For my '79 Oday 23, I mounted the transducer for my Lowrance Elite Gold S behind the keel stub, just to the port side. I accessed this spot by reaching behind the "ice box". I had to lie down on the port berth, reaching back through the open area in the cabin underneath the stove pull out in order to find the floor of the bilge.
I picked this area for a few reasons: first, because of the design of the 23, the only flat areas of the hull to mount the transducer (the manufacturer says the transducer must be on a relatively flat surface, not an angled surface) are amidships and in the after quarters. You can't mount a transducer in the easily-accessed flat bilge in the main cabin. That entire area is over the stub keel, where the transducer won't work. The bow sections with good access to the bilge (under the v-berth) looked too sharply angled for mounting. If your transducer is more forgiving of angled surfaces and you do want to mount it under the v-berths, getting the cable back to the main unit will be a nice piece of work. In the Oday 23, that will require drilling some holes through the stringers supporting the cabin, and stringing the cable through some relatively inaccessable areas. I know it can be done, as the previous owner of my boat had mounted a through hull knotmeter under the vberth and strung the cable back to the meter mounted on the port cockpit bulkhead. I suspect they used an electrician's snake to make it happen. I wound up using a lot of the knotmeter installation to assist me in installing my new Lowrance. I cut the knotmeter cable (it never worked anyway) and used it to pull the new transducer cable up between the interior and exterior bulkhead walls. I also removed the knotmeter display and used the hole it formerly inhabited to mount the new Lowrance, threading the new cable where the old cable used to sit. I abandonded the rest of the knotmeter cable in place.
So the only area that is flat and accessible on the Oday 23 is the area behind the keel. I had to stretch my arm out to be able to clean and sand the mounting area, but I could do it. I applied epoxy to the transducer as instructed, then held it in place by leaning a heavy monkey wrench on top of it until the epoxy cured. Works like a charm!
