GT21-TM – Sonda zadní tabule TA ClearVü CHIRP 500W (260/455 kHz) a tradiční 600W (50/200 kHz) + čidlo teploty (8-pin)

The Garmin GT21-TM is a transom-mount fishfinder designed to be installed externally at the rear of the boat. It combines traditional sonar and CHIRP ClearVü scanning sonar technologies.

The GT21-TM transducer uses two main sonar technologies:

Traditional sonar, which provides clear fish arches and excellent target separation. CHIRP ClearVü scanning sonar, which delivers near-photographic images of underwater structures and fish beneath your boat.

The GT21-TM transducer’s traditional sonar operates on 50/200 kHz frequencies with 600 W power.

The CHIRP ClearVü sonar of the GT21-TM transducer operates on frequencies of 260/455 kHz (CHIRP ranges: 245-275 kHz and 445-465 kHz) with a power output of 500 W.

The GT21-TM transducer can reach a maximum depth of 457 metres (1,500 feet) using traditional sonar (50/200 kHz) and 305 metres (1,000 feet) with CHIRP ClearVü sonar (260/455 kHz).

Yes, the Garmin GT21-TM transducer is equipped with an integrated fast-response temperature sensor.

The GT21-TM transducer is supplied with a 9.1 m (30 ft) cable and features an 8-pin connector.

The GT21-TM transducer beam angles are:

For traditional sonar: 40°/10°. For CHIRP ClearVü sonar: 2.0°x51° at 260 kHz and 1.4°x29° at 455 kHz.

The GT21-TM transducer is a transom-mounted transducer. It must be mounted at the rear of the boat’s transom using a bracket and screws. Installation requires drilling holes in the transom for the bracket and potentially for cable routing. It is critical to install it so that it has direct, unobstructed contact with smooth water, away from turbulence.

To install the GT21-TM transducer, you will need the following tools:

A drill and drill bits.Two 13 mm hex keys.A #2 Phillips screwdriver.Masking tape.Marine sealant.

For optimal performance, the transducer must be mounted:

As close as possible to the center of the boat.Far from propellers, strakes, reinforcements, water intakes or discharges, and anything that could create air bubbles or turbulence.In an area where it cannot be damaged during launching, towing, or storage.Parallel to the boat’s waterline.

To minimize interference:

Mount the transducer away from electromagnetic interference sources (electronic devices, engines, radar) and acoustic interference sources (other transducers, boat machinery, wind, waves). Avoid turbulence zones caused by hull features or propeller wash. If the transducer cable must cross a power cable, orient the cables at 90 degrees. If using multiple transducers, mount them at least 60 cm (24 inches) apart and avoid operating two transducers of the same frequency simultaneously.

For the 8-pin cable of the GT21-TM transducer, you will need to drill a 25 mm (1 inch) diameter through-hole in the transom.

Yes, it is essential to apply marine sealant around all screws and around the cable where it passes through the transom to ensure watertightness and prevent any water ingress into the boat.

No, it is strongly recommended to mount the transducer away from the propeller. The propeller wash creates turbulence that can interfere with the fishfinder signal and damage both the transducer and the propeller. Mount it at least 38 cm (15 inches) from the propeller and on the side opposite to the propeller’s rotation direction.

To test the installation:

Put the boat in the water and turn on the chartplotter.Drive the boat at low speed and check that the depth sounder is working properly.Increase speed gradually while monitoring the chartplotter.Note the speed at which the signal is lost or degraded.If the signal is lost, return to the speed where the loss occurred and make moderate turns in both directions.If the signal improves while turning, adjust the transducer 3 mm (1/8 in) lower.Repeat steps until the degradation is eliminated. If the signal does not improve, consider relocating the transducer.

Yes, as a transom-mount transducer, the GT21-TM is compatible with all hull materials.

The GT21-TM transducer is not recommended for use on sailboats due to excessive heel. For deep-V hulls, mount the transducer at the lowest point before the first chine and away from other hull features that create turbulence.