strakes on powerboats.
In the path of the propeller on single-propulsion boats.

To prepare a sandwich fiberglass hull, first drill a 3 mm (1/8 in) pilot hole through the hull. Then, from the outside, cut a 43 mm hole through the outer skin only. Inside, cut a 9–12 mm larger hole through the inner skin and most of the core, without cutting the outer skin. Remove the cut core and inner skin, sand and clean the area. Finally, seal the core using layers of fiberglass cloth and resin, or with casting epoxy and a spacer sleeve.

It is crucial to properly seal the core of a fiberglass sandwich hull to prevent water from seeping into the core, which could seriously damage the boat.

The GDT™ 43 transducer connects to the NMEA 2000® network via a NMEA 2000® adapter. This adapter must then be connected to a NMEA 2000® T-connector that is part of the network.

No, the NMEA 2000® adapter is not included with the GDT™ 43 transducer and must be purchased separately.

General installation steps include:

Cut a 43 mm hole in the hull.Insert the through-hull fitting.Apply marine sealant to the outer flange of the fitting and hand-tighten the nut.Slide the O-rings onto the plug and apply silicone grease.Insert the plug into the fitting.Ensure the plug is seated correctly.Install the fitting with the pin at 90 degrees to the boat’s centerline.After the sealant has cured, remove the nut, apply sealant inside the hull, then reinstall and hand-tighten the nut.Replace the plug with the actual transducer.Install the wire locking device on the transducer.

It is recommended to keep the cap for cleaning or maintenance of your transducer.

Yes, the retractable design of the transducer minimizes fouling. Additionally, the supplied cap can be used when cleaning or servicing your transducer.

You must use a 43 mm (1 11/16 in) hole saw to drill the hole in the hull. For sandwich fiberglass hulls, a 52 to 55 mm (2 1/16 to 2 3/16 in) hole saw is also required to prepare the core.

An NMEA 2000 drop cable, used to connect a device to the main backbone network, is limited to a maximum length of 6 meters (20 feet).

NMEA 2000 devices must operate on a 9–16 V DC supply with a nominal 12 V DC voltage.

To ensure optimal performance of your Garmin GDT™ 43 through-hull transducer, selecting the correct mounting location is critical. Key considerations vary by hull type and general best practices:

On fin keel sailboats: The transducer must be mounted more than 25 cm (10 in) and less than 75 cm (30 in) ahead of the keel, and within 10 cm (4 in) of the centerline.
On full keel sailboats: The transducer should be mounted at a slight angle toward the bow, not parallel to the centerline.
On powerboats and hard-chine hulls: Avoid mounting the transducer near the sharp edges of the hull chines.
On single-screw boats: The transducer must not be mounted in the propeller wash.
On twin-screw boats: If possible, mount the transducer between the two propellers.
General rules for all hull types:

The transducer must be mounted parallel to the fore-aft axis of the vessel.
Select a location that allows easy access to the transducer from inside the boat.
Avoid mounting the transducer behind hull chines, stiffeners, fittings, through-hull fittings, or any element that may create air bubbles or turbulent water. The transducer must always be in smooth (non-turbulent) water for optimal performance.
Do not mount the transducer where it could be struck during launching, beaching, or storage.
Be aware that the transducer may cause cavitation, which can degrade boat performance and damage the propeller.