Anyone know if you can shoot they the hull of a kayak with this graph or does the transducer have to be in the water? I searched around and can't seem to find an answer. The plastic on the kayak is relatively thin and no where near as thick as a glass boat. The only answers I seem to be able to find reference thick glass hulls and aluminum hulls on larger boats.

Thanks in advance

For optimum results, yes it is recommended that all HDI transducers must be in direct contact with the water.  With this said, I do know some with fiberglass bass boats that have mounted them as a shoot-thru and are content with it.