Your Humminbird will work fine without doing anything fancy or permanent.
It will shoot right through fiberglass or aluminum. I've done it for years.
Using any type of tape, make a ridge (about the diameter) of a tuna can) somewhere on the inside hull of the vessel. Drip a little water from your paddle into the little pond, and set the transducer in the water. The transduver does not have to be submerged, you just need a little water between the face of the transducer and the hull.
This will reduce the sensitivity slightly. The unit may now only work well to 500' depth, not the 600' advertised.
I've even used mine when ice-fishing. Poor a little water from your water bottle on the smooth ice, then sit the transducer on the puddle.
Touring Kayak Paddles
Heel and Pegpads™
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