Great Article by Joe Hyde!
Joe's current article makes a good point. You don't have to own a $50K bass boat to enjoy the advantages of sonar. But the drag of something like a transducer stuck on the hull of a canoe or kayak can spoil the fun.
"Shooting through the hull" solves the problem. From experience I know you can shoot through any hull including aluminum as long as there are no air gaps in the hull and you have a puddle of water to set your transducer in. Since sonar waves are sound waves, they pass through any solid material. Foam sandwich hulls could be a problem.
Joe built a nice custom cup for his transducer. It reminded me of what my friend Bill did with an item you can get at any hardware store. He removed the suction cup from a plumber's plunger, cut a hole in the top of the cup to fit snugly around his transducer, and epoxied the cup to the bottom of his jon boat. Once the boat was in the water, he added water to the inside of the cup and stuck the transducer in. He was ready to "shoot through the hull." No reason you can't do this in any canoe or kayak that has a solid hull.