Garmin GT21-TH ndash; Stainless Steel Thru-Hull DownVuuml; 500 W CHIRP 260/455 k - Page 6
Metal Boat Hull Installation Instructions
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2 Using the template, mark the location of the stem hole and anti-rotation bolts. 3 Drill a 3 mm (1/8 in.) pilot hole through the ull at the stem hole location, from outside the hole. The hole must be perpendicular to the water surface. 4 Using a 32 mm (1 1/ 4 in.) hole saw, cut the stem hole from outside the hull. The hole must be perpendicular to the water surface. 5 While holding a drill with a 13 mm (1/2 in.) bit plumb, drill the anti-rotation bolt holes through the hull from outside the hull. 6 Sand and clean the area around the holes. Applying Marine Sealant to a Thru-Hull Transducer You must apply marine sealant to the transducer to ensure a tight, waterproof seal between the fairing block and the hull. Do not apply sealant directly to the stem or anti-rotation bolts. Apply marine sealant around the base of the stem and À anti-rotation bolts on the transducer. 2 From outside the hull, insert the transducer through the mounting hole and seat it firmly against the hull. 3 From inside the hull, apply the included anti-seize compound to the exposed transducer stem and anti-rotation bolts. 4 From inside the hull, use slip-joint pliers or a crescent wrench to secure the included 35 mm hull nut , 26 mm nylon à washer , and 24 mm rubber washer to the transducer Ä Å stem. Do not over-tighten the hull nut. 5 From inside the hull, use slip-joint pliers or a crescent wrench to secure the included M8 nuts and 8 mm nylon washers to Æ the anti-rotation bolts. Do not over-tighten the M8 nuts. 6 Before the sealant hardens, remove all excess sealant on the outside of the exterior hull to ensure smooth water flow over the transducer. Installing the Transducer with a Fairing Block It is recommended that two installers complete these instructions, with one positioned outside the boat and one inside the boat. 1 Secure the bushings to the anti-rotation bolts and À Á transducer stem .  Metal Boat Hull Installation Instructions Thru-Hull Transducer in a Metal Hull with a Fairing Block If the deadrise angle of your mounting location exceeds 5°, you should use a fairing block to mount the device. Drilling the Transducer Stem Hole and the Anti-Rotation Bolt Holes in a Metal Hull You should follow these instructions when you are using a fairing block to mount the transducer on a boat that has a metal hull. 1 Select a mounting location without surface irregularities or obstructions. 6 2 Apply marine sealant to the bushings, and at the base of the anti-rotation bolts and transducer stem. 3 Seat the transducer housing firmly within the fairing block à recess. 4 Apply marine sealant to the side of the fairing block that must contact the hull. 5 Apply marine sealant to the side of the backing block that Ä must contact the hull.