Install A Transducer Without Holes Below The WaterlinePublished: Fall 2013
Two ways to install a transducer that won't compromise your hull.
Method 1: Substitute Transom
There are alternatives to drilling a hole in your bottom for a transducer. Transom-mount transducers are common on smaller boats, but the mounting screw holes can allow water in, causing rot in the transom core. Even careful sealing will eventually fail because of the stress of running on plane. A better option uses a piece of "plastic wood" such as structural grade Starboard as a mounting point. Cut a piece long enough to extend from the bottom of the transom to a point at least six inches above the waterline, and several inches wider than the mount. Thru-bolt it to the transom using four stainless bolts. All holes should be well above the waterline and fit the bolts snugly. Dry fit everything, carefully following depth finder instructions, to be sure you've got the right fit and positioning.
Seal the transom core inside the bolt Install A Transducer Without Holes Below The Waterline Two ways to install a transducer that won't compromise your hull holes with epoxy resin. Use a syringe to inject the resin into the hole and a Q-tip or toothbrush to spread it around inside. Do this immediately before you insert the bolts. Seal and "glue" the board to the transom with 3M 5200 applied over the back of the board. The bottom edge of the board should be approximately 1/4- inch above the bottom of the boat and far enough above the bottom of the hull to avoid turbulence. Taper the bottom edge of the board, making it parallel to the surface of the water when running on plane. Mounting screw holes in the board now shouldn't puncture the transom; you'll have room for mistakes and the ability to add different transducers later.
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To find the right spot inside your hull, experiment by filling a Ziploc bag with water and placing the transducer inside. Sit the transducer and bag down against the test areas while running the boat to find one that works well.