Garmin GPSMAP 178C Owner's Manual page 109

To avoid drilling a hole to mount a thru-hull transducer, a transom mount transducer may be used
with epoxy inside a boat ("shoot-thru-hull" installation). For a transducer to be mounted inside the
hull (shoot-thru, not thru-hull), the boat must be fi berglass, no core (contact your boat manufacturer if
you are unsure). Test by placing a small amount of water inside the hull, placing the transducer on top
of the water, then verifying the accuracy of the locators versus the current water depth. If they are the
same, use slow-curing epoxy (non-silicone based) to affi x the transducer to the inside of the hull.
Shoot-Thru-Hull Installation
The transducer is designed to be mounted inside a fi berglass hull. The standard plastic transom
mount transducer can also be mounted in this fashion using this method. If using a temperature sens-
ing transducer, the temperature displayed refl ects the hull temperature.
Selecting a location:
1. The location has to be solid fi berglass, devoid of any air bubbles, laminates, fi llers or dead air space.
The location needs to be in an area of clean water at all speeds. Do not place the transducer over
any strakes or behind any obstruction on the hull that would create turbulence at speed.
NOTE: Many modern hulls have a prelocated pocket for shoot-thru-hull transducer
installation. If you are unsure if your hull is equipped with a pre-located pocket,
contact your hull manufacturer.
Testing the location:
1. Place the transducer in the water, pointed directly at the bottom and set unit for optimum perfor-
mance. Place the transducer in the test device as show on the side bar. If the sonar performance is
signifi cantly degraded, another location needs to be tested.
Installing the transducer:
1. Lightly sand the surface of the hull and face of the transducer with 400 grit wet or dry sandpaper.
2. Build a dam using strip caulk about 1/4" tall. Pour about 1/8" of two part, slow cure epoxy in the
dam. Place the transducer in the epoxy, turning the transducer to work out any air bubbles.
3. Weight the transducer in place and allow to cure for 24 hours.
Appendix A
Mounting the Transducer
Weight transducer
PVC Pipe
to hold it in place
or a Can
Strip Caulk
or RTV Sealer
Hull Surface
Testing the Location
Fill Pipe or Can
with water or a
light mineral oil
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