Transducer
Not a problem using a thru hull inside as a shoot through. Providing you find a clean spot in the hull, and have no bubbles in the glass, or in whatever you use to fasten it down. Cored hulls don't do well, but a solid glass hull will do fine. Put it in a baggie of water, sit it in the bottom of the hull where you want to mount it, and turn the finder on. Move the baggie around till you find a spot that works well. Then clean the spot good, maybe a light sanding and a wipe down with acetone, and mount the ducer. Some use 5200 for mounting, others lots of different things. Think I saw one post that they poster used a wax toilet bowl ring. I prefer Marine Tex. Just make sure there are no air bubbles anywhere under the ducer. No bubbles, no problem.