Garmin Fishfinder 400C Owner's Manual - Page 14

Installing the Fishfinder 400C 6. Mark the location. Using a 1/8" bit, drill a pilot hole approximately 3/8" (10 mm) deep. 7. Attach the cable clamp using a 4 x 12 mm screw. Coat the screw with marine sealant before installation. Repeat steps 5 and 6 using the other cable clamp. 8. Route the transducer cable, as needed, to the fishfinder. DO NOT CUT THE CABLE. Avoid routing the cable with electrical wires or other sources of electrical interference. Drill pilot holes here. Level Vertical Align with the transom bottom. The transducer should extend 1/8" below fiberglass hulls or 3/8" below aluminum hulls. Bottom of the transom Shoot-Thru-Hull Installation To avoid drilling a hole to mount a thru-hull transducer, a transducer can be secured with epoxy inside a boat (shoot-thruhull installation). This type of installation can provide better noise reduction and allow you to use a higher Gain setting. For a transducer to be mounted inside the hull (shoot-thru, not thruhull), the boat must be fiberglass, with no core. Contact your boat manufacturer if you are unsure. Professional installation might be necessary. Some transducers are specifically designed to be mounted inside a fiberglass hull. The standard plastic transom mount transducer can also be mounted using this method. If using a temperature sensing transducer, the temperature shown reflects the hull temperature. Keep it parallel with the water line. OK  Fishfinder 400C Owner's Manual