I'll try my best here :LOL2: This is all based on my personal experience. The wood on the transom on every aluminum boat that I have owned did not go clear to the bottom of the boat. On my current boat it ends about 1-1/2" above the bottom. So when you mount a transducer you are screwing through just the thickness of your hull not into the wood in the transom. I have done that on several boats. Seal the screws with silicone and you are good to go. Went I upgraded to my current unit, a Humminbird 597 ci HD, I read that the HD units were fussy about having "clean" water around the transducer. My hull is riveted and has strakes. So my placement was determined by my hull design, and trying to avoid the rivets and strakes. By mounting the transducer on a board, the screws from the transducer mount don't go in the the hull, just the board. The board also gives me the ability to move the mount, at least a couple of inches without drilling more holes through the hull. In my opinion your transducer is too high. Try lowering it so it is parallel to the bottom of the hull. Thats were I started with mine, and I had to adjust it lower to get it to read correctly. Again I used a 1/2" board, 3/4" should be fine. It just needs to be thick enough so the screws on the tranducer mount get a good bite without going into the hull.