I have a Humminbird depth finder with the thru-hull transponder. Any suggestions for a mounting location of the transponder in a 93 Sport Nautique?

i mounted one of these before. it is kind of a pain. You need to mount it in a place that is always in contact with the water and you need to make sure the epoxy has ZERO air bubbles. My installation manual suggested putting some water in the bilge shile you are out on the water and test various locations in the boat. it's tricky

Under the water pump impellar. Starboard side.

I have a 95 Sport and mounted mine on the opposite side (port) lined up with the water pump impeller (of what Peter C wrote). Also, KJ has a good tip with the water in the bilge. I did this to find the best location and used small sand bags to hold the depth finder in one spot.