My P-28 is not a plywood boat but the hull is wood core- so essentially the same thing. My transducer came with a two part plastic fitting that was supposed to fit through a hole in the bottom of the boat. Holds the sending unit and screws together to make the assembly waterproof. I did not like that idea at all. What I did was to hole saw down to the outer glass skin, removed all the wood and epoxied a piece of PVC pipe into the hole. I then filled the bottom of the pipe with CLEAR epoxy to come back to the original hull thickness. You want clear to make sure there are no air bubbles. It's the air that degrades/kills the signal. After it cures fill the pipe with mineral oil, drop the sending unit in and put a PVC cap on and away you go. Your pipe needs to be just a smidgen bigger that your sending unit so the sender does not bounce around. It also needs to be totally full of oil. Again you don't want any air bubbles. Mine works really well and I have one less through hull to worry about. Good luck PeterP