Before you epoxy it to the hull you can put the transducer in the hull and add enough water to the bilge to cover the puck. Then put a gallon ziploc of sand or dirt on top to hold it in place. That way you can move it around if it doesnt read correctly at speed. Once you find the sweet spot you can epoxy it in, or use a good marine grade silicone in case you think you may want to move it later. Be careful with the silicone. A little goes a long way, and can be very difficult to remove if you dont have enough room to get some leverage to pry it up.
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