Garmin Striker 4: Flashing Depth Issue - Diagnosis

⚠️ SAFETY WARNING. Incorrect intervention on this device may lead to unforeseen risks or void the warranty. It is recommended not to proceed without adequate technical skills. ReeFix provides this diagnosis EXCLUSIVELY for educational and informational purposes.

TECHNICAL CHECKLIST

Preliminary Checks (User Action)

1. External visual inspection: Check the hull forward of the transducer. Look for obstacles (thru-hulls, other sensors, sharp edges, anti-fouling build-up) that could generate air bubbles.
2. Transducer integrity verification: Ensure the bottom surface of the transducer is smooth, without deep scratches, marine growth, or non-specific anti-fouling paint (copper-based ones attenuate the signal).
3. Bracket check: Visually verify that the Garmin Striker Transducer Mounting Bracket is not loose, deformed, or damaged.
4. In-water test: Navigate at low speed, then gradually accelerate. If the depth flashes only at high speed or when planing, it is almost certainly an installation issue.

Professional Inspection (Technician Action)

A qualified technician will follow a specific protocol:

1. Hull flow analysis: Evaluation of the water flow line forward of the transducer to identify sources of turbulence or air bubbles.
2. Height adjustment: Precise measurement of the transducer's height relative to the hull bottom (1-3 mm below for fiberglass, flush for aluminum).
3. Angle (pitch) adjustment: Setting the longitudinal inclination of the transducer (1-3 degrees downwards) to ensure constant contact with clean water.
4. Lateral positioning: Verify that the transducer is on the starboard side (for right-hand propellers) and at least 25-30 cm from the propeller's radius to avoid turbulence and exhaust gases.
5. Mechanical stability: Flex test of the mounting bracket to rule out movement under hydrodynamic load.

Tools and Spare Parts

• Garmin Striker Transducer Mounting Bracket: Essential for replacement in case of wear, mechanical play, or breakage of the original support.
• Garmin GT20-TM Transducer: Replacement sensor (compatible with ClearVü/Vivid versions) to be replaced in case of cracks or water infiltration.

If your Garmin GT20-TM does not read depth or only shows dashed lines on the screen even when the boat is stationary, the internal sensor may be damaged. In these cases, replacing the transducer is the only solution to restore correct bottom readings.

• SikaFlex 291i Marine Sealant: Specific polyurethane adhesive sealant to ensure waterproofing of mounting holes on the transom.
• Spirit level: Essential tool for verifying the correct alignment and inclination of the transducer relative to the waterline.

Safety Notes

Any physical intervention on the vessel or transducer must be performed with the engine off, the vessel out of water (hauled out), or in conditions of complete safety. Before working on electrical wiring or sonar connections, disconnect the 12V power supply from the onboard battery to prevent accidental short circuits or damage to lithium/lead cells.

INSPECTION RESULT

Cause Analysis and Probability

Flashing depth on the Garmin Striker 4 display at speed indicates a loss of bottom tracking, almost always due to aeration (air bubbles) on the transducer surface. Air bubbles reflect or scatter ultrasound, preventing the signal from reaching the bottom and returning to the sensor.

1. Incorrect transducer height/angle (Cavitation) — 65%

   • Why: If the transducer is mounted too high or at an incorrect angle, it draws air or creates its own turbulence as soon as the boat gains speed and planes.
   • Key signals: Perfect operation at low speeds or when stationary; the problem systematically appears when accelerating. Excessive stern spray.
   • Often happens when: Installation was not performed with millimeter precision or was not optimized for the boat's specific hydrodynamics.
   • Verification: Measure height and angle with a spirit level and a straight edge placed against the hull.

2. Positioning in turbulence wake (Strakes or Propeller) — 20%

   • Why: The transducer is mounted in an area where water flow is already disturbed by other hull appendages (strakes, thru-hulls, other sensors) or the propeller wake. The propeller, especially if right-handed, creates more turbulence on the port side of the stern.
   • Key signals: The problem also occurs at moderate speeds, when turning, or when the engine is under strain. The transducer is on the port side or directly behind a hull element.
   • Verification: Examine the hull to identify sources of turbulence forward of the transducer and its position relative to the propeller.

3. Mechanical flex or loose bracket or transducer damage — 10%

   • Why: An unstable or damaged bracket can cause the transducer to lift out of clean water at high speeds. A transducer with cracks or infiltrations loses sensitivity.
   • Key signals: The problem only appears at very high speeds. The bracket moves or flexes to the touch. The transducer surface shows cracks or impact marks.
   • Verification: Manual inspection of the bracket and visual inspection of the transducer for physical damage.

Output for Technician

"The Garmin Striker 4 fishfinder exhibits systematic loss of bottom tracking during planing, with flashing depth. Aeration/cavitation on the active face of the transom-mounted transducer is suspected. Verification of fluid dynamic positioning is required: height relative to the hull bottom, pitch angle, and lateral positioning relative to the propeller/strakes. Evaluate bracket and transducer integrity. Perform structural polyurethane sealing of holes if necessary."

OPERATIONAL DECISION: If preliminary checks indicate an installation problem (cause 1 or 2), consult a specialized technician for precise adjustment; if the bracket is damaged or the transducer has cracks (cause 3), consider replacing the component or the entire device based on the cost of professional repair.