Overview

The Garmin Fishfinder 340C is a 5.0-inch color sonar display built for small-boat installs where you want a dedicated sounder at the helm or nav station. It runs on 10 to 33 V DC and uses a fully gasketed case that is waterproof to IPX7, so it tolerates spray and the kind of wet handling that happens on deck.

It uses a 256-color TFT screen with adjustable brightness (234 x 320 pixels) and supports both dual-frequency and dual-beam sonar, depending on the transducer package. Dual-frequency sonar is rated to 1,500 ft and dual-beam sonar is rated to 900 ft, with real-world depth always changing with salinity, bottom type, and sea conditions.

For system integration, it supports NMEA 0183 (version 3.01) input and output and can share full sonar screens over Garmin CANet with compatible chartplotters when the proper network kit is installed.

Key features

• 5.0-inch diagonal color display with adjustable brightness (234 x 320 pixels)
• Waterproof to IPX7 with a fully gasketed, high-impact plastic alloy case
• 10 to 33 V DC power input with a 3.0 A AGC/3AG fuse; up to 17 W max at 10 V DC and 15 W at 13.8 V DC nominal
• Dual-frequency sonar: 50/200 kHz, 500 W RMS (4,000 W peak to peak), rated to 1,500 ft
• Dual-beam sonar: 80/200 kHz, 400 W RMS (3,200 W peak to peak), rated to 900 ft
• NMEA 0183 (v3.01) input/output for sharing depth, temperature, and speed data (with a capable transducer) and receiving navigation data from a GPS
• Garmin CANet compatible for sharing full sonar pages with compatible chartplotters when networked
• Mounting options include a tilt and swivel bracket or a flush-mount install

Variants

This product is offered in multiple package configurations that change what transducer is included.

All packages use the same Fishfinder 340C display and core mounting and cabling parts, while the transducer option (or no transducer) changes the sonar frequency set, mounting style, and the published depth capability.

• 010-00505-00: Fishfinder 340C, no transducer included. This configuration works well when the boat already has a compatible transducer installed or when you want to match a different transducer style to your hull and operating depth.
• 010-00505-01: Fishfinder 340C with dual-beam transducer (14°/45°) for trolling motor or transom mounting, with depth and temperature and an attached 30-foot cable. The two cone angles give a tighter look for detail or a wider look for coverage.
• 010-00505-02: Fishfinder 340C with dual-frequency transducer (200/50 kHz) for transom mounting, with depth and temperature and an attached 30-foot cable. The 50 kHz channel is commonly used when you need more reach in deeper water, while 200 kHz is used for a more detailed picture.

What’s included

• Fishfinder 340C unit
• Tilt/swivel mount
• 6-foot data/power cable
• Owner’s manual
• Quick reference guide
• Flush mount template
• Protective cover
• Flush mount hardware kit

Installation and setup

The unit can be bracket-mounted on a console or overhead, or flush-mounted into a flat panel using the supplied template. Plan for at least 3 inches (8 cm) of clearance behind the case so the connectors and cables can route cleanly without tight bends.

Pick a mounting spot where the screen stays readable while running and the keypad is easy to reach. Avoid locations with extended exposure outside the operating temperature range of 5°F to 131°F (-15°C to 55°C), since excessive heat in an enclosed console can shorten screen life.

Electrical and system integration

Power is straightforward on typical 12 V and 24 V boats: connect the red wire to positive and the black wire to ground, and protect the circuit with the specified 3.0 A fuse. If you extend the power leads, use 22 AWG wire and keep connections clean and supported so vibration does not fatigue the conductors.

The wiring harness also supports NMEA 0183 input and output for sharing sonar data and receiving navigation information from a GPS or other compatible device. For full sonar sharing over Garmin CANet, the unit can be connected into a CANet network with the appropriate CANet kit.

On-water use

Once the transducer is installed and the boat is in the water, the sonar pages can be tuned with features like Auto Gain, zoom (2x and 4x), Whiteline for bottom interpretation, and on-screen tools such as A-scope when enabled. The unit can also log water temperature when a temperature-capable transducer is used and supports alarms such as shallow and deep water, fish, and low battery.

This model is a good match for skippers who want a dedicated fishfinder screen on a smaller helm, or for anglers adding a second sonar view on a networked Garmin setup.

Maintenance and care

Clean the case with a cloth dampened with a mild detergent solution and wipe dry. For the screen, use eyeglass lens cleaner on a clean, lint-free cloth and avoid ammonia-based cleaners that can damage the coating.

If the unit is submerged, wipe it down and let it air dry before powering it back up.