Re: What are these things?
It does not have to touch the water. It only needs a seamless interface with it. This is provided by the "cup" being filled with water or mineral oil sufficient to fill the space between the inside of the hull and the face of the transducer. This is the way it was done in my 79 Seafarer. In my 72 I mounted the transducer in a wet spot in the bilge. Occasionally I have to throw a cup of water in the bilge to keep it working.
Seafarer 29 KCB