I cannot tell
of any loss by shooting throught the hull with a Hawkeye, depth finder, or with the newer Garmin I have. I would much prefer this to drilling another hole in my boat below the water line. Put the transducer in a baggie of water, sit it in the bottom where you think you want it, and move it around till you get the best return. Then epoxy it there. Just be sure you have no air bubbles in the epoxy. Unless of course you have a cored hull, then you don't have much choice. As to which unit, I have one of the Hawkeyes, and they work very good. There are several choices for under 100 bucks.