Fill hole with what?

[jvitiel]

Epoxy the inside of the hole and put a single hole laboratory stopper under the clam shell. Secure enough yet easy to remove.

https://www.medical-and-lab-supplies...ole-qty-1.html

[phatdaddy]

great idea, jv. don't tell it's going on a boat, it'll be $10.76

[steplift20]

I like the idea but 5200 is impossible to remove some time in the future wouldn't 4200 be better?

[spareparts]

use a hole saw and cut a plug out of another piece of wood. Cut a key hole in teh plug for the transducer. Epoxy seal both the plug and the hole in the transom, slip the plug over the cable, silicone the outside of teh plug and slide it in the hole, Put a clam shell over it. If you ever need to remove the plug you can knock it out