Depth gauge Transducer?
I'm not exactly sure I know what you're asking, but I'll give it a try. I installed an older flasher type depth sounder in a fixed keel C25 years ago. I installed the transducer under the V-berth, just aft of the thru hull fitting. I laid out a thick bubble free blob of clear silicone adhesive (RTV) and pushed the transducer down into it until it contacted the hull. No holes were drilled, but the effective range was limited to a little over 60 ft. This was OK with me since I only used it to tell me when the keel was getting too close to the bottom, and when the water was shallow enough to drop the anchor.
