Shoot-through-hull (in-hull) transducer installation mounts the transducer inside the boat, bonded to the inside of the hull and reading sonar signals through the hull material itself. No drilling required. Here's when it works and when it doesn't.
When Shoot-Through Works
Shoot-through installation only works through solid fiberglass. The hull material must be a uniform solid laminate — no air gaps, no foam core, no balsa core. The sonar signal passes through the fiberglass and water-couples at the hull/water interface on the exterior surface. Any air gap (from cored construction) reflects the signal back rather than transmitting it, producing no usable reading.
How to test your hull: knock on the interior hull surface firmly in several locations. A solid thud = solid fiberglass = shoot-through compatible. A hollow resonant sound = cored construction = shoot-through won't work. For certainty, use a moisture meter on the hull — solid glass gives consistent readings; cored hulls give variable readings.
Performance Trade-Off
Shoot-through installations lose approximately 30–50% of sonar depth penetration and resolution compared to an in-water transom mount. In practice for freshwater fishing under 150 ft on clear lakes, this is often acceptable. For fishing deep water (200+ ft), offshore work, or heavily stained water where sonar performance is already challenged, shoot-through's performance reduction becomes a real limitation.
Installation Process
- Identify a location in the bilge area below the waterline, ahead of any strakes, behind the deadrise rise (the lowest, flattest part of the hull bottom), and away from the keel or any hull hardware. This location produces the clearest signal.
- Clean and dry the hull interior where the transducer will bond — any wax, oil, or moisture interferes with the epoxy bond.
- Fill the transducer housing's contact area with epoxy (not silicone — silicone compresses and introduces an air gap). Press the transducer firmly into the epoxy against the hull surface and hold until the epoxy begins to cure.
- Allow full cure per the epoxy manufacturer's specs (typically 24–72 hours) before testing.
- Test in water — you should get a depth reading immediately. If not, inspect for air bubbles in the epoxy bond.
The standard in-hull shoot-through transducer — polyurethane housing bonds with epoxy, reads through solid fiberglass. 200 kHz standard frequency.