I am fitting anew NASA Clipper depth to a steel hull 6mm thick. So far as I can see it is intended to be mounted inside the hull. Will this work through a steel hull?
This is what I assume you must do, but take expert advice, I am not expert at anything except wasting time, which is why I'm here.
You build up a steel fairing to go outside, welded the hull, to protect the transducer from impact damage, so that only the bottom face of the transducer is open to the sea. Then drill a hole in the boat large enough for the transducer stem and poke it and the cable in from the outside, pull it up, use a bit of sealant, and then screw down the nut.