When kayak fishermen talk about 'thru-hull' they generally mean that the transducer is transmitting through the hull. I have never seen anybody use a real thru-hull transducer on a kayak. You wouldn't want the transducer hard-mounted on the underside of the hull, as it could be damaged when landing. The most common kayak mounting method is to use an adhesive to secure a transducer to the inside of the hull. This method protects the transducer and still provides acceptable sonar performance.
Kayak thru-hull transducer
