Overview

The Garmin 010-12378-20 is a TM265LH plastic transom-mount transducer with depth and water temperature, using a 12-pin connection and 1 kW CHIRP low and high bands. It operates across 42 to 65 kHz and 130 to 210 kHz, with a maximum depth rating of 3,000 ft.

On the screen, the low band uses a wider beam for finding bottom in deeper water, while the high band tightens the beam to help separate targets around structure. Beamwidth ranges from 16° to 25° on the low band and 6° to 10° on the high band.

This model is built for transoms with 3° to 21° of angle, and the 39 ft cable gives you room to route from the stern up to the helm or an installed sonar module without extensions.

Key features

• 1 kW CHIRP Low and High coverage: 42 to 65 kHz and 130 to 210 kHz
• Maximum depth rating up to 3,000 ft for offshore and deep-water use
• Beamwidth options: 16° to 25° (low) and 6° to 10° (high) for wider search or tighter target separation
• Depth and water temperature sensing; no speed sensor in this model
• 12-pin plug for compatible Garmin sonar-capable displays and sounder modules
• Supported transom angles: 3° to 21°
• 39 ft cable for practical routing on center consoles, pilothouse boats, and larger rigs

Compatibility and fit

This is a transom-mount CHIRP depth transducer, so it needs a compatible Garmin sonar system that supports a 12-pin transducer connection and 1 kW CHIRP operation. Before ordering, confirm your unit has the correct transducer port and sonar capability for a low/high CHIRP 1 kW transducer.

Transom-mount transducers work best when they can sit in clean water at speed. If your hull has steps, strakes, or heavy aeration near the mounting area, plan placement carefully so the face stays in solid water when the boat is running and turning.

Installation and setup

Mounting position matters more than anything else. Place the transducer where it will see smooth water flow, keep it clear of the propeller swing radius, and leave enough space above the bracket for it to release and kick up if it strikes an object. A small adjustment up or down can make a big difference in bottom tracking at speed.

Route the cable well above standing water in the bilge, support it to prevent vibration wear, and keep it away from sharp edges and high-heat areas. Avoid cutting or splicing the transducer cable; if a splice is unavoidable, use a purpose-built watertight junction method intended for transducer cables.

Use on board

This transducer is a solid match for boats that spend time in deeper water and want bottom detail that stays readable, while still having a tighter beam option for working structure and bait on the high band. It also fits well for crews that want reliable depth plus water temperature without adding a separate temp sensor.