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Originally posted by Leon Sisson

Re: "But shouldn’t I bed the bezel with something also?"
 
I suggest trying butyl tape.  It seals tenaciously, doesn't become brittle over time, squeeze-out is easy to clean up, and it's easy to get back apart when the time comes.  And yes, be sure to seal the exposed plywood core, just in case whatever sealant you use eventually leaks.
 
Re: "I’m planning to leave the old gauge..."
 
If you don't mind me asking, what size and shape hole would removing your old Standard Horizon depth sounder leave?
 

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Originally posted by Steve Milby

Have you considered covering the old hole with 1/4" thick white Star Board, or perhaps with a disc cut out of a 1/4" thick white plastic cutting board, which I think is the equivalent of Star Board? You could then cut an opening in the Star Board for the new instrument to fit in. The white cover would match the existing gel coat, and would look like a trim ring.

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Originally posted by Voyager

Hey there Lucky Duck,
I'm the person who repurposed the old Standard Horizon enclosure and mounted the Hawkeye depth gauge inside. It was easy-peasy. I popped the steel ring that holds the backing plate off and unscrewed the switch on the face of the gauge off the glass. The whole internal mechanism just slid out with the backing plate once free of the glass face.
The remaining aluminum shell is a perfect size to house the new gauge body, and the electrical screw terminals on the rear backing plate allowed a perfect power connector. I drilled a hole to pass the transducer cable through and fitted a rubber grommet to hold the cable in place. Rather than remove it and fill the hole, I’d do my darnedest to reuse the old housing.

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Originally posted by Voyager

That’s a good question, different models from different years could have been designed uniquely. If there’s not a single piece of 4” round glass on the face, but instead some plastic or aluminum with a small window for the display, then you’re right.
I did not remove the original depth transducer from the through-hull fitting behind the keel in the bilge, but I do not use the old one. I disconnected the cable and tied it off down below.
Instead I used the new Hawkeye transducer that came with the gauge and mounted it inside the hull near the old one. I followed the old wire harnesses with the cable.
It shoots through the hull to get a depth reading. I used the toilet bowl wax gasket method to Mount and seal the new transducer to the inside of the hull.

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Originally posted by Voyager

If you search for “wax ring” or “transducer” you’ll find a great number of discussions on the topic.
Bottom line, don’t knead the wax or you’ll introduce air bubbles which will cause intermittency in the display.
The wax gets pretty soft during the heat of summer. That’s why it’s best to place the transducer in a location that will not be disturbed by access to storage of equipment or by shifting items during heavy seas.
I use my Vee berth storage for jackets, sleeping bags and soft goods as well as lines and tackle, so I wouldn’t use that area for the transducer. There’s a hatch under my companionway ladder that I don’t use for storage, so it’s ideal in my case.

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Originally posted by bigelowp

I was in a similar situation but had two instruments: depth and speed. I wanted to install depth and sail/wind instruments (Raymarine 40 (now 50) series) I opted to remove old, have starboard fabricated to cover both but locate new over the old holes. I am lousy at posting pics, but it looks good and now I have depth via internal mounted transducer and wind speed. E-mail for pics and more description.

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Originally posted by Leon Sisson

Transducer Shoot-Thru-Hull Mounting Options
 
Let me start by saying I have nothing against the wax ring method of mounting a shoot-thru-hull transducer, other than the risk of it getting knocked loose.
 
When I phoned a manufacturer's tech support about an adhesive stronger than wax, he recommended epoxy.  I asked how to remove the transducer if it didn't work well in the selected mounting spot (air voids, too thick, etc.)  He said whack it sideways with a big hammer, and buy another transducer.  Hmm.  Not the approach I was looking for.
 
I installed the same model depth finder (Lowrance Hook7) on both my Catalina boats.  I mounted each transducer in a liquid filled reservoir inside the hull.
 
In the Catalina 25, I use the default transducer intended for external transom mount (about the size of a small candybar, pivoting attachment point sticking up from one end, thin sheet SS hinge to screw to transom).
 
For a container to mount the transom transducer under the V-berth, I started with a large PVC sewer pipe cleanout, like a coupling, with female threads on one end, female slip fit at other end.  I trimmed the unthreaded end to match the shape of the hull under the V-berth.  To create a flat surface inside the PVC for the mounting bracket I used thickened epoxy mush with tapped screw holes.
 
I bedded the shaped end of the cleanout to the hull up against the aft locker wall under the V-berth using more thickened epoxy.  In a threaded PVC cover plate I drilled a hole large enough to pass the transducer cable connector.  I top up the water once or twice a year.  (Distilled, if you're a purist about such things.)
 
When ordering the depth finder for the Catalina 22, I had the vendor substitute the manufacturer's shoot-thru-hull transducer kit in place of the transom mount one.  This is a better thought out, more compact, commercial version of what I made for the other boat.  Having a smaller volume, it needs refilling more often.
 
Both installations have been working well for years.
 

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